From Cave Art To Hubble: A History Of Astronomical Record Keeping 3030316874, 9783030316877, 9783030316884

Since ancient times, humans have been engaged in a continual quest to find meaning in and make sense of sights and event

209 66 4MB

English Pages 269 Year 2019

Report DMCA / Copyright

DOWNLOAD FILE

Polecaj historie

From Cave Art To Hubble: A History Of Astronomical Record Keeping
 3030316874,  9783030316877,  9783030316884

Table of contents :
Contents......Page 6
Recording the Night Sky......Page 9
A Landmark Day......Page 12
Forwards to the Past......Page 15
Primitive Artwork......Page 16
The Pictograph......Page 17
Knowledge of the Skies......Page 20
Gobekli Tepe......Page 21
Lascaux......Page 22
Ach Valley Tusk Fragment......Page 24
Nebra Sky Disc......Page 28
The Dendera Zodiac......Page 31
The Farnese Atlas......Page 34
The Revolution in Depicting the Night Sky......Page 36
History of the Astrolabe......Page 37
Construction of the Astrolabe......Page 44
Documenting Explosions in the Heavens......Page 46
The Supernova of 1054......Page 48
Chinese and Japanese Records......Page 51
The Arab World......Page 54
Native American......Page 55
European and American......Page 60
RCW 86......Page 65
SN 1006......Page 67
SN 1181......Page 72
SN 1572......Page 74
SN 1604......Page 78
SN 1885A......Page 83
SN 2003 fg......Page 85
The Planet Mercury......Page 87
Early Observations of Mercury......Page 92
Transits of Mercury......Page 97
7.: Mapping the Sky, From Shi Shen to Charles Messier......Page 99
The Greeks......Page 100
The Egyptians......Page 102
Ancient Chinese......Page 107
The Persians......Page 113
Europe......Page 117
Digital Age......Page 126
Earth’s Sister World......Page 127
Revising Kepler’s Rudolphine Tables......Page 131
Observation of the Transit......Page 134
Early Records......Page 140
Chinese Astronomers......Page 141
Greek Astronomers......Page 146
The Middle Ages......Page 148
Early Modern Period......Page 149
Late Modern Period......Page 154
Comet of 1910......Page 157
The Ultimate Recording Methodology?......Page 159
A Dedicated Place to Observe the Skies......Page 168
Stonehenge......Page 169
Wurdi Youang......Page 171
Goseck Circle......Page 172
Kokino......Page 173
Cheomseongdae......Page 174
Gaocheng Astronomical Observatory......Page 178
Uraniborg Observatory......Page 179
Paris Observatory......Page 181
Royal Greenwich Observatory......Page 184
Radio Astronomy......Page 186
Observatories Above Earth......Page 189
The Future of Space Travel......Page 211
Gamma Ray, X-ray, and Infrared – Multi-Messenger Astronomy......Page 212
Fossils......Page 220
Tree Rings......Page 223
Solar Storms......Page 225
Comet Impact or Supervolcano?......Page 229
Ice......Page 231
Antarctic Impacts......Page 234
Supernovae......Page 236
Glossary......Page 237
Index......Page 263

Citation preview

Jonathan Powell

From Cave Art to Hubble: A History of Astronomical Record Keeping

Astronomers’ Universe

Series editor Martin Beech, Campion College, The University of Regina, Regina, Saskatchewan, Canada

More information about this series at http://www.springer.com/series/6960

Jonathan Powell

From Cave Art to Hubble A History of Astronomical Record Keeping

Jonathan Powell Ebbw Vale, UK

ISSN 1614-659X     ISSN 2197-6651 (electronic) Astronomers' Universe ISBN 978-3-030-31687-7    ISBN 978-3-030-31688-4 (eBook) https://doi.org/10.1007/978-3-030-31688-4 © Springer Nature Switzerland AG 2019 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recording the Night Sky . . . . . . . . . . . . . . . . . . . . . . . . . . A Landmark Day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forwards to the Past . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

   1    1    4    7

2. Cave Paintings That Recorded the Night Sky . . . . . . . . . . Primitive Artwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Pictograph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Knowledge of the Skies . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gobekli Tepe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lascaux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

   9    9   10   13   14   15

3. Other Ways the Ancients Kept Astronomical Records . . .   17 Ach Valley Tusk Fragment . . . . . . . . . . . . . . . . . . . . . . . . .   17 Nebra Sky Disc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   21 The Dendera Zodiac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   24 The Farnese Atlas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   27 4. The Astrolabe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Revolution in Depicting the Night Sky . . . . . . . . . . . History of the Astrolabe . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction of the Astrolabe . . . . . . . . . . . . . . . . . . . . . .

  29   29   30   37

5. Supernovae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Documenting Explosions in the Heavens . . . . . . . . . . . . . The Supernova of 1054 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chinese and Japanese Records . . . . . . . . . . . . . . . . . . . . . . The Arab World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Native American . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . European and American . . . . . . . . . . . . . . . . . . . . . . . . . . .

  39   39   41   44   47   48   53

vi

Contents

Other Records of Supernova . . . . . . . . . . . . . . . . . . . . . . . . RCW 86 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SN 393 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SN 1006 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SN 1181 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SN 1572 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SN 1604 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SN 1885A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SN 2003 fg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

  58   58   60   60   65   67   71   76   78

6. Mercury Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Planet Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Early Observations of Mercury . . . . . . . . . . . . . . . . . . . . . . Transits of Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

  81   81   86   91

7. Mapping the Sky, From Shi Shen to Charles Messier . . . . The Greeks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Egyptians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ancient Chinese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Persians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Digital Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

  93   94   96  101  107  111  120

8. The 1639 Transit of Venus . . . . . . . . . . . . . . . . . . . . . . . . . Earth’s Sister World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Revising Kepler’s Rudolphine Tables . . . . . . . . . . . . . . . . . Observation of the Transit . . . . . . . . . . . . . . . . . . . . . . . . .

 121  121  125  128

9. Comets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A Fiery Visitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Early Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Chaldeans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chinese Astronomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Greek Astronomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Middle Ages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Early Modern Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Late Modern Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comet of 1910 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ultimate Recording Methodology? . . . . . . . . . . . . . .

 135  135  135  136  136  141  143  144  149  152  154

10. Astronomical Observatories . . . . . . . . . . . . . . . . . . . . . . . . A Dedicated Place to Observe the Skies . . . . . . . . . . . . . . Ground-Based Observatories . . . . . . . . . . . . . . . . . . . . . . . Stonehenge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wurdi Youang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

 163  163  164  164  166

Contents

vii

Goseck Circle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kokino . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cheomseongdae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gaocheng Astronomical Observatory . . . . . . . . . . . . . . Uraniborg Observatory . . . . . . . . . . . . . . . . . . . . . . . . . . Paris Observatory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Royal Greenwich Observatory . . . . . . . . . . . . . . . . . . . . Radio Astronomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Observatories Above Earth . . . . . . . . . . . . . . . . . . . . . . . . . The Future of Space Travel . . . . . . . . . . . . . . . . . . . . . . . . . Gamma Ray, X-ray, and Infrared – Multi-­Messenger Astronomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

 167  168  169  173  174  176  179  181  184  206

11. Fossils, Tree Rings, and Ice . . . . . . . . . . . . . . . . . . . . . . . . . Mother Nature’s Records . . . . . . . . . . . . . . . . . . . . . . . . . . Fossils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tree Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar Storms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comet Impact or Supervolcano? . . . . . . . . . . . . . . . . . . . Ice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Antarctic Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Supernovae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

 215  215  215  218  220  224  226  229  231

 207

Glossary ���������������������������������������������������������������������������������������233 Index���������������������������������������������������������������������������������������������259

1.  Introduction Recording the Night Sky Throughout history, the desire to document happenings and events has been an integral cornerstone in humankind’s advancement to acknowledge, understand, and preserve the very fiber of what the eye beholds, which in turn contributes to our ultimate survival and existence. This fiber remains intertwined between our past and present, with the present allowing our future selves to grow and nurture, learning from what past knowledge has been acquired. Without this kernel of guidance through documentation of the past, there would be no root from which to develop, no steering wheel, no beam of light to shine forward into the enveloping darkness of an uncertain future. History is a vital link in an extensive chain that binds humankind, its thoughts, its reactions, and its judgements. This is in some cases a necessary evil but also, by the same token, both a positive attribute and ultimate tribute, the veritable recording of life’s tapestry, which in turn unfolds over time, revealing a picture whose sum total is greater than the individual mosaic-like artwork that forms it. From the seemingly simple artwork that adorns many cave walls throughout the world to the high-end spectrum of modern recording capabilities, the documenting of the night sky has created a catalog of our history on Earth, a history that generations of custodians have seen fit to record as an often-permanent record of their time on Earth. As much as fossils give vital clues to understanding the creatures that once roamed the land, artwork can yield very much the same results if looked upon and studied sufficiently. Interpretation is the key that unlocks the past. Let us not forget the number of times a species of which nobody knew the existence of is discovered, adding to the everincreasing back catalog of animal life that lived on land, dominated the skies and swam in our oceans. Every time there is a new discovery, another part of the jigsaw is acquired – a jigsaw that will

© Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_1

1

2

1. Introduction

probably never be completed, as new finds add an extra dimension to our understanding, changing our perceptions, as much as they deepen and enhance our knowledge of the past. It might once have been said of early cave art and engravings, that these were – simple cave drawings by a primitive and intellectually deficient collection of our human ancestors. Perhaps at first this may well have been the way in which such findings were viewed, but as the decades have passed, new light has been thrown on the cave drawings, a light that has shone beyond the ignorance and often arrogance of a society that at the time was possibly too quick to dismiss, too hasty in judging, and ultimately wrong in determining the meaning behind such work, and those who created it. A precedent exists for not being as dismissive as those who went before us, as such simple drawings can in fact reveal much more than initial viewing may suggest. It is hard to believe that as the decades pass, ground-breaking advances in many areas of science will not continue and, in retrospect, the discoveries of today merely serve as the notches of forward progression towards a better way of understanding, a fresher way of comprehending, and a simpler and more satisfying way of conquering that which serves to halt progress most  – in many cases, humankind itself. Many years from now, what we believe to be cutting-edge will be so dated and antiquated that our future selves to may look back with bafflement as to why what seems so obvious at that point didn’t seem so in the past. Fundamentally, this applies to cave art and the causal link between the intellectual level and reason the drawings were made by the people who made them, and the actuality and reality that have been bestowed amongst our ancient relations. Although modern technology used to record the sky is ultimately more comprehensive, more intense, with possibly for some an elitist edge that precludes everyone’s involvement, and cave art perhaps a more collective endeavor, the parallels between the two forms are unequivocally linked. From Cave Art to Hubble attempts to address all the various methods used to record the night sky throughout history. Although the book strives to cover the array of potential documenting applications, be it in the form of art, the work of a scribe, or one who weaves patterns on fabric to the number cruncher at

Recording the Night Sky

3

the receiving end of a data transmission, the aim is ultimately to establish one determining link. First, we will look at a lone observer from ancient times simply peering up into the night sky with just their eyes. Then we will look to the present day, with a lone observer doing exactly the same. What they see before them in relative terms isn’t all that different, for in front of them is a black velvet canvas with a vast array of stars, the same then as it is today, with perhaps the Moon for company. But although it is seemingly the same sky, the concept of what is being observed has altered vastly  – virtually the same stars, but with a very different reckoning now as to what they are, how they were formed, and in relation to other stars, our very own place in the cosmos. As we have learned and grown in scientific stature, our ability to record and interpret has evolved with it. We can see from our ancestors how the recording of the sky was as important to them as it is to us today, and why it is necessary to continue that growth in how we perceive the sky. The very essence of our existence and the ability to understand and advance is underpinned by our own comprehension of the universe, and while a good many theories, explanations, and ultimately confirmed facts are established, the sum total makes for just a fraction of the overall picture that perhaps someday will be concluded. Who would have dared to challenge some of the early beliefs surrounding the makeup of our own Solar System? And yet, through progress and proof, acceptance has also often then entered the equation – acceptance that one notion was wrong and another right, an explanation with cast-iron proof. We are still very much finding our way in the cosmos, still on a very long path, and still looking for clues and guidance towards unlocking so many mysteries, the answers many of which lie in the stars. Early humankind recognized the importance of preserving their own sightings in the night sky, and over the centuries, though the ways of recording events in the heavens has changed, the basic instinct that exists to relate and interpret what has been seen remains the same. Even though from the depths of our oceans to the deepest rainforests many places right here on Earth remain uncharted, surely the greatest adventure of all lies above us. And what better way to set sail than when accompanied by the recollections and findings of others throughout the centuries, offering one of the biggest, ongoing learning curves that humankind could embrace, and

4

1. Introduction

by advancing the way in which we document the skies, the sum total of all our findings could potentially offer answers to questions that have been asked. Does the answer lie within? Does all the cave art, stone tablets, parchments, letters, woven fabrics, telegraphed communications, radio waves and microchip data, provide the answers to so many questions that already exist, and it’s just that we can’t see it, or do we not know enough to determine it or equate in a context that makes it comprehendible? The quest for knowledge continues by reaching farther and farther into the depths of space, studying astronomy and cosmology; the further we look, the farther back we go in space and time. We edge forwards towards the very past that brought us here to the present. However, we must not be complacent. There are so many potential ‘game-changers’ as we push forward, and the history that we have recorded down the centuries is ultimately cross-referenced with the history of the cosmos that is being uncovered as we peer deeper and deeper into our past, by looking into more remote parts of space.

A Landmark Day When examining all the methods used to record the night sky, several universal truths exist. Firstly, every format has its merit and subsequent time marker stamped by what method was used, by whom, and for what purpose. Secondly, not all of the events recorded in the night sky were of the “now” and, particularly when considering views of the stars and constellations, were recordings of past events. Given the great distance that light travels before being finally captured, a lot of what we see on a nightly basis happened long ago, when our ancestors were custodians of Earth during their “tenancy.” Thirdly, and most importantly, the further we look into space, the farther back we see in time, which ultimately creates a staggering paradox. We look further to gain more knowledge and understanding of the universe, but in essence, like an archaeologist, the further we plough the depths of space, the deeper we reach into our own past.

A Landmark Day

5

Fig. 1.1.  Black hole in M87. Event Horizon Telescope. (Courtesy of NASA)

One such event in 2019 summed up what From Cave Art to Hubble is all about, the very core of its structured aim. For in April, the eyes of the world turned to Messier 87 as astronomers released the first ever image of a black hole. This was a monumental moment in science, as after centuries of theories and debate, we at last had an actual image to which black holes could be tagged (Fig. 1.1). A year previous to this ground-breaking image, news broke of research that suggested that as many as a dozen black holes may lie at the center of our own galaxy, supporting a widely held theory that “supermassive” black holes at the centers of galaxies are surrounded by many smaller ones. A Columbia University-led team of astrophysicists made the discovery of the black holes in 2018, which are gathered around Sagittarius A∗ (Sgr A∗), a supermassive black hole right at the center of the Milky Way. Sagittarius A possesses four million times the mass of our own Sun and is located 26,000 light years from Earth. A year later and scientists had their first image of what turned out to be a gargantuan black hole, with a mass equivalent to 6.5  billion times that of our Sun. The galaxy surrounding it, Messier 87 in the constellation of Virgo, is equally huge. Known as a supergiant elliptical galaxy, it is one of the most massive galax-

6

1. Introduction

ies in the universe and hosts a large number of globular clusters. An international scientific team heralded the image as “seeing the unseeable,” a spectacle 55  million light years from Earth. The diameter of the black hole is approximately 39 billion km. A black hole is an incredibly dense region of space from which nothing can escape, with this image showing us what in essence is a one-way door leading us out of our universe  – a place that due to its massive gravitational field sees clocks run slower the nearer one advances toward it, although the actual slowing affect is regulated and dependent on the curvature of spacetime around the black hole. The idea of a black hole was first conceived in 1783 by amateur astronomer John Michell (1724–1793). Michell, an English natural philosopher and clergyman, published a paper for the Philosophical Transactions of the Royal Society of London, which was read aloud on November 27, 1783. The paper proposed the idea that there were such things as black holes, which Michell referred to as “dark stars.” Michell, whose other interests included a wide range of topics in the scientific field, including geology, optics and gravitation, proposed that light consists of miniscule particles. He reasoned that such particles, when emanated by a star, would be slowed by its gravitational pull, and in turn surmised that it might be possible to determine a star’s mass based on the reduction of that speed. As a result, it may well be possible that a star’s gravitational pull might be so strong that the escape velocity would exceed the speed of light. At the time of Michell’s paper and despite a similar idea being proposed by French mathematician Pierre-Simon Laplace (1749– 1827) in his 1796 book Exposition du Systeme de Monde, many of Michell’s contemporaries did not buy into his theories on black holes. In actuality, both Michell and Laplace were simply far ahead of their time – but how wrong their contemporaries were and how foolish to dismiss such notions out of hand! Albert Einstein’s (1879–1955) theory of general relativity was formulated in 1915. Black holes were an unprecedented test of whether Einstein’s ideas about the very nature of space and time hold up in extreme circumstances, and they did, as his general relativity – possibly one of the most comprehensive theories ever formulated – had its ultimate confirmation. Along with other great scientists who made invaluable contributions to the theoretical work surrounding black holes, one cannot fail to mention the tireless work of Stephen Hawking

Forwards to the Past

7

(1942–2018), who, born exactly 300 years after the death of Galileo Galilei (1564–1642), devoted his entire life to exploring various theories on cosmic phenomena, including in 1974 his theory that a black hole does in fact emit something when you throw quantum mechanics into the equation. He hypothesized that black holes had an “apparent” horizon, across which matter and light could move, while leaving behind particles, now also known as Hawking radiation.

Forwards to the Past Technology continues to develop with gathering pace, and no matter how we record the night sky in the future, there will always be more than just a tenuous link to the past. For the documenting of such events, while important, only validates one half of whatever image is captured. For here, as we peer into the past, the unraveling of the universe in which we live also marks the passage and development of humankind’s collective ability if a general consensus and understanding is mutually recognized, to pursue greater, more all-encompassing breakthroughs, and like our ancestors who saw and painted on a cave wall in centuries past, impart the knowledge and wisdom of discovery so that future generations can learn, build, and grow in unison. The biggest obstacle is often the one we place in the path of ourselves. Whereas it is hard to estimate exactly where technology will take us next, the excitement lies within the possibilities that the likes of Michell were so keen to suggest, and the marriage of making those theories and then providing evidence of their actuality. The black hole image struck such a chord with many who in their own scientific disciplines believed, and yet who had not at the time of postulating reached the point where proof is provided; but as with time, the truth shall set them free. While that image of the black hole is a huge reckoning moment for humankind, it is but one more milestone ahead of many more milestones to come, as we barely make the smallest of impressions on the world around us. But small or not, it is our impression, and a definitive sign that our fate to a certain extent lies with our drive, passion, and ultimate quest to push back the boundaries of space and time, and for ourselves, to see the past from perhaps whence we all came and will all one-day return.

2. Cave Paintings That Recorded the Night Sky Primitive Artwork One of the most striking and imaginative insights into the life and times of ancient civilizations comes in the form of artwork, sketches, and paintings left on the walls of caves and other dwellings. For here, sometimes in a very uncomplicated format, or in other cases quite elaborate, many events were recorded in graphic form. Whereas the written word would in many cases not be challenged in terms of meaning or the offer of multiple interpretations, some cave paintings have caused much debate as to what the artists were trying to convey through their medium. Aside from the possibility that cave art was just a means of decoration, the very fact that the artist took the time to create them did, without them probably knowing, create a pictorial representation of the times in which they lived. So, whether the artwork was for leisure or purpose, the same outcome was achieved, in so much as a very vivid piece of history was given to future generations, a valuable portal to the past. Indeed, barring fossils, it is the only portal of its kind. But, is there a meaning behind the artwork? Some scientific quarters claim a “key” or a “code” may exist within the artwork and that the paintings may have been a way of transmitting information. Other, perhaps more realistic, explanations lean towards a religious or ceremonial purpose. When considering the possibilities, it does seem hard to believe that any artwork was merely for decorative purposes. Perhaps there was more of a need to convey and confirm to others at that time that the world in which they lived was perceived in the same way, a common ground if you will, where merely pointing to the picture of an animal would create unity in the mutual understanding of what had been drawn and what it represented. Indeed, the art may well depict life experiences or in some way portray a storybook, which would easily act as a means of representing a sequence of events through drawings. © Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_2

9

10

2.  Cave Paintings That Recorded the Night Sky

Prehistoric men may have painted animals to “catch” their soul or spirit in order to hunt them with more ease, or perhaps the vision painting of the animal on the wall was merely some way of paying homage to the surrounding nature and environment in which they lived. The act of drawing would, in turn, fulfill the basic need of expression that is innate to all human beings. Another theory proposes that animal images were in fact actual records of hunts that served the dual purpose of making an inventory of kills, as well as noting down for future reference animal migrating patterns. French archaeologist and paleontologist Henri Breuil (1877–1961) was famous for his studies of prehistoric cave art, particularly those discovered at Altamira, in what is now Spain, and Lascaux, in what is now France, interpreting rock paintings as being hunting magic, meant to increase the number of animals killed by hunting parties. Yet another theory suggests that cave art was a method that early humans used to help cope with the constant struggle for survival – surely one of the earliest forms of self-help! Whatever their purpose and whether or not their creation was meant to determine something greater and more powerful than the images themselves, one cannot ignore the sheer depth of creativity that was demonstrated by the artist, and perhaps the pleasure and pain they felt at the time of their concept.

The Pictograph Cave paintings are a form of rock art. Rock art itself is a term in archaeology for any manmade markings on natural stone, most often referring to markings and paintings on rocks made by Paleolithic and Mesolithic human beings. Rock art itself can be found across the globe, the product of many different cultures. Cave paintings fall under the category pictograph or pictogram, a symbol representing a concept, object, activity, place, or event by illustration. Pictography allows this expression to develop further, with a form of writing in which ideas are relayed through drawing. The drawings and their ultimate survival over the ravages of time, not forgetting the ‘canvas’ of stone on which they were made, is attributable to the use of mineral pigments, most commonly manganese, hematite, malachite, gypsum, limonite, clays, and various oxides. The red colors within a painting were made with iron oxides (hematite), whereas manganese dioxide and charcoal were used for the black.

The Pictograph

11

What is believed to be the world’s oldest drawing is contained on a 38.6-mm-long flake of silcrete (a fine-grained cement of sand and gravel), comprising a few reddish lines drawn on one smooth, curved face using an iron-rich pigment called ochre. Working at the Blombos Cave in the Blomboschfontein Nature Reserve, about 300 km east of Cape Town, South Africa, an archaeologist noticed the markings while analyzing stone flakes and debris excavated from a 73,000-year-old layer of the site. According to Professor Christopher Henshilwood, an archaeologist at the University of Bergen, the lines on the flake might have been bolder and brighter when the drawing was new, but over time they’ve probably lost some pigment through weathering and wear. The design, which features six parallel lines, with three curved lines cutting across them at an oblique angle, would seem to indicate a complex piece of work, and probably a fragment of something originally drawn on a larger surface and later broken. This fascinating find involving cross-hatching is believed to be the earliest known drawing made by a human. The most basic pictography would have seen the artist using wet clay or charcoal, applied to the wall by finger. The production of crayons or paints would have required minerals to have been finely ground and combined with binding materials. Apart from fingers, twigs were used as well as moss, horsehair brushes, and also bone or reed tubes through which the paint was literally blown against the wall. The oldest known ‘painting kits’ used in the Stone Age were also unearthed at the Blombos cave in South Africa. Two sets of implements for preparing red and yellow ochres to decorate animal skins, body parts, and cave walls were excavated. The stone and bone tools were used for crushing, mixing, and applying the pigments, with the shells of giant sea snails utilized as primitive mixing pots. The sea snails were indigenous to the area, as the Blombos cave is situated on the southern cape of South Africa, near the Indian Ocean. Other bones, including the shoulder blade of a seal, were among the ingredients for making the pigments. It is thought that the bones were probably heated in a fire, and the marrow fat then used as a binder for the paint. Water or urine was added to make the paint more fluid. According to Henshilwood, the cave artists used small quartzite cobbles to hammer and grind the ochres into a powder, which was then put into the shell and mixed with charcoal, burnt and broken bone, with a liquid or liquids then added. One of the most revealing finds came in the form of a front leg bone of a dog or a

12

2.  Cave Paintings That Recorded the Night Sky

wolf with one end dipped in ochre, leading the team to believe that it was in fact used as a primitive paintbrush! One of the most common rock art elements found around the globe was that of the human hand. One such type of pictograph using the human hand was a technique that had been around since Neolithic times – simply spraying around the hand, resulting in a negative image. The more common positive print was often made with pigment applied to the hand and transferred to the rock. The subject of the artwork varied greatly, but included the Aurora Borealis. Some of the drawings made by the Cro-Magnon people on the walls and ceilings of caves in southern France most probably depict the northern lights. These drawings date back 30,000 years (Figs. 2.1 and 2.2).

Fig. 2.1.  Macaronis aurora drawings (Courtesy of NASA.)

Fig. 2.2. Aurora drawings from 1570 (Courtesy of the Royal Edinburgh Observatory)

Knowledge of the Skies

13

Knowledge of the Skies In November 2018, researchers at the University of Edinburgh published findings that suggested prehistoric cave dwellers had quite a sophisticated knowledge of the skies, in particular the constellations. This would seem to suggest that there was much more to the artwork than just drawings of humans, animals, and the hunting that took place to find food to fuel everyday life. The researchers, including Dr. Martin Sweatman, who helped lead the team and who co-authored the resulting scientific paper, studied a number of caves containing such artwork in Turkey, France, Spain, and Germany. The artwork showed a consistent set of symbols, keys if you will, revealing how ancient civilizations actually tracked astronomical events. With a distinct parallel between the animal-based shapes of our constellations and astrological signs, there is also a correlation between the animals and the placement of stars at a specific time. The researchers looked at examples of Paleolithic and Neolithic art throughout the four countries in order to decode the specific symbols that had been chosen to represent constellations and individual stars. Dr. Sweatman, a professor at the University of Edinburgh, along with a team of researchers that incorporated teams from the University of Edinburgh and the University of Kent, then set about chemically identifying the paints that had been used, employing Stellarium software to compute the position of constellations at the relevant solstices and equinoxes. The results from the radioactive carbon dates and the Stellarium calculations revealed some consistent findings. The cave art reveals that, in essence, humans from as long as 40,000  years ago appeared to have accurately kept track of time by watching how stars slowly change their positions in the night sky. This phenomenon, known as precession of the equinoxes, is caused by a gradual shift of Earth’s rotational axis. The discovery of this motion was previously credited to the ancient Greeks thousands of years later, but upon deciphering the cave art, we know this dates back considerably further. Indeed, generally credited to Hipparchus of ancient Greece in the second century b. c., the researchers’ findings show that the same ­constellations, and indeed precession, were known some 35,000 years earlier. At every site visited, the cave artists practiced a method of timekeeping based on astronomy, despite the fact that the paintings were found in four different countries and separated in time by tens of thousands of years.

14

2.  Cave Paintings That Recorded the Night Sky

The findings confirm a greater level of understanding among our primitive ancestors than was previously thought. What was being depicted with a concurrent theme throughout the examined cave art was a method of record keeping that, by its limited complexity, revealed that ancient humankind actually had much better understanding of the night sky than they were originally given credit for. Furthermore, the understanding of the skies would also suggest a greater than expected knowledge of the seas, with stars and constellations used as navigation tools, which, in turn, would have aided prehistoric human migration. Such findings about the level of understanding would also give credence to the notion that, as a parallel, early cave art actually shows such a level of advancement with regard to understanding of the night sky within the last ice age; on an intellectual comparison, there is very little difference between those who existed then and modern-day humankind.

Gobekli Tepe Working alongside colleague and co-author of the scientific paper Alistair Coombs, Sweatman decoded artwork at Gobekli Tepe, an ancient Turkish archaeology site, 6  miles from Urfa, an ancient city to the southeast. The site was first extensively examined by University of Chicago and Istanbul University anthropologists in the 1960s. As part of a survey that swept through the region, they visited Gobekli Tepe (which means “belly hill” in Turkish), sighting some broken slabs of limestone and assuming that the mound was nothing more than an abandoned medieval cemetery. Later, Klaus Schmidt, a German archaeologist, revisited the site, taking more of an interest in what was found at the location. Schmidt discovered massive carved stones about 11,000  years old, crafted and arranged by prehistoric people who had not yet developed metal tools or even pottery. The megaliths, which predate Stonehenge by some 6000 years, led Schmidt, who had been working at Gobekli Tepe for more than a decade, to claim that this was the site of the world’s oldest temple. With Gobekli Tepe considered to have dated from roughly around 11,000 b. c., based on the insights into the astronomy observed at the site.

Lascaux

15

Sweatman and Coombs claim that an ancient stone pillar at Gobekli Tepe, referenced as Pillar 43 of Enclosure D, depicts on its west-facing side the commemoration of a devastating meteor impact in North America that led to the Younger Dryas Event, a period of sudden climate cooling that triggered a mini ice age across the northern hemisphere. The date carved into the stone, widely known as the Vulture Stone, can be deciphered as 10,950 b. c., within 250  years of the impact. The date was written using the precession of the equinoxes, with animal symbols representing star constellations corresponding to the four solstices and equinoxes of that year. Ice core samples taken from Greenland add weight to the evidence that suggest a comet may have led to the onset of the Younger Dryas Event, which lasted approximately 1000 years and had a distinct global cooling effect.

Lascaux Situated near the village of Montignac, in the Dordogne region of France, is a complex of caves known as Lascaux (French, Grotte de Lascaux), where over 600 parietal wall paintings cover the interior walls and ceilings. Alongside the 600 paintings are 1500 engravings. The paintings represent primarily large animals with flora and fauna corresponding to fossil records dating from the Upper Paleolithic time. This time period is the third and last subdivision of Paleolithic, or the Stone Age, broadly incorporating the period between 50,000 and 10,000 years ago (the beginning of the Holocene epoch), before the advent of agriculture. Unlike other caves, Lascaux, whose protective layer of chalk had made it watertight, had been completely sealed for so long that even today debate remains about how the prehistoric artists entered the caves to draw upon and engrave its walls. The entrance to Lascaux was discovered on September 12, 1940, by a teenager named Marcel Ravidat (1923–1995), who upon making the discovery returned to the scene with three friends, Jacques Marsal, Georges Agnel, and Simon Coencas. Here, in an attempt to rescue their dog, who had fallen into a hole while chasing a rabbit, the teenagers entered the cave through a 15-m-deep shaft at the end of which was revealed the now famous gallery of ancient artwork. The hole that the dog had fallen down had been

16

2.  Cave Paintings That Recorded the Night Sky

created the previous winter, when a tree in the oak woods was uprooted by a storm, tearing away several feet of Earth. The story of Marcel Ravidat’s black and white dog, named Robot, falling down a hole doesn’t appear to be the only explanation as to how the caves were discovered. Other sources believe Marcel, at the time, an 18-year-old apprentice garage mechanic, along with his friends, were actually out searching for a fabled underground passage that led to a nearby chateau! The galleries have since been given names, including the Hall of Bulls, the Passageway, the Shaft, the Nave, the Apse, and the Chamber of Felines. The artwork and drawings at Lascaux are the combined effort of many generations, and because so many have contributed to the vast number of works, much debate still surrounds the dating and whose input we are actually witnessing. The Shaft scene features a dying man with a horse, bison, bird, rhinoceros, and geometric shapes surrounding him. Though this mural was once interpreted as an abstracted narrative about life and death, the findings of Sweatman and Coombs suggest that the scene does in fact commemorate a comet strike on Earth that occurred around 15,200 b. c. Sweatman and Coombs believe the artwork depicts a major damaging event, in which debris that heralded from the direction of Capricornus, namely remnants of a comet that fuel the Taurid meteor stream, impacted on Earth. The interpretation supports the theory of “coherent catastrophism,” which, according to Sweatman, describes how a large comet became trapped in the inner part of our Solar System many thousands of years ago, creating a stream of debris that intermittently collides with Earth, albeit on an irregular basis.

3. Other Ways the Ancients Kept Astronomical Records Ach Valley Tusk Fragment Besides the speculation and conjecture that many cave drawings have sparked, such artwork is not the only form of potential record that exists from ancient times. One piece of art in particular that has caused similar debate is known as the Ach Valley tusk fragment. Although the cave drawings have shown that astronomical phenomena that we can all relate to, the problem remains as to identifying the motive as to why it was recorded and establishing which event it may be symbolizing. Indeed, there is a danger of overcomplicating by trying to parallel any event in the night sky with such art, but whereas in modern day astronomy liberally photographing parts of the sky may be done simply for sheer interest or to test the capabilities of a camera, the motive from bygone years did not have a casual motive attached; it seems to have been done for more of a definite reason, like an eclipse, or the appearance of a bright comet, something that stirred whoever drew the art to record it. Therefore, it would stand to reason that all recorded artwork of this nature had to have a given connection to an event, a happening, something that may have instilled a combination of fear and curiosity to the point where the event needed to be recorded. However, as a counterbalance to that argument, one may point out that there are numerous drawings and artwork that depict everyday life, including animals, certainly an aspect of life that did not occur on a random basis, like the outburst from a supernova. The Ach Valley tusk fragment moves this argument onto a different level, as its creation and what it is supposed to represent throw light onto a different dimension on how the night sky was viewed, and proved that besides drawings, sketches, and colorful cave art, there are other ways to capture the night sky.

© Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_3

17

18

3.  Other Ways the Ancients Kept Astronomical Records

Discovered inside the Geibenklosterle cave in the Swabian Alps of southwestern Germany, the Ach Valley tusk fragment bears the image of an upright figure thought to represent the constellation of Orion the Hunter. Could it be that this artifact carved into a mammoth ivory fragment during the Ice Age is actually the representation of a constellation, and not just the depiction of a person from that era? Is it perhaps not just an excellent example of skill and workmanship from the Ice Age – how one being was able to capture another in such distinct detail? If it is a carving of Orion, it would make for the oldest known depiction of a star map, with an age in excess of 32,000 years. The carving measures 38 mm × 14 mm × 4 mm and was discovered inside one cave that makes up an entire complex of caves that were inhabited during the Upper Paleolithic epoch, which lasted from about 50,000 to about 10,000 years ago. Excavations at the site revealed six different layers that correspond to six different periods of habitation by separate cultures, including the Aurignacian culture, of which little is known, aside from the established fact that its people were inhabitants of the cave about 32,000 years ago, and that, as a people, they were master carvers of mammoth ivory. Associated with European early modern humans (EEMH), it is believed the Aurignacians originated from the earlier Levantine Ahmarian culture, considered to be the likely source of the first modern humans who migrated to Europe to form the Aurignacian culture, with the people known as Cro-Magnons. This term derived from the Cro-Magnon rock shelter in southwestern France where the first EEMH were found in 1868. The Aurignacians were characterized by worked bone or antler points with grooves cut in the bottom. They used flint tools, including fine blades and bladelets, with a distinctly more refined approach to their workmanship. This, along with a great level of self-awareness, led archaeologists to consider the makers of the Aurignacian artifacts to be the first modern humans in Europe. Beside the Ach Valley tusk fragment, figurines have been found depicting faunal representations of the time period including now-extinct mammals, such as mammoths, along with anthropomorphized depictions that may be interpreted as some of the earliest evidence of religion. In the Vogelherd Cave in Germany, many 35,000-year-old animal figurines have been discovered, with one of the carvings, a horse, found among six tiny mammoth and horse ivory figures,

Ach Valley Tusk Fragment

19

having been sculpted as skillfully as any piece found throughout the Upper Paleolithic. Other finds included bone flutes, harpoons and barbs, pendants, beads, ivory and stone spear points, arrow points, clubs, and scrapers. However, arguably the most impressive finds were the intricately carved statuettes, some of which consisted of women that became to be known as the Venus figurines. These figurines emphasize the hips, breasts, and other body parts associated with fertility. Feet and arms are lacking or are minimalized. Interestingly, there are fewer sculptures depicting men or figures of uncertain sex. One such Venus figurine is known as the Venus of Hohle Fels, carved from mammoth ivory and unearthed in 2008 in Hohle Fels, a cave near Schelklingen in Germany. It has been dated to between 35,000 and 40,000 years-old, belonging to the Aurignacian period. The figure is the oldest undisputed known example of a depiction of a human being. In terms of figurative art, only the lion-headed zoomorphic (animal-shaped) Lowenmensch (lion-human) figurine is older, discovered in Hohlenstein-Stadel, a German cave, in 1939. With such great workmanship evident from the Aurignacian period, there remains little doubt of the age of the Ach Valley tusk fragment and the peoples who sculpted the work. But where is the link to establishing the piece as being associated with the constellation of Orion? The theory was proposed by Dr. Michael A. Rappengluck, a well-respected academic with a background in astronomy and archeoastronomy, who, via a research paper, suggested that astronomer-priests in European Upper Palaeolithic cultures could ‘see’ constellations in the night sky, recording the findings in cave art, calendars, and sculptures such as the Ach Valley tusk fragment. Dr. Rappengluck’s proposal was not a new one, with other academics also suggesting such a correlation. Several factors when analyzing the Ach Valley tusk fragment would lend support to Dr. Rappengluck’s proposal. Firstly, it is not a broken fragment but a complete fragment in itself, not part of a greater work. The carving clearly portrays a man-like figure with outstretched arms, a pose that is a match to the stars of Orion. The notches on the back side of the Orion figure are a primitive pregnancy calendar for predicting when a woman will give birth. In total, there are 86 notches, which is the number of days to be subtracted from the day count of one year to arrive at the average number of days in the human gestation period, 86. The number is also the number of days that Betelgeuse, one of Orion’s two most prominent stars, is visible to the naked eye each year. However,

20

3.  Other Ways the Ancients Kept Astronomical Records

the premise of notches and numbers must be an open item for consideration when debating the likelihood of an association between the carving and Orion, for it dictates that the Aurignacian culture could count and had a basic grasp of arithmetic with a general understanding of its mechanics, and also that they knew how many days there were in a year. One of Dr. Rappengluck’s claims was that the 86 notches on the carving represents the number of days that one of Orion’s principal stars, Betelgeuse, is visible, this forming a link between the sky gods and human fertility. The tusk fragment figure has arms raised and legs spread apart, with what appears to be a sword hanging between his legs. His left leg is shorter than his right leg, exactly as the constellation depicts Orion, with the tiny waist of the tusk fragment mirroring the bright stars in the belt of Orion. In order to simulate the stellar positions of the stars in Orion over the past thirtieth centuries, Dr. Rappengluck used advanced planetarium software to “wind back” the years to where the stars in the constellation would have been at the time the fragment was actually carved. The results showed a perfect match between the planetarium software and the carving. The correlation, striking as it appeared, was still not absolute proof, and perhaps one of the factors for unraveling the whole idea lies within other artifacts found in the Geibenklosterle cave. Among the findings were hundreds of small, carved figurines of mammoths, bears, and other animals. One animal depicted was what appeared to be a bison, displaying such lavishly attended to details as horns and beard, but it’s the size of the carving that demands more scrutiny. Measuring only 25.5 mm × 14.5 mm × 6 mm, the carving is comparable to the dimensions of the human-like figure allegedly representing Orion, which begs the question, why were no similar comparisons made between the bison figure to represent another notable constellation, that of Taurus, or indeed, any other constellation? Furthermore, given the range of objects detailed in the find, surely there should be at least several more parallels drawn between objects discovered and phenomena observed in the night sky by the people who made the carvings? Aside from the lack of other parallels made between findings and the night sky, a question mark can be firmly placed against the identification of Orion’s sword. Astronomers viewing the night sky with no optical aid, even today, must envisage such a sword as there are no clear observational criteria to point out such a thing,

Nebra Sky Disc

21

in so much as Orion’s belt is defined. Indeed, viewing where the sword actually is demands the observer to envisage the sword. If this is the case today, then since no artifact was discovered in the Geibenklosterle cave that actually was a sword, how could the carver have placed a sword there? Whoever made the carving would have had no knowledge of the existence of swords, yet Dr. Rappengluck claims that the so-called Orion carving clearly shows a sword.

Nebra Sky Disc Aside from the Ach Valley tusk fragment, other such artifacts prove less of a puzzle, at least in identifying a specific relationship to the night sky. One such artifact is the Nebra sky disk made of bronze, measuring 32  cm in diameter with a weight of 2.2  kg. The disk has been dated to 1600 bce, with a manufacture date of 200 years before that, and was discovered by treasure hunters in 1999 while metal detecting at a prehistoric enclosure encircling Mittelberg, (“Central Hill”), near the town of Nebra in the Ziegelroda Forest, approximately 180 km southwest of Berlin. Situated 60 km from Leipzig, the surrounding area in Mittelberg is known to have been settled in the Neolithic era. The enclosure is orientated in such a way that the Sun seems to set every solstice behind the Brocken, the highest peak of the Harz Mountains, approximately 80 km to the northwest. At a height of 1141 m, Brocken is the highest peak of northern Germany, with the next most prominent peak if traveling east in a straight line the Ural Mountains in Russia. Thought by many researchers to be the oldest known realistic representation of the cosmos, there has been much debate as to its potential usage, perhaps as a kind of astronomical tool to determine planting and harvest times. The disk has a blue-green patina and is embossed with gold leaf symbols, which appear to represent a crescent Moon, the Sun, (or perhaps a full Moon), stars, a curved gold band, interpreted as a “sun boat,” and a further band on the edge of the disk that probably represents one of the horizons. Twenty-three stars appear to be dotted around randomly, with a further cluster of seven stars taken to be the Pleaides star cluster. Another gold band on the opposite side is missing. This could well have been damaged during its rather crude excavation from the ground by the treasure hunters, with other noticeable marring of such a fine piece includ-

22

3.  Other Ways the Ancients Kept Astronomical Records

ing the splintering of its outer rim, the loss of one of the stars, and general unnecessary mishandling. When attempting to sell the piece, the law intervened, stating that the Nebra Sky Disk belonged to the state of ­Sachsen-­Anhalt, where it was unearthed along with numerous other items, including two swords and two axes. X-rays have revealed two more stars underneath the gold of the right arc, suggesting that the two arcs were added later than the other features. It has also been discovered that the blue-green backdrop of the night sky was once colored differently, that of a deep violet-blue, apparently by applying rotten eggs, causing a chemical reaction on the bronze surface. Running along the edge of the disk is a ring of holes punched through the metal, probably for attaching the disk to perhaps a heavy piece of heavy cloth. Also present with the Sun boat or solar barge are oars shown as multiple strokes, being perhaps a mythological representation of the Sun riding in a boat. The style in which the disk was executed was unlike any artistic style then known from the period, with the result that the Nebra Sky Disk was originally suspected to be some form of forgery, although the piece is now widely accepted as authentic. The find is also regarded as reconfirming that the astronomical knowledge and abilities of the people of the European Bronze Age included close observation of the yearly course of the Sun, and the angle between its rising and setting points at the summer and winter solstice. The piece is most likely to have belonged to the Unetice people, and although no written records exist, the disk does go a long way to supporting the idea that they had a complex understanding of the cycles of the night sky, and a developing understanding for other uses such as a navigation. The Unetice culture (ca. 2300– 1700 b.c.) has been cited as a pan-European cultural phenomenon, whose influence covered large areas due to intensive exchange of pottery and bronze artifacts. Intriguingly, the copper in the Nebra Sky Disk originated at Bischofshofen in Austria, while the gold was thought to be from the Carpathian Mountains. However, further study has found that the gold used in the first phase was actually sourced from the river Carnon in Cornwall, England. The tin content of the bronze was also from Cornwall. Researchers have suggested that the disk was used as a complex astronomical clock for the harmonization of solar and lunar eclipses. Obviously much more than just a simple adornment, when aligned properly and held flat, the gold bands align with the

Nebra Sky Disc

23

Fig. 3.1. Pleaides star cluster, the Seven Sisters. Spitzer Space Telescope. (Courtesy of NASA.)

spread of the sunrise and sunsets over the course of the year. The position of Pleaides perhaps assisted the user of the disk in its actual alignment. Although in modern times there are only six stars in the Pleaides visible to the naked eye, in the Bronze Age the group of stars may have been brighter, showing a seventh, and thus accounting not only for the depiction of seven stars on the disk but also for the ancient Greek name for the cluster – the ‘Seven Sisters’ (Fig. 3.1). It has been suggested that the disk was a ritual item, used by a priestly class at certain times of the year to remind people and reaffirm the movements of the heavens, the path of the Sun and Moon. This notion is supported by the provenance of the metals, which originate from all across Europe. The design, structure, and metals used would indicate that the Nebra Sky Disk was no everyday item, with a great deal of work placed in the piece beyond its visual appeal. There remains solid evidence, though, for connecting the disk with prehistoric agriculture, with the further possibility other than its link with the sowing and harvesting of the land, that the (third) golden arc underneath the crescent Moon and golden disk in fact represent a sickle.

24

3.  Other Ways the Ancients Kept Astronomical Records

Such is the importance of the Nebra Sky Disk that it was subsequently included in UNESCO’s ‘Memory of the World’ register, an international initiative launched to safeguard the documented heritage of humanity. The disk is on display in the State Museum of Prehistory in Halle, Germany.

The Dendera Zodiac The Dendera Zodiac is the name given to an interesting bas-relief found on the ceiling of a chapel in the Temple of Hathor, which is part of the Dendera Temple complex in Upper Egypt. The temple complex is situated to the south of Abydos, in what was, in ancient Egyptian times, the 6 Nome of Upper Egypt. The main temple of the complex is the Temple of Hathor, in which numerous smaller shrines/chapels are located. On the ceiling of one of the chapels dedicated to the god Osiris, where the mysteries of his resurrection were once celebrated, the Dendera Zodiac may be found. Osiris is the god of the afterlife, the underworld, and rebirth in ancient Egyptian religion. The term bas-relief or low relief (from the Italian basso rilievo) refers to a projecting image with a shallow overall depth (for example, used on coins), on which all the images are in low relief. On the lowest reliefs, the relative depth of the elements shown is completely distorted. If seen from the side, the image makes no sense at all, but from the front, the small variations in depth register as a three-dimensional image. Other versions distort depth much less. This technique requires less work, and is therefore cheaper to produce than high relief, as it requires less of the background to be removed in a carving, or less modeling required. In the art of ancient Egypt and other ancient Near Eastern and Asian cultures, and also mesoAmerica, a consistent very low relief was commonly used for the whole composition. The Dendera Zodiac is notable for its depiction of the constellations, which include the signs of the zodiac. Most of these signs would be easily recognizable by a modern-day observer, as they are depicted almost as they are today. Nevertheless, there are also several odd signs that may less easily be identified; these are represented in accordance to the sacred iconography of ancient Egypt. The Dendera Zodiac is basically a planisphere or map of the stars on a plane projection. It incorporates the 12 constellations of the zodiac, forming 36 decans of 10 days each, along with the

The Dendera Zodiac

25

planets. The decans are groups of first-magnitude stars. These were used in the ancient Egyptian calendar, which was based on lunar cycles of around 30  days and on the heliacal rising of the star Sothos (Sirius). The representation of the zodiac is somewhat unique in the fact that it takes a circular form, with more typical representations taking on a rectangular guise. The circular form is certainly unique in Egyptian art. The celestial arch is represented by a disk held up by four pillars of the sky in the form of women, between which are inserted falconheaded spirits. On the first ring, 36 spirits symbolize the 360 days of the Egyptian year. The inner circle depicts the constellations of the zodiac. Some are represented in the same Greco-Roman iconographic forms as their familiar counterparts, for example Taurus and Scorpio. Some are shown in more Egyptian form, for example, Aquarius, which is represented as the flood god Hapi (Nile God), holding two vases that gush water. Hapi was the god of the annual flooding of the Nile in the ancient Egyptian religion. In essence, the Dendera Zodiac, or the Zodiac of Osiris, is an ancient astronomical map that contains all the information necessary to calculate the journey of Earth from one zodiac sign to another for 29,920  years, which corresponds to the axial precession cycle. The Egyptian priests, responsible for what is considered one of the oldest astronomical messages left for humanity, knew the secrets of precession and the basis of their calculations is the “great year” – 25,920 years. One astrological era is equal to 1/12 of the precession of Earth’s axis and corresponds to 2160 years. An astrological era is a period of time in which the vernal equinox is in the same zodiacal constellation. According to several researchers of the Dendera Zodiac, the constellation of Cancer is the highest one, which indicates the possible time of its creation, when the point of the summer solstice was in Cancer. Egyptian priests linked Dendera to a very distant past. One of the inscriptions in the temple states that original building plans were a legacy of a “primitive early age” and were discovered in the form of antique drawings made on animal skin in the times of the followers of Horus. Horus is one of the most significant ancient Egyptian deities. He was worshipped from at least the late prehistoric Egypt until the Ptolemaic Kingdom and Roman Egypt. The chapel dedicated to Osiris was begun in the late Ptolemaic period, initially founded in 305 by Ptolemy I Soter (“the Savior”) (367–282 b.c.), creating a dynasty that was to rule Egypt for nearly 300 years. Its pronas, or portico (a porch leading to the entrance

26

3.  Other Ways the Ancients Kept Astronomical Records

of a building with a roof structure over a walkway), was added by the emperor Tiberius Caesar Divi Augusti filius Augustus  – the second Roman emperor. The addition of the pronas led French philologist and orientalist Jean-Francois Champollion (1790–1832) to date the relief to the Greco-Roman period, but this belief has been challenged. Champollion was renowned for his work as the decipherer of Egyptian hieroglyphs and one of the founding fathers of Egyptology. A fluent speaker of Coptic Egyptian and Arabic, his involvement with deciphering was a landmark in the field of study. During the early nineteenth century, French culture was being gripped by so-called ‘Egyptomania,’ a time during which Europeans were expressing a heightened interest in ancient Egypt, primarily as a result of Napoleon Boneparte’s (1769–1821) Egyptian campaign (1798–1801), which led to an extensive study of ancient Egyptian remains and culture. Bonaparte’s campaign brought to light the trilingual Rosetta stone, discovered in 1799, made from granodiorite stele, a rock not dissimilar to granite, with a phaneritic-textured intrusive rock (the microstructure of which is made up of crystals large enough to be seen by the unaided eye), which, in contrast to granite, contains more plagioclase feldspar than orthoclase feldspar. The term “plagioclase” is from the ancient Greek for oblique fracture, a reference to its two cleavage angles, and “orthoclase” is from the ancient Greek for straight fracture, because its two cleavage planes are at right angles to each other. The stone is inscribed with three versions of a decree issued at Memphis, Egypt, in 196 b.c. during the Ptolemaic dynasty on behalf of Ptolemy V (210–181 b.c.), who was the fifth ruler of the dynasty, from 204 to 181 b.c., coming to the throne at the age of five! Champollion found himself challenged not just with regard to the pronas on which the Dendera Zodiac was sited but on his interpretation of hieroglyphs generally. Scholars debated the age of the Egyptian civilization and the function and nature of hieroglyphic script, which language if any it recorded, and the degree to which the signs were phonetic (representing speech sounds) or ideographic (recording semantic concepts directly). The first known phonetic studies were carried out as early as the sixth century b.c. by Sanskrit grammarians. The term “ideograph” is often used to describe symbols of writing systems such as Egyptian hieroglyphs, Sumerian cuneiform, and Chinese characters. However, these symbols are logograms, representing words or morphemes of a particular language rather than objects or concepts.

The Farnese Atlas

27

Many scholars thought that Champollion was wrong, and that the script in question was only used for sacred and ritual functions. As such it was unlikely to be decipherable, since it was tied to esoteric and philosophical ideas and, as a consequence, did not record historical information. However, Champollion’s decipherment showed them to be wrong. He applied the work undertaken by British polymath and physician Thomas Young (1773–1829), who had made a number of notable advances in decipherment, particularly with regard to the Rosetta stone. Champollion applied Young’s approach to an obelisk inscribed in Greek and hieroglyphics, correlating the sound values to individual glyphs by applying comparisons to the names Ptolemy and Cleopatra. Champollion made the assumption that sounds (such as “t”), could be represented by two glyphs, just are they are in English with different letters (such as the hard “c” and “k”). Using this understanding, he embarked on applying the method to other hieroglyphics. Despite Champollion’s work in the field of hieroglyphics and related areas, his dating of the relief to the Greco-Roman period was challenged, with others believing it to be from a different period, that of the New Kingdom, a time also known as the Egyptian Empire, between the sixteenth century b.c. and the eleventh century b.c. The debate led the whole argument to be called the “Dendera Affair,” with French mathematician and physicist Jean-­Baptiste Joseph Fourier (1768–1830), who accompanied Napoleon Bonaparte on his Egyptian expedition, estimating the planisphere to date from 2500 b.c. Champollion, who placed the zodiac in the fourth century a.d., also had a challenge from French naturalist and zoologist Georges Cuvier (1769–1832), a man sometimes referred to as the “founding father of paleontology.” Cuvier claimed the zodiac dated from a.d.123–147. Despite the differences of opinion over its dating, there is no doubting the significance of the Dendera Zodiac, with English astronomer John H. Rogers characterizing it as “the only complete map that we have of an ancient sky.” There has been a great deal of speculation that the zodiac is the very basis on which later astronomy systems were based.

The Farnese Atlas The Farnese Atlas is a second century Roman marble copy of a Hellenistic sculpture of the Titan Atlas, from Greek mythology, kneeling with the celestial spheres, not a globe, weighing heavily on

28

3.  Other Ways the Ancients Kept Astronomical Records

his shoulders. The period in question spans 323–31 b.c., with Atlas condemned to hold up the celestial heavens for an eternity after the Titanomachy, a series of battles fought in Thessaly between an older generation of gods based on Mount Othrys and a younger generation of gods based on Mount Olympus. After evidently losing, Atlas was sentenced by Zeus to hold up the sky. In a somewhat ironic twist, Atlas, who was skilled in many scientific disciplines, is, in antiquity, credited with inventing the first celestial sphere and, in some texts even credited with the invention of astronomy itself! The Farnese Atlas was acquired by Italian Cardinal Alessandro Farnese (1520–1589), his name becoming associated with the sculpture after its acquisition and the place where it was subsequently displayed, the Villa Farnese, a mansion situated 50  km northwest of Rome. The sculpture depicts Atlas, a Titan in Greek mythology, bearing the weight of the heavens on his shoulders as a sentence from Zeus for leading the Titans into a battle against the Olympians. Not only is the work the oldest surviving sculpture depicting Atlas, but it is also the oldest known representation of a celestial sphere. The sculpture stands 2.1  m tall, with the globe showing a depiction of the night sky as seen from the outside of the outermost celestial sphere, with low reliefs depicting 41 (42 according to some sources) of the 48 classical Greek constellations identified by Ptolemy. Measuring 65 cm in diameter, the constellations include Aries the Ram, Cygnus the Swan, and Hercules the Hero. To date, the Farnese Atlas is the oldest surviving pictorial record of Western constellations. It has long been presumed to represent constellations mapped in an earlier Greek work. The text of Greek astronomer Hipparchus’ (c.190 to c.120 b.c.) long-lost star catalog may have been the inspiration for the representation of the constellations seen on the globe, which would support a proposal put forward in 1898 by eminent scholar Georg Thiele – the constellations being consistent with where they would have appeared at the time of Hipparchus. Valerio provided careful measurements of the key features of the globe, suggesting the possibility of Ptolemaic origin. However, because the globe contains no actual stars, and because the circles on the globe are drawn inexactly and ambiguously by a sculptor copying the Hellenistic model rather than by a modern astronomer, the dating of the globe remains uncertain.

4.  The Astrolabe The Revolution in Depicting the Night Sky The recording and detailing of phenomena in the night sky can be described as a time-consuming task that for some can span a lifetime  – hours of work that will eventually result in adding a small piece to the great celestial jigsaw, perhaps a quest that will never be completed. However, some would argue that it is not a task at all but a joy to be working in a field that ultimately contributes to our overall understanding of the universe in which we live, for they are the pioneers, pushing back the boundaries of our frontiers, in an attempt to unravel some of the great mysteries that still elude solving. As the ancients gazed skywards and wondered, so we do the same thing to this day, and it is only our continued commitment to astronomy and space that keeps the dreams of unlocking the secrets of the cosmos alive. From simply using one’s eyes to observe to the most powerful telescope, that which is seen can be duly remembered in one’s memory, as well as being consigned to a journal of observations, or however one chooses to document what he or she sees. The images gathered from a telescope can be stored on computer for future reference. However, understanding and subsequently relating to the sky is not a one-way street; it’s a two-way journey, and by this, we mean a frequently moving dual carriageway. The route outward is towards the night sky and beyond, into the depths of space. The route back is the ability to learn from what is being seen, and in doing so, to craft or design an object that allows us to make the journey outwards again more productive, and with more accuracy and insight. Think of it as a student/teacher relationship  – we are the students, the sky the teacher, and every time we return to the classroom, the universe, we hope to see progress in our understanding. Progress in telescopic advances is one specialized area that we can readily show advancement, but what about the means to use either one’s own eyes or a telescope more effectively?

© Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_4

29

30

4.  The Astrolabe

Fig. 4.1. John H.  Glenn and the Celestial Training Device. (Courtesy of NASA.)

Although there have been many tools at the disposal of the astronomer throughout the centuries, some creations deserve a special place in history, as they led to a greater understanding of our universe. One such instrument is the astrolabe, the earliest surviving model of which dates from a.d. 927 or 928. The name has its origins from the Greek words astron and lambanien, meaning “the one who catches the heavenly bodies.” Centuries later, the use of the astrolabe would continue to find other uses that couldn’t even be dreamed of during the early formative periods in history. It’s interesting to ponder just how the early designers and constructors of the astrolabe would have felt to see their concept eventually become an actual tool in a different guise, the “Celestial Training Device,” to assist the likes of John H. Glenn, Jr., (1921–2016), with his astronaut training ahead of his landmark venture into space to orbit Earth in 1962 (Fig. 4.1).

History of the Astrolabe The astrolabe was crafted and used for centuries in European and  Islamic cultures, the modern-day equivalent of a “smart-­ device” with a range of capabilities. Unlike some of the less useful

History of the Astrolabe

31

applications on the so-called “smart-devices” of this century, the astrolabe offered a range of features, all of which had a necessary purpose and was not just an ancillary role. The astrolabe is a multi-functional device used by astronomers and navigators to measure the altitude above the horizon of a celestial body, day or night. As well as being an accurate timepiece, the astrolabe can be used to identify stars or planets, to determine local latitude given local time (and vice versa), to survey, to triangulate, and generally be as essential as the legendary Swiss Army knife. The astrolabe came into being during times of economic prosperity and remained popular throughout the eighteenth century. Described by some as an elaborate inclinometer or clinometer (an instrument used for measuring angles of slope or tilt, elevation, or depression of an object with respect to gravity’s direction), the importance of the astrolabe cannot be underestimated, with the roots of its birth firmly associated with the early development of astronomy. Its ability to determine latitude on land or calm seas is noteworthy, and while probably not as reliable accuracy-wise on the deck of a ship being thrown around in heavy seas, the principle design of the astrolabe could and was upgraded to compensate for this, with the mariner’s astrolabe subsequently developed to tackle such the problem. Strong evidence exists that the astrolabe’s starting point is around the time of Greco-Roman mathematician, astronomer, geographer, and astrologer Claudius Ptolemy (a.d. 100 to c.170). Ptolemy left records suggesting he used a three-dimensional instrument similar to the astrolabe to make his calculations. Although this would seem to credit Ptolemy, it is reasonable to believe that the instrument existed further back in history, with the documentation of such an instrument perhaps made on papyrus, which, over time, has since decayed. One of the most popular but inaccurate stories proposes that Ptolemy invented the astrolabe when a donkey that he was riding trod on his star globe and flattened it! Of the records that do exist of the early astrolabe, it is believed that one of the early versions was invented in the Hellenistic civilization by Apollonius of Perga between 220 and 150 b.c. The Hellenistic period is the period of Mediterranean history between the death of Alexander the Great in 323 b.c. and the emergence of the Roman Empire, as signified by the Battle of Actium in 31 b.c. This battle was the decisive confrontation of the Final War of the Roman Republic, a naval engagement between Octavian and the combined forces of Mark Antony and Cleopatra on September 2.

32

4.  The Astrolabe

Octavian’s victory enabled him to consolidate his power over Rome and its dominions. The invention of the plane astrolabe is often wrongly attributed to the daughter of Greek scholar and mathematician Theon of Alexandria (a.d. c.335 to c.405), who wrote a detailed treatise on the astrolabe. His daughter Hypatia (a.d. c.350–415), herself an astronomer and mathematician, could not possibly be the inventor, as such an instrument had already been in use 500 years before she was born. The misunderstanding stems from a letter written by a pupil of Hypatia’s named Synesius, which mentions that Hypatia had taught him how to construct a plane astrolabe. However, there is a great difference between teaching about such an invention and actually inventing the astrolabe itself; in the letter there is no mention of Hypatia being the inventor. The earliest extant treatise on the astrolabe was written around a.d. 550, by Alexandrian philologist John Philoponus. Also known as John of Alexandria, he wrote a considerable number of works, and some of his observations earned him the reputation of being quite a controversial writer for his original thoughts on established beliefs. His treatise on the astrolabe, which wasn’t controversial, came at a time when the device was being widely used throughout the Byzantine period in the Greek-speaking world, which represented the continuation of the Roman Empire in its eastern provinces during late antiquity and the Middle Ages. Among those known to have also written a treatise on the astrolabe is Mesopotamian scholar and bishop Severus Sebokht (575–667), writing in the Syriac language (a major language throughout the Middle East from the fourth to the eighth centuries) in the mid-seventh century. This major work contains 25 chapters and provided detailed explanations of the movements of heavenly bodies. The introduction of his treatise refers to the astrolabe as being made of brass, indicating that metal astrolabes were known in the Christian East well before they were developed in the Islamic world or in the Latin West. This is an important point when considering the history of the astrolabe and its evolution and the questions surrounding its very invention. The astrolabe, which translates roughly to “star-taker” in Greek, traveled out of Europe and into the Islamic world during the eighth century. This translation for the word astrolabe can be traced back through medieval Latin to the Greek word astrolabes, from astron “star” and lambanein “to-take.”

History of the Astrolabe

33

Astrolabes were further developed in the medieval Islamic world, a period in history of significant cultural, economic, and scientific flourishing, and which is traditionally viewed as spanning the eighth to the fourteenth century. During this time, Muslim astronomers introduced angular scales to the design, adding circles indicating azimuths on the horizon. The astrolabe was widely used throughout the Muslim world, chiefly as a tool to find the direction of prayer towards Mecca – known as the Qibla – as well as the five times of prayer required throughout the day, as stated in the Quran. Mathematician and astronomer Muhammad al-Fazari (died 796 or 806) is credited as being the first person to build the astrolabe in the Islamic world. Along with his father and fellow astronomer Yaqub ibn Tariq, he helped translate the Indian astronomical text by Brahmagupta, who was also the author of another work on mathematics and astronomy. In the tenth century, Persian astronomer al-Sufi (903–986) first described over 1000 different uses for an astrolabe, including astronomy, astrology, navigation, surveying, timekeeping, and prayer. The mathematical background to the astrolabe was established by Muslim astronomer, astrologer, and mathematician Albetenius (c. 858–929), in his treatise Kitab az-Zij, which was translated into Latin by Plato Tiburtinus (De Motu Stellarum). Albetenius is sometimes referred to as the “Ptolemy of the Arabs” and is widely considered the greatest and best-known astronomer of the medieval Islamic world. His Kitab (“Book of Astronomical Tables”) was a major work based on Ptolemy’s theory, with descriptions of a quadrant instrument in the text. The book went through many translations, with Italian astronomer and translator Plato Tiburtinus’ version apparently being the first to translate information on the astrolabe from Arabic into Latin. The earliest description of the spherical astrolabe dates back to Persian mathematician and astronomer Al-Nayrizi (865–922), who from 892 to 902 also compiled a book on astronomical tables, with further work on atmospheric phenomena. His treatise on the spherical astrolabe is very elaborate and to date qualifies as the best Persian work on the subject, with his work divided into four books: • Historical and critical introduction. • Description of the spherical astrolabe; its superiority over plane astrolabes and all other astronomical instruments. • Two books of applications.

34

4.  The Astrolabe

In the twelfth century, Iranian mathematician and astronomer Sharaf al-Din al-Tusi (c.1135 to c.1213) invented the linear astrolabe, sometimes referred to as the “staff of al-Tusi.” The instrument comprised “a simple wooden rod with graduated markings but without sights. It was furnished with a plumb line and a double chord for making angular measurements and bore a perforated pointer.” Although the construction was widely known in Al-Andalus – a medieval Muslim territory that in its early period occupied most of Iberia, today’s Portugal and Spain  – outside of this domain, it did not gain a great deal of popularity. The instrument while not overly coveted was an important step in the evolution of the astrolabe, for if versions are to be built and trialed, many processes and ideas must be explored in order that advancements are made. The geared mechanical astrolabe was invented by Muhammad ibn Abi Bakr al Ibari around 1221 or 1222. On its front is the astrolabe, linked to a calendar by gear train; on the reverse is a disc showing the phases of the Moon. In recognition of Al-Tusi, an asteroid discovered by American astronomer Henry E. Holt (born 1929) at Palomar Observatory in 1990 was named in his honor. Between 1989 and 1993, Holt, a prolific discoverer of minor planets and comets, discovered an incredible 700 minor planets. Among his finds, which include 7058 Al-Tusi, which he sighted on September 16, 1990, Holt also discovered the potentially hazardous asteroid 4581 Asclepius, an Apollo group body that makes close orbital passes with Earth. Discovered on March 31, 1989, by Holt and fellow astronomer Norman Gene Thomas (born 1930), Asclepius is named after the Greek demigod of medicine and healing, with geophysicists estimating the asteroid would release energy comparable to the explosion of a 600-megaton atomic bomb were impact with Earth to occur. With an estimated measurement of around 300 m, its discovery was made 9  days after its closest approach to Earth. On March 24, 2051, Asclepius is expected to pass Earth at a distance of just 1,840,000 km, slightly further away than its pass in 1989 of 684,000 km. Along with Asclepius, Holt and Thomas also discovered near-Earth asteroid 4544 Xanthus, also of the Apollo group, measuring 1.3 km in diameter. Herman Contractus (1013–1054), the abbot of Reichman Abbey, examined the use of the astrolabe in Mensura Astrolai during the eleventh century. Also known as Hermann of Reichenau, a composer, mathematician, and astronomer, he wrote several works

History of the Astrolabe

35

on geometry and arithmetic, with his contribution to astronomy including instructions on how to construct an astrolabe. In the last half of the thirteenth century, French scholar Peter Peregrinus of Maricourt wrote a treatise entitled Nova compositio astrolabii particularis on the construction and use of a universal astrolabe. Aside from this work, he was known for conducting experiments on magnetism and was responsible for writing the first extant treatise describing the properties of magnets. The construction method Peregrinus outlined for the astrolabe meant it could be used at a variety of latitudes without changing the plates. Like other inventors, the influence interest in his astrolabe did not amount to much, with his work in the field of magnetism far outweighing any of his work on the astrolabe. His De magnete was a very popular work from the Middle Ages onwards, witnessing a large number of manuscript copies. English author Geoffrey Chaucer (1343–1400) compiled A Treatise on the Astrolabe for his son in 1391, which is thought to have been mainly based on the work of astrologer, astronomer, and mathematician Mashallah ibn Athari (c.740–815) or Ibn alSaffar (died 1035). Ibn Athari was among those who introduced astrology and astronomy to Baghdad in the late eighth and ninth centuries. He served as a court astrologer for the Abbasid caliphate (the third of the Islamic caliphates to succeed the Islamic prophet Muhammad), and wrote numerous works on astrology in Arabic. Mashallah’s treatise on the astrolabe is the first known of its kind, later translated from Arabic into Latin (De Astrolabii Compositione et Ultilitate). In Chaucer’s treatise on the astrolabe, he describes both the form and the proper use of the instrument, with his technical ability and understanding of the subject as excellent as his other work. His treatise is also considered by many to be the oldest work in English to have been written on such an elaborate scientific instrument. Chaucer’s clarity on the description and operation of the astrolabe is remarkable, with deserved respect given in the relaying of information of such a difficult ‘concept,’ so much so that modern-day readers may find the intricacy of the detail a little hard to comprehend. Although there remains great uncertainty as to exact source of Chaucer’s work, there seems to be evidence to support an elaboration on the Latin translation of Mashallah’s work called Compositio et Operatio Astrolabii. However, some have argued

36

4.  The Astrolabe

that Chaucer’s work was indeed based upon the best-known work of Ibn al-Saffar, a text that was in active use until the fifteenth century and directly influenced the work of Kepler. There is evidence to suggest that the same source, either Mashallah’s work or that of Ibn al-Saffar, was translated by French astronomer and astrologer Pelerin de Prusse, among others. While little is known about de Prusse, his treatise Practique de l’Astrolabe is the earliest known treatment of the work in French, and is among the earliest, if not the earliest, in a European vernacular language. Written in 1362 at the behest of Charles V, it remains an important early example of technical and scientific writing. The first printed book on the astrolabe was the Composition and Use of the Astrolabe by Christian of Prachatice (c. 1370–1439), also using Mashallah’s work as a basis, although much of the work is relatively original. In fact, Christian wrote numerous treatises in the fields of astronomy, mathematics, and medicine. In 1370, the first Indian treatise on the astrolabe was written by Jain astronomer Mahendra Suri. Jain refers to the ancient, non-­theistic, Indian religion that began around the sixth century b.c. with a strong influence on mathematics. His work Yantraraja was written in Sanskrit around a.d. 1370. The astrolabe was introduced into India at the time of Firuz Shah Tughluq (1309–1388), whose reign as sultan lasted from 1351 to 1388. A simplified astrolabe, known as a balestilha, was used by sailors to get an accurate reading of latitude while out at sea. The use of the balestilha was promoted by Prince Henry (1394–1460) while out navigating for Portugal. In navigation, the instrument is also called a cross-staff and was used to determine angles, for instance, the angle between the horizon and the pole star Polaris or the Sun, to determine a vessel’s latitude, or indeed the angle between the top and bottom of an object to determine the distance to said object if its height is known. It can also determine the height of the object if the distance is known, and the horizontal angle between two visible locations to determine one’s point on a map. Also known as Jacob’s staff when used for astronomical observations, the instrument was also referred to as a radius astronomicus. There remains some doubt over the origin of the name Jacob’s staff, with some tying it to the biblical patriarch Jacob, others to its resemblance to the constellation of Orion, which was referred to by the name of Jacob on some medieval star charts. Another possible explanation for what was originally a single pole device, before its later addition of a staff and cross piece, is that of the Pilgrim’s staff, the symbol of St. James (Jacobus in Latin).

Construction of the Astrolabe

37

Construction of the Astrolabe The astrolabe was a marriage of the planisphere and the diptra – effectively, an analog calculator capable of working out several different kinds of problems in astronomy. As devices from different regions and time periods could vary widely, depending on their intended purpose and who made them, the astrolabe could be as small as a teacup saucer or as large as a trash can lid, with various materials used in their construction, from wood to brass. The astrolabe was developed in three distinct varieties: • The spherical astrolabe. In this case, the observer’s horizon is drawn on the surface of the globe, mounted with a freely rotating spherical lattice work or ‘spider’ representing the celestial sphere. Only a few examples of this type of astrolabe have been preserved. • The planisphere astrolabe. This is the most common form of the instrument. Both the celestial sphere and the observer’s horizon are projected onto one or more plane surfaces by means of the stereographic projection. This type proved to be the most popular and the most convenient to use. • The linear astrolabe. In the most abstract version of the astrolabe, the celestial sphere and the observer’s horizon are projected on to a line. Although the simplest of all forms, being nothing more than a finely graded rule, its rules of operation proved to be so impractical that no examples have been preserved. Regardless of construction method, all three types shared a similar structure, which basically consists of a circular stack of sliding features all embedded within a disk called a mater (mother). The mater is deep enough to hold one or more flat plates called tympans, or climates. A tympan is made for a specific latitude and is engraved with a stereographic projection of circles, which denote azimuth and altitude, representing the portion of the celestial sphere above the local horizon. The rim of the mater is typically graduated into hours of time, degrees of arc, or indeed both. Above the mater and the tympan is another circular feature known as the rete, which is a framework bearing a projection of the ecliptic plane and several pointers indicting the positions of the brightest stars. The rete is free to rotate. Generally, the pointers are exactly just that, simple points offering the locations of certain well-known stars in the sky, but depending on the skill of the

38

4.  The Astrolabe

craftsman, they can in some instances be very elaborate and quite artistic in nature. Some of the pointers are in the shape of balls, stars, snakes, hands, leaves, and even dogs’ heads. The names of the indicated stars were often engraved on the pointers in Arabic or Latin. In some cases, a narrow rule or label is in place, which rotates over the rete, and may be marked with a scale of declinations. The general purpose of the rete is that of a star chart. When the rete is rotated, the stars and ecliptic move over the projection of the coordinates on the tympan. One complete rotation corresponds to the passage of a day. The reverse of the mater is often engraved with a number of scales that can be used for a number of applications of which there is variance, with different designers applying their own “stamp” as to how they eventually developed the reverse side, perhaps as directed or at their own discretion. These might include curves for time conversions, or perhaps a calendar for converting the day of the month to the Sun’s position on the ecliptic. Some also have trigonometric scales. Attached to the back face is the alidade or turning board, which allows one to sight a distant object and use the line of sight to perform a task, often the starting point of a calculation. At one time, some alidades, particularly those used on graduate circles such as on astrolabes, were also called diopters. There are various constructions of the alidade, one such design being the creation of astronomer Johannes Hevelius (1611– 1687) who, following in the footsteps of fellow astronomer Tycho Brahe (1546–1601), catalogued star positions. Although Hevelius did have access to telescopic sights that were being used by astronomers in other countries, he chose to use naked-eye observations for his positional instruments. An alidade is often incorporated into more modern instruments, such as the theodolite. The alidade is the part of the theodolite that rotates around the vertical axis, and that bears the horizontal axis around which the telescope goes up and down. In the sextant, the alidade is the arm that turns, carrying a mirror and an index to a graduated circle in a vertical plane, more commonly referred to in recent times as the index arm. The very nature of its potential application has seen alidade tables being used in fire towers for sighting forest fires.

5. Supernovae Documenting Explosions in the Heavens When a significant event in astronomy occurs, the attention and gaze of the world is captured. Modern-day technology with so many “eyes” eagerly awaits that which perhaps previously went unseen. The supernova (SN) of 1054 is important as it reflects just how the event was observed globally during a time when the “eyes” of the world were fewer. The supernova brought to the fore just how the world perceived such a happening at the time. Many civilizations would probably have not been known about or been as well documented in history if such events did not occur, with their lives and cultures perhaps not undergoing as much scrutiny if there was no possible link seen to such events. SN 1054 and other supernovae have time and time again brought the records of many nations to the fore, probably in a way that only another astronomical phenomenon, comets, has achieved. In perhaps equal measures, for the good of the world but not for the privacy of a tribe or nation, the way in which ancient civilizations lived has been brought to the attention of others thousands of miles away, and in turn a greater understanding of the culture, the people, and their social and belief systems has resulted. When we embrace how others perceive the world, a balance is struck against our own understanding, and it is through the heavens, which are viewed by so many different peoples from so many different backgrounds, that we can pool our collective knowledge, just as ancient stellar cartographers in different countries drew the same maps of sky looking at the same stars but applying different methods to how they presented their findings. Supernovae certainly create an impact when acknowledging all the different types of astronomical phenomenon that are known to exist. However, the word supernova does not carry a single definition. Different types of stars are associated with such an explosion, with different kinds of remnants being produced.

© Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_5

39

40

5. Supernovae

There are two main types of supernovae, Type I and Type II. Broadly speaking, a Type I Supernova is a star that accumulates matter from a nearby neighbor until a runaway nuclear reaction ignites. Type I Supernovae are generally thought to originate from white dwarf stars in a close binary system. As the gas from the companion star accretes onto the white dwarf, the white dwarf becomes progressively compressed, and eventually this triggers an unstoppable nuclear reaction that leads to an outburst. A Type II Supernova occurs with a star that is running out of nuclear fuel and is collapsing under its own gravity. For a Type II Supernova to explode, the premise is completely different from that of a Type I. Here, the star in question must be several times more massive than our Sun (estimates run from 8 to 15 solar masses). Like the Sun, it will eventually run out of hydrogen and then helium at its core. However, despite this state, the star will still possess enough mass and pressure to fuse carbon. Gradually, as the heavier elements build up at the center, each in turn become layered, with elements becoming lighter towards the outside of the star. The star core will gradually build in mass until it surpasses a certain level known as the Chandrasekhar limit, named after astrophysicist Subrahmanyan Chandrasekhar (1910–1995), and it is at this point that the star begins to implode. As this occurs, the core begins to heat up and becomes denser, with the implosion eventually rebounding back off the core, expelling the material into space as a supernova. Stars much more massive than our Sun (around 20–30 solar masses) might not explode as a supernova, instead collapsing to form black holes. As part of an attempt to understand and develop our knowledge of supernovae, astronomers have classified them according to their light curves and the absorption lines of different chemical elements that appear in their spectra. If a supernova’s spectrum contains lines of hydrogen, it is classified as a Type II; otherwise, it is classified as a Type I. From Type I and Type II, subdivisions occur according to the presence or lack of presence of other elements or the shape of the light curve. Type I supernovae are subdivided on the basis of their spectra, with Type Ia showing a strong ionized silicon absorption line. Types Ib and Ic are the subdivisions where the strong ionized silicon absorption line does not exist. However, Type Ib will show strong neutral helium lines, while Type Ic will not. Although the light curves right across the Type I are generally similar, the only difference is a brighter peak luminosity for Ia.

The Supernova of 1054

41

Type II follow the same subdivisions with regard to spectra. Although most Type II supernovae show very broad emission lines, which indicate expansion velocities of many thousands of kilometers per second, some have relatively narrow features in their spectra. This type is known as Type IIn, the ‘n’ standing for ‘narrow.’ Type IIb describes a supernova that appears to change type, normally exhibiting a combination of features associated with Type II and Type Ib. A further subdivision for Type II supernovae reflects changes of status of the associated light curve. Type II-P refers to a supernova where the light curve shows a distinct “plateau” after peak brightness; this means the visual luminosity stays relatively constant for several months before a decline, which was evident after the initial outburst of brightness resumes. Type II-L denotes a lack of a plateau, the ‘L’ denoting ‘Linear,’ whereby the light declines steadily after the explosion. Swiss astronomer Fritz Zwicky (1898–1974) defined additional supernovae classifications that did not fit into any of the categories mentioned, naming them Types III, IV, and V. On average, a supernova will occur about once every 50 years in a galaxy the size of the Milky Way. In other words, a star explodes every second or so somewhere in the universe, and some of those aren’t too far away from Earth. About ten million years ago, a cluster of supernovae created the “Local Bubble,” a 300-light-year-­ long, peanut-shaped bubble of gas in the interstellar medium that surrounds the Solar System. The Local Bubble, or “Local Cavity,” is the result of a supernovae that exploded within the past 10–20  million years and remains in an excited state. Situated in the Interstellar Medium (ISM), the matter and radiation that exist in space between systems in the galaxy, it contains the Local Interstellar Cloud (LIC), which in turn contains the Solar System. This cavity is situated in the ISM of the Orion-Cygnus Arm in the Milky Way, a minor spiral arm of our galaxy. Also present with the LIC is the G-Cloud Complex, a further interstellar cloud located alongside the LIC.

The Supernova of 1054 On July 4, 1054, a great supernova was observed around the globe, the actual explosion having taken place many thousands of years ago, before the light from it actually reached Earth. The remnant of

42

5. Supernovae

Fig. 5.1.  SN 1054, the Crab Nebula. (Courtesy of Nordic Optical Telescope)

the outburst, the Crab Nebula, is among the most-studied objects outside of our Solar System. At a distance of 4000 light years, much of the supernova’s energy had diminished through space before it reached Earth. However, the brilliance of the outburst in our skies would have been remarkable, appearing six times as bright as Venus would have appeared in the sky, visible even at high noon. The star’s brilliance meant that it was visible during the day for nearly 3 weeks. The supernova was so strong that if it had occurred within 50 light years of Earth, all living things on the planet may well have been destroyed (Fig. 5.1). The star that went supernova was so massive that it left only a rapidly rotating ball of neutrons, a pulsar. The Crab pulsar measures 17–19 km across, but has a mass greater than the Sun. The pulsar ‘pulses,’ or spins, 30.2 times per second. The visible light from the supernova represented itself as a bright, glowing star that remained on view for 2 years. Reports and documentation of the sightings were recorded in China, Japan, Korea, and modern-day Iraq, while questions remain over the interpretation given to possible sightings elsewhere, perhaps the most curious of which is the oral tradition of aboriginal Australians. Likewise, there are references from European sources recorded in the fifteenth century, and perhaps a pictograph associated with the ancestral Puebloan culture found near the Penasco Blanco site in New Mexico.

The Supernova of 1054

43

The event was recorded in contemporary Chinese astronomy, with references to the supernova to be found in a later (thirteenth century) Japanese document from the Arab world. The Chinese and Japanese recorded the appearance as a “guest star” in their skies. Several references to its sighting were also made across Europe and were also, more interestingly, the subject of Native American cave paintings. During the time of the explosion, it was the Dark Ages across Europe, so called because relatively few written records have survived. Added to that, scholars both there and in the Middle East were more interested in the reliable and seasonable patterns of the incorruptible heavens, and less so in the unpredictable appearance of comets and “guest stars.” It does seem rather odd, though, given the fact that this new star was on show for nearly 2 years, that documentation is so scarce, indeed, virtually non-existent. The remnant of Supernova 1054 is located near Zeta Tauri in Taurus the Bull. Zeta Tauri is the name designated in 1603 by the Bayer system introduced by German astronomer Johann Bayer, (1572–1625), its corresponding Flamsteed designation, after John Flamsteed, is 123 Tauri. Zeta Tauri is an eclipsing binary system comprised of two components: the larger star A and smaller star B. At a distance of 440 light years, each star follows a circular orbit of nearly 133 days. Zeta Tauri A is an enormous star with more than 11 times the mass and five to six times the radius of our Sun. Zeta Tauri B has a mass of about 94% that of our Sun and is classed as a neutron star or a white dwarf. No matter how the “guest star” was perceived or interpreted many years ago, it would have had a prominent position in the skies and would have been as easily sighted then as it would be today from many countries, a sight that during the 2  years that it was on view caught much attention, being recorded and documented in many guises. However, with regard to some documented evidence, the recorded outburst and its associated records don’t always give a clear picture of the event. Time after time, discrepancies arise that seem to challenge the information, with much conflict over calendar dates and positional data. Surely, an event as dramatic as a supernova should make for clear and concise reporting, much as the arrival of a bright comet would. At the time, unless given extreme circumstances, there would have been no other astronomical event to overshadow it or create confusion. In many aspects, the position of the “guest star” and the Crab Nebula remnant positions are called into question.

44

5. Supernovae

Chinese and Japanese Records During the time of its outburst, Chinese records suggest that the supernova was brighter than all of the stars and planets, with only the Sun and Moon surpassing the supernova for luminosity. The 1054 supernova appeared during the reign of the Emperor Renzong (1010–1063) of the Song Dynasty (960–1279). Emperor Renzong was the longest reigning Song dynasty emperor, his governance spanning 41  years. The year 1054 is recorded in Chinese documents as “the first year of the Zhihe era,” “Zhihe” being the era name used during the reign of Emperor Renzong. Some of the Chinese accounts of the supernova are well preserved and include great detail, the oldest of which survives from the Song Huiyao Jigao (“Song Government Manuscript Compendium”) and Song Shi (or “History of Song”), historical works in which the extant text was redacted perhaps within just a few decades of the event. Song Huiyao Jigao is a collection of Song dynasty writings (collected during the Qing dynasty, the last imperial dynasty of China and Mongolia) comprised of 366 chapters covering many topics, from crime and punishment to military matters. Song Shi is one of the official Chinese historical works known as the TwentyFour Histories of China. Comprised of 496 chapters, it is the largest of the Twenty-Four. Later records also exist of the event; these were redacted in the thirteenth century and which may or may not have direct links with older documentation. The Song Huiyao Jigao is itself an extract from a preserved portion of the Yongle Encyclopedia. In 1809, the extract was taken from the encyclopedia and re-published. The Yongle Encyclopedia, or Yongle Dadian (“Great Canon of Yongle”), is a partially lost Chinese Ieishu (“category books”), encyclopedia commissioned by the Yongle emperor (1360–1424) of the Ming dynasty in 1403, with the work completed in 1408. The Yongle emperor was the third emperor of the Ming dynasty, ruling from 1402 to 1424. Approximately 600 Ieishu were compiled from the early third century until the eighteenth century, of which only 200 have survived. In the true sense, these “category books” aren’t quite the same as what we term encyclopedias, but the general translation of the word Ieishu is close. It is worth noting that the Yongle Encyclopedia in its entirety was a work of mammoth proportions, so large and with such a wide and all-encompassing spectrum of topics it was unsurpassed in its magnificence until the introduction of Wikipedia on September 9, 2007, nearly six centuries later!

Chinese and Japanese Records

45

Another book covering the same period of the Song dynasty is the Xu Zizhi Tongjian Chanbian (“Long compilation of the continuation of the Zizhi Tongjian”). Written by historian Li Tao (1115–1184), in 1183, who devoted no less than four decades of his life to compiling the work, the Xu Zizhi Tongjian Chanbian is a monumental book chronicling the history of the Northern Song (960–1127), comprised of 980 chapters. Within this book lie the oldest Chinese testimonies relating to the observation of the guest star. Rediscovered in 1970 by the specialist in Chinese civilizations Professor Ho Peng Yoke (1926–2016), he and fellow researchers were able to translate wording documenting the appearance of the guest from the Liao dynasty (also known as the Khitan Empire), an empire that ruled in the area of northeastern China from 907 to 1125. The book in question, the Qidan Guo Zhi (“Records of the Khitan Empire”), was compiled by Ye Longli in 1247, written in the Southern Song dynasty and published between 1265 and 1274, during the time of Emperor Duzong’s reign. The book is comprised of 27 chapters about the Khitan people. It includes various astronomical notes, some of which are clearly copied from the Song Shi. Three accounts collectively taken from Song Huiyao Jigao and Song Shi are apparently related because they describe the angular distance from the guest star to Zeta Tauri (the closest star to the guest star) as “perhaps several inches away”; though this seems conclusive evidence that the guest star is SN 1054, there is apparent disagreement about the date of appearance of the guest star. The term “perhaps a few inches” is one that has also brought some attention. This phrase is relatively uncommon in Chinese astronomical documents but stands out as a major part of the description used as to the relative reference points with regard to Zeta Tauri and the guest star. However, although none of the three references correspond, transcription error may well be to blame for the lack of uniformity on dates. The way in which the days were recorded relate to the sexangenary cycle, also known as the Stems-and-Branches or ganzhi, a cycle of 60 terms, each corresponding to 1 year, thus a total of 60 years for one cycle. This was used for reckoning time in China and the rest of the East Asian cultural sphere. The sexangenary cycle was apparently used as a means of recording days in the first Chinese written texts and applies to the recording of the guest star. Although that discrepancy can in part be answered by a transcriptional misinterpretation, the next cannot. The description of the guest star’s location is “to the southeast” of Tianguan, ­“perhaps several inches away,” but this cannot be correct, as the

46

5. Supernovae

Crab Nebula is not situated to the southeast but to the northeast of Zeta Tauri. Tianguan, meaning “Celestial Gate,” is the official name for Zeta Tauri along with other alternative names for the star including Zeta Tau, Tien Kwan, and Zet Tau. If all the available elements suggest that the star of 1054 was a supernova, and that in the area next to where the star was seen there is a remnant of a supernova that has all the observable characteristics expected of an object of that age, the one major problem remains the discrepancy over its position in the sky. The new star is described as being to the southeast of Zeta Tauri, while the Crab Nebula is to the northeast. Could this be just another error in translation, a simple oversight? Ho Peng Yoke suggested that the Crab Nebula was not the product of the explosion of 1054 but the true remnant was to the southeast, as indicated in several other Chinese sources. Is it possible that the naming of Zeta Tauri as the reference star is incorrect? On the morning of July 4, 1054, the star Zeta Tauri was not bright enough and too low on the horizon to be visible. If the guest star, which was located close to it, was visible, it is only because its brightness was comparable to Venus. However, there was another star, brighter and higher on the horizon, which was possibly visible, Beta Tauri. If that were the star in question, discounting Zeta Tauri, the Crab Nebula would be positioned to the southeast. That would rectify the positional inaccuracies, making both the position of the guest star and the subsequent Crab Nebula correspond. Furthermore, because of the angles involved that morning that kept Zeta Tauri near or below the horizon, with the more prominent aspect of Beta Tauri clearly visible, over the coming days it would have become apparent under the greatly improved visibility of the arrangement that the guest star was in fact closer to Zeta Tauri than Beta Tauri, and that the directional use of term “southeast” used for the first star was kept in error. The duration of visibility is explicitly mentioned in Chap. 12 of Song Shi, and with slightly less accuracy in Song Huiyao Jigao. The last sighting documented was on April 6, 1056, after a total period of 642 days. Chapter. 12’s reference to the guest star is generally less concerned with its appearance than with its disappearance, as if perhaps that had more significance. According to Song Huiyao Jigao, the visibility of the guest star was for only 23 days, but this is interpreted as daytime observations only. Although the surviving records focus on the astrological aspect of the guest star, there remains the important information of the star by day and by night.

The Arab World

47

Further referencing can be found in the Wenxian Tongkao (“Comprehensive Examination of Literature”), compiled by historical writer and encyclopedist Ma Duanlin in 1317. The Wenxian Tongkao is made up of 348 volumes and was the first East Asian source that came to the attention of Western astronomers. Translated by French engineer and sinologist Edouard Constant Biot in 1843, the guest star with its position to the southeast, plus the general fading from view as the star dimmed, are mentioned. Biot is credited with useful astronomical translations, most notably associating the Crab Nebula with a supernova that was observed by the Chinese, which is no mean feat, considering the many variables involved with deciphering such texts. The oldest and most detailed account of SN 1054 from historical Japanese records is that of the diary of Japanese poet, calligrapher, and scribe, Fujiwara Sadaie (1162–1241), better known as Fujiwara no Teika, after whom the diary is entitled. Considered as one of the greatest Japanese poets, his influence was extensive across Japan. The diary records the sighting of the guest star, which it would appear he accidentally observed while observing a comet in 1230. This prompted him to search for the evidence of other guest stars, among them SN 1054, SN 1006, and SN 1181. It is important to remember that when considering the presence of a guest star, there is the possibility through translation that this may well refer to an object of luminous quality, not directly to a star as we would consider it. Another work is the Ichidai Yoki, a sort of chronicle, a collection of papers, which gives a description very similar to that given by Fujiwara no Teika, although the details are rather fragmented, with the short work also containing many typographical errors. Nonetheless, it is still a credible reference to SN 1054. A similar yet even briefer account is in the Dainihonshi (“Great History of Japan”), which is comprised of 397 scrolls in 226 volumes, and 5 index scrolls. Here, once again, there is description of guest stars, but with much more detail afforded to the observations of the supernovas of 1006 and 1181 than that of 1054.

The Arab World As established, SN 1006 was considerably brighter than SN 1054, with SN 1181 considerably fainter than both. Although no records have survived of SN 1181, perhaps because of its faintness, or

48

5. Supernovae

subsequent smaller collection of documents that have been lost through time, SN 1006 and SN 1054, respectively, do have corresponding records, although in the case of the latter, only one significant account has come to light. It wasn’t until 1978 that the account was found, written by Arab Nestorian Christian Physician Ibn Butlan (1038–1075), who lived in Baghdad during the so-called Islamic Golden Age, a period of great economic, cultural, and scientific flourishing in the history of Islam. Transcribed in the Uyun al-Anba (loosely translatable as “Sources of News of Classes of Physicians”) – a work on detailed biographies of physicians compiled by Ibn Abi Usaybi (1203–1270), himself a physician – a passage within the text refers to an epidemic that has occurred when a spectacular star appeared in [the zodiac star] Gemini 446. There is also a reference to the year 447 and to 445. The text regarding 446 continues by mentioning the deaths and subsequent burials in that autumn of 14,000 people in Constantinople, with the summer of 447 seeing the majority of the Fostat people and foreigners perish. Fostat, or Fustat, was the first capital of Egypt under Muslim rule, currently part of old Cairo. The text regarding 445 mentions the river Nile being low. The three years cited (446, 447, and 448) refer, respectively, to April 23, 1053, to April 11, 1054; April 12, 1054 to April 1, 1055; and April 2, 1055 to March 20, 1056. This would seem conclusive for the document to indeed be referring to SN 1054, albeit for the positional information that places it in Gemini, not Taurus. However, given axial precession, the eastern part of the constellation Taurus would have been covered by Gemini, which would seem to equate given the time period.

Native American Because of the duration of its appearance and its general brightness during that period, ample opportunity would have arisen for civilizations across the world to make a record of Supernova 1054’s presence, either in an early form of writing or by drawing an image. It does seem more than plausible that such an event was captured globally and by different means, including the Native American artwork in White Mesa, Arizona. The interpretation of cave artwork can be described as an art in itself, an art naturally seen through a scientific leaning, but one that also lends itself to other possibilities in terms of what is  actually being depicted, and what message, if any, it seeks to

Native American

49

convey. Also, to question why the artist chose that particular sight to record, given the many other potential ‘sitters’ of the time. One, with a degree of trepidation, must assume the artist captured the image because either other images had already been captured in various guises throughout the seasons or what was being observed was a rarity, a one-off, something that had not been sighted before. However, was too much being read into this specific artwork? The notion that the painting, along with another painting in the Navaho Canyon, also in Arizona, represented that of SN 1054 started when William C. Miller (1910–1981), a photographer based at Palomar Observatory, first published images of the two cave paintings in 1955. The paintings depict what looks like a crescent moon and a star. Along with evidence to support the now known fact that both sites were inhabited in 1054, Miller pointed out that both viewing locations afforded an unobstructed view of the eastern sky, where the supernova was located. Further calculations also suggested that the SN 1054 would have appeared in the sky with a waning crescent moon, just as the paintings depicted. However, Miller recognized that his findings were going to be open to interpretation and scrutiny, and had the foresight to acknowledge that the evidence presented was circumstantial. Miller’s findings attracted a great deal of interest, so much so that over the years that followed, other paintings were discovered across the Southwest, all depicting the same scenario, and with it, momentum grew that the connection Miller had made did have credence. With the new discoveries quickly linked with the Crab Nebula, Miller’s theory continued to hold water for many years until Edwin Charles Krupp (born 1944), an astronomer and an internationally recognized expert in the field of archaeoastronomy, undertook the task of examining Miller’s findings. For three decades, Krupp sought out every Southwest spot claimed to hold a depiction of the Crab supernova art, but failed to find the pivotal key drawings at White Mesa and Navaho Canyon. The surprise Krupp experienced was compounded by the fact that nobody seemed to know much about them at all, let alone where the artwork was supposed to be. In 2008, Krupp enlisted the help of two research associates from the Museum of Northern Arizona, Evelyn Billo, and Robert Mark. Billo and Mark were able to uncover documentation of the sites in the museum’s archives and subsequently, after obtaining tribal permits to search within the Navajo reservation, mounted an expedition to find the two key sites, the very basis of Miller’s hypothesis.

50

5. Supernovae

White Mesa was rediscovered, nestled in the sheltered cave hollowed out of a face of a tall eroded rock pinnacle. At first, Krupp found the impression quite distinctive, indeed, in keeping with Miller’s analysis. However, upon closer inspection, the painting of a crescent moon and a star looked somewhat brighter and fresher in appearance when compared to other pictographs on the wall, which time had clearly faded. Also, Krupp wasn’t convinced over the style of the painting, which did not seem to be in keeping with the date, almost appearing too modern. As Krupp examined the painting further, it led him to believe there were other explanations for what the artwork represented, one such interpretation being a spirit figure related to religious beliefs of the people of the Southwest. Krupp argued that the lines on the wall could just as easily represent a round head (the star), with a horn (the crescent) protruding from it, or even a scalping knife. Krupp’s understanding offered a very plausible alternative suggestion to Miller’s theory, and more so, Krupp’s findings were more consistent with the dating of the painting. Having left the Mesa artwork, the research team traveled in search of the second painting in the Navaho Canyon. Whereas the Mesa artwork did offer some difficulty in its finding, the second image presented a far more difficult task, with Krupp and his team struggling to discern the image, as it was embedded in a much larger design. Krupp concluded that the star and crescent were, in reality, simply part of a much bigger picture, with too many other patterns close at hand, along with depictions of animals and birdlife. Miller, he felt, had taken the star and crescent out of a wider concept, with his photograph framing just the star and the crescent, which were in fact integral parts of a much more elaborate piece of art. With Miller’s evidence open to interpretation on a seemingly wider scale after Krupp’s findings, the whole idea seemed on rocky ground. However, the Anasazi residents of the Chaco Canyon were also attentive to the movements of the heavens, with the famous Sun Dagger on Fajada Butte in the center of the Chaco Canyon, a solar calendar that heralds the winter solstice when a band of light floods the notch in the way of Casa Rinconada’s Great Kiva on the summer solstice, and with locations marked within the Great Kiva thought to create a simple stellar observatory. Similar phenomena can be seen throughout the Chaco Canyon and San Juan basin to the northwest. Many Chacoan buildings are thought to have been aligned to capture solar and lunar cycles and, in doing

Native American

51

so, would have relied upon great skill and knowledge of building in order to coordinate such structures. From the mid-800 s and over the next 300 years, the Chaco Canyon became a major center of culture for the ancient Pueblo peoples, a Native American culture that spanned the present-day Four Corners regions of the United States, comprised of southeastern Utah, northeastern Arizona, northwestern New Mexico, and southwestern Colorado. Despite the raw beauty of Chaco Canyon with its high-desert landscape, long winters, short growing seasons, and marginal rainfall, it was here that the Puebloan culture took root and flourished. The Chacoan culture and background can be traced back in part to the Oshara tradition, which developed from the Picosa culture. The Chacoans quarried sandstone blocks and hauled timber over great distances to assemble 15 major complexes, which, until the nineteenth century, remained the largest buildings in North America. However, it was the mid-800 s that saw the true scale of the architecture that was to establish the peoples and their culture. Using masonry techniques that were innovative for their time, massive stone buildings were erected (Great Houses), containing hundreds of rooms in their multi-storied buildings. Intensive planning went into their construction, whereby instead of simply adding extensions onto existing buildings, which would have sufficed, these structures were built from scratch, taking decades – in some cases, centuries – to complete. Not only were these houses often orientated to solar, lunar, and cardinal directions, lines of sight between the structures allowed for an intricate network of communication. The buildings also incorporated sophisticated astronomical markers and water control devices with the structures ultimately placed within a landscape surrounded by sacred ­mountains, mesas, and shrines that still have deep spiritual meaning for the descendants of the Chacoans. In the years to follow, these great houses were connected by a network of roads to other buildings throughout the region. The connected buildings, which totaled 150 throughout the San Juan Basin, served for the most part, when not in use, as examples of public architecture, used at times to bring the populace together for ceremonies. They would also be used to receive groups from outside the basin, where visitors to the canyon could trade with the residents at one specific location – perhaps not only trading wares, but gathering knowledge from other lands. So highly regarded were

52

5. Supernovae

these gatherings that it has been suggested that Chacoans even distributed food to surrounding clans and their growing population when the climate had failed them and their crops. It was near one these great houses, Penasco Blanco, where, on the underside of a shelf below West Mesa in Chaco Canyon, that artwork was discovered that would have dovetailed nicely into Miller’s theory of the possible recording of the supernova. For here lay a panel that contained three symbols: a large star, a crescent moon, and a handprint. A very similar ‘capture’ of an event in the night sky. Halley’s Comet made an appearance just a few years after the 1054 supernova, two events that would each have inspired the astronomical savvy Chacoan race to record them in the form of cave art. Positioned below the large star, crescent moon, and handprint is another set of drawings. These drawings show three concentric circles, approximately a foot in diameter, with huge red flames trailing to the right. Could the artwork be a depiction of the path of Halley’s Comet over a sequence of nights? Did the Chacoans set aside a certain section of the panel to record irregular happenings in the night sky, like the explosion of a star or the passing of a fiery comet? Every eight and a half years, the Moon and Earth return to approximately the same positions they were in on July 4, 1054. If you were in Penasco Blanco around such a time, positioned with a telescope under that very shelf of West Mesa looking at the sky, the heavens would provide a very interesting potential correlation. If you waited until the Moon was in a position pointed to by the fingers of the hand in the painting, then used the diagram under the shelf to position the telescope at the large star in the ­petrograph, upon peering through the telescope, you would see the Crab Nebula. Whatever you believe about the Chacoans, one prominent fact besides their interest in astronomy remains. The sum of the Chacoans’ total activities and response to change was significant and should not be underestimated when taking into account the fact that they imposed a great binding influence upon many different peoples across the region aside from their own. That in turn shows a great will to not only respect others and their chosen paths, be it in religious beliefs or types of commerce, but a collective understanding that in order to grow as a community they would need to embrace others, making the sum of the parts of the society greater than its combined total.

European and American

53

Inevitably, change came that the Chacoans had little control over, with the model of living that they had created slowly being eroded as construction of new buildings slowed, and the administrative and cultural center of the region that lay at the very heart of their ethos began to irretrievably shift. Many of the population simply migrated to new areas, realizing that there was much to see and accomplish beyond the canyon, a natural and progressive step if they were to evolve beyond what they had become, without letting themselves become an arrested culture.

European and American It wasn’t until much later that Europe started to take an interest in the Crab Nebula. In 1731, English astronomer John Bevis (1695– 1771) turned his telescope to the same patch of sky in Taurus. Bevis, also a doctor and an electrical researcher, is best known for discovering the Crab Nebula, and for the calculation of a prediction rule for the eclipses of Jupiter’s moon. Bevis is also credited with a compilation of a star catalog entitled Uranographia Britannica. In 1745, Bevis set about publishing his new star atlas, which would replace the work of John Flamsteed (1646–1719). Bevis acquired subscribers, had 52 copper plates for the star maps engraved, and even pulled a number of prints from each plate. Unfortunately, around 1750, his printer went bankrupt, the plates were sequestered by the court, and the intended Uranographia Britannica was never published. However, a number of pre-publication proof sets did survive. The Crab Nebula also has a history that incorporates that of Halley’s Comet. Charles Messier (1730–1817) found the nebula while searching for comets. As a keen comet hunter Messier, who noted the nebula wasn’t moving, thus concluding that it was not a comet, decided it would be extremely helpful to compile a catalog of such phenomena as the Crab Nebula in order that other comet hunters could rule out such phenomena in their own pursuit of finding comets. In 1757, in a re-examination of calculations taken by Sir Edmund Halley (1656–1742) by French mathematician and astronomer Alexis Clairaut (1713–1765), Clairaut was encouraged to make his own prediction about a possible return, citing 1758. Along with colleagues Jerome Lalande (1732–1807) and Nicole-­ Reine Lepaute (1723–1788), Clairaut researched the possible effect

54

5. Supernovae

of Jupiter and Saturn on the trajectory of Halley’s Comet, their findings concluding that the comet should reappear in the constellation of Taurus, which is where Messier decided to look before stumbling upon the nebula! It is interesting to note the participation of Lepaute in the work. Lalande had recommended her to Clairaut as a very capable person who would give great assistance to the calculations regarding the return of Halley’s Comet. The three had worked religiously on the project for 6  months solid, with the fruits of their labor predicting a return on April 13, 1759; the actual comet arrived just ahead of their estimates on March 13, 1759. Sadly, despite the considerable time and effort given to the research by Lapaute, Clairaut completely ignored her input, which in turn infuriated Lalande, who stated that Lepaute was the “most distinguished female astronomer ever.” Both Lalande and Lepaute would work together on many subsequent projects. Aside from her work on Halley’s Comet, Lepaute is credited with her work as part of Lalande’s team, which calculated the ephemeris of the transit of Venus and also with regards to calculating the exact time of a solar eclipse that occurred on April 1, 1764, and in the creating of a group of star catalogs. German-born British astronomer William Herschel (1738– 1822) made several observations of the Crab Nebula between the years 1783 and 1809, but it is not known whether or not he was aware of its existence in 1783, or if he discovered it independently of Messier and Bevis. What is apparent is that during the time Herschel observed the nebula he had concluded that it was a group of stars. Named after Herschel, the European Space Agency’s (ESA) Herschel Space Observatory (HSO), which was operational between 2009–2013, along with the Hubble Space Telescope (HST), studied the Crab Nebula using an array of instruments including the photoconductor array camera and spectrometer (PACS). Along with two other such instruments, PACS made observations of the Crab Nebula in the far infrared and sub-millimeter wavelength region. In 1913, American astronomer Vesto Melvin Slipher (1875– 1969) published his spectroscopy study of the sky, and the Crab Nebula was one of the first objects to be studied. Slipher spent his entire career working at the Lowell Observatory, becoming assistant director at the facility in 1915, acting director in 1916, then director from 1926 until his retirement in 1952. His elder brother Earl Charles Slipher (1883–1964), who also spent time at the Lowell Observatory, became a noted planetary astronomer,

European and American

55

concentrating on the planet Mars. Vesto used spectroscopy to investigate the rotation periods of planets and the composition of their atmospheres. He was also responsible for hiring American astronomer Clyde Tombaugh (1906–1997), actually supervising Tombaugh’s work ahead of his discovery of Pluto. In 1918, American astronomer Heber Doust Curtis (1872– 1942) classified the object as a planetary nebula, this classification holding true until 1933 when it was disproved. Curtis, who worked at the Lick Observatory from 1902 to 1920, continued the work started by fellow American astronomer James Edward Keeler (1857–1900) on surveying nebula. Curtis was the first to notice the polar jet associated with Messier 87, one of the most massive galaxies in the observable universe. In 1921, American astronomer Carl Otto Lampland (1873– 1951) observed changes in the nebula’s shape. These changes are not something Lampland could have observed for himself. Rather, he was comparing his observations to those taken across the past two centuries by other astronomers. Granted, many of the observations were hand-drawn, but what was apparent from the drawn pictures and accompanying photographs was that the nebula was expanding. A reoccurring theme among all the drawings is that the nebula bears no resemblance to a crustacean. The responsibility for the name lies with Anglo-Irish astronomer William Parsons, third Earl of Rosse (1800–1867), who observed the object in 1840 using a 36-inch telescope, his drawing taken to look something like a crab. Parsons had several instruments built, including a 72-inch telescope built in 1845. Colloquially known as the “Leviathan of Parsonstown” (Parsonstown is now in Offaly, Ireland), which at the time, was the largest telescope in the world until the construction of the 100-inch Hooker Telescope in California in 1917. The Hooker telescope remained the largest of its kind until 1949. Ironically, Parsons did turn the larger telescope to view the Crab Nebula, with his improved drawing creating a totally different picture from his earlier crab-like drawing made using the smaller telescope. However, the name had already stuck! During his career, Lampland was involved with projects at the Lowell Observatory in Flagstaff, Arizona (one of the oldest observatories in the United States), including observational work on Mars and the search for Planet X, which was sparked after the discovery of Neptune in 1846. At that time there was considerable speculation that another planet may exist beyond Neptune’s orbit.

56

5. Supernovae

Lampland, who was invited to work at the Lowell Observatory by Percival Lowell (1855–1916), is also credited with the discovery of an asteroid on March 24, 1931. Named 1604 Tombaugh, after Clyde Tombaugh, the asteroid is a rare type of Eoan asteroid from the outer region of the Asteroid Belt. A year previously, Tombaugh had supposedly discovered the elusive Planet X, namely Pluto! In the same year as Lampland had suggested changes to the size of the Crab Nebula, American astronomer John Charles Duncan (1882–1967) also demonstrated that he believed the remnant was indeed expanding. Duncan’s demonstration was a photographic one in which he made a comparison between a photograph taken with the 60-inch telescope at Mount Wilson Observatory in 1909 by George Willis Ritchey (1864–1945). Ritchey had become head of instrument construction at Mount Wilson, actually producing the telescope from which the photograph was taken. In his career, he was also chief optician at Yerkes Observatory, with work also undertaken for the Hooker telescope. By comparing the 1909 photograph with one Duncan was to take for himself from the same telescope in 1921, Duncan was able to demonstrate outward motions in the filaments of the Crab Nebula. He later confirmed these motions with another photograph taken in 1938, thus conclusively showing an expanding envelope such as has been observed around other novae. The year 1921 was also when Swedish astronomer Knut Lundmark (1889–1958) – professor of astronomy and head of the observatory at Lund University in the province of Scania, Sweden from 1929 to 1955 – first noted the proximity of the Crab Nebula to the historical supernova of 1054. Lundmark is also noted for his valuable contributions to the famous Shapley-Curtis debate of 1920 that, aside from the central point of the scale of the universe, also involved the question of whether nebulae were galaxies or concentrations of glowing gas. The Great Debate, as it was referred to, involved Heber Curtis, then of the Lick Observatory, and American scientist Harlow Shapley (1885–1972), of Mount Wilson Solar Observatory. Shapley argued that the universe was comprised of a single galaxy, while Curtis held that it contained many galaxies. In holding these positions, each came to different conclusions regarding the celestial objects astronomers at the time called “spiral nebulae,” the nature of which at the time was unclear. Curtis thought that the nebulae were galaxies external to our own, while Shapley argued that they were clusters made up mostly of gas. Although Curtis was correct, Shapley was correct, too, in arguing that our own galaxy the Milky

European and American

57

Way was larger than previously thought, and for showing that our Sun was not at the center of the galaxy. In a way, no clear winner emerged, but it did invoke a different level of understanding and thought, which has been instrumental in our understanding of the sheer scale of the universe. In 1928, American astronomer Edwin Hubble (1889–1953) also suggested the association between the Crab Nebula and the supernova of 1054, an idea that remained controversial until the nature of supernovae was more fully understood. As with Herschel and the Herschel Space Telescope, the Hubble Space Telescope (HST) has peered at the Crab Nebula, and also its counterpart, the Southern Crab Nebula, in the constellation of Centaurus. It wasn’t until American astronomer Nicholas Ulrich Mayall (1906–1993) was working on the newly built spectrograph at Lick Observatory that the necessary missing information was gathered to prove both Lundmark and Hubble correct. Mayall was the first to determine the radial velocities of many knots of gas in the Crab Nebula. Using a combination of this new data plus work conducted and previously published angular rates of expansion of the nebula, he became the first person to recognize and more importantly demonstrate that the Crab Nebula was the remnant of the SN 1054, rather than a classical nova. Mayall’s proof was to ignite a new era in itself, the age of searching for other historical supernovae, seven of which have been discovered by using the same methodology. However, as a landmark point in astronomical history, the Crab Nebula became the first object recognized as being connected. A report released in March 2007 by a team of astronomers recalculated the explosion date of the supernova and found agreement between their measurements and the classic date of a. d. 1054, the appearance of the “guest star” (a reference made by the Chinese to the sudden appearance of a star against the normally accepted backdrop), seen in the constellation of Taurus. The research team, led by Gwen C. Rudie, staff astronomer at the Observatories of Carnegie Institution for Science in Washington, D.  C., along with Professor of Physics and Astronomy Robert A. Fesen and Toru Yamada from Japan’s Subaru Observatory in Hawaii, used photographs taken 17 years apart to study the expansion speed of the Crab Nebula, the results of which confirmed the dating as accurate. The astronomers measured the proper motion of the supernova debris across the plane of the sky over a 17-year period. By detecting the outermost part of the supernova remnant, which manifests itself as a very faint “jet” of stellar debris, the

58

5. Supernovae

findings show clearly for the first time that the Crab exploded around the middle of the eleventh century, which corresponds with historical records. However, not all of the astronomers’ findings were so conclusive. Although the Crab Nebula’s location in the sky agreed with the reported position of this new bright star that had appeared, several studies of the expanding cloud of stellar debris did not conform to the expansion rate, unexpectedly indicating that the debris was expanding much too fast to be associated with the supernova explosion of 1054. The rates suggested a point in time much later, towards an explosion date that would have occurred in the twelfth century. In order to counter this anomaly, it has been proposed that the remnant’s central pulsar emitted such copious amounts of energy it actually accelerated the expanding cloud of debris, making it move faster with time. It is impossible to think that the surviving records from around the globe equate to all of the documentation resulting from direct observations of SN 1054. The records of many civilizations seem to have perished with the peoples themselves, but as time advances through the coming years, this does not necessarily mean that the portal back to finding the work closes even further – in fact, it opens even wider. With new advances in technology in the field of archaeology and archaeoastronomy, the possibilities of future findings from either present-day cultures or long-lost civilizations remain.

Other Records of Supernova RCW 86 The oldest recorded supernova is RCW 86, which Chinese astronomers saw in a. d. 185. Their records show this guest star staying in the sky for 8  months. The Chinese described the “new star” as resembling a “Bamboo mat.” “The Book of Later Han”  – or “History of the Former Han,” a history of China from a. d. 25 to a. d. 220  – described the associated colors, of which there were five, as “both pleasing and otherwise.” Until 2006, it had long been thought that the observation of RCW 86 (from the nebula catalog created by astronomers Rodgers, Campbell, and Whiteoak) was not of a supernova but of a distant,

Other Records of Supernova

59

slow-moving comet. The recorded observation was associated with a constellation called Nan Mun, which has led modern astronomers to believe that the event corresponds to the stellar remnant now known as SN 185, which sits between the constellations of Circinus and Centaurus in the direction of Alpha Centauri. It wasn’t until the 1960s that scientists actually determined that the cosmic object observed by the Chinese was a supernova. Infrared views taken by NASA’s Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE) reveal that the star explosion detonated inside a region of space that was relatively free of gas and dust. This allowed the debris to travel out much farther and faster than expected. According to astronomer Dr. Brian J. Williams, the remnant is two to three times bigger than one would expect for a supernova witnessed so long ago. RCW 86 is a Type Ia supernova, triggered by the relatively peaceful death of a star similar to our Sun. The star then followed the currently accepted pattern of shrinking into a white dwarf before collapsing and then outwardly exploding. The study, which combined the work of Spitzer, WISE, the Chandra X-Ray Observatory, and the European Space Agency’s XMMNewton Observatory, showed for the first time that a white dwarf can create a cavity-like empty region of space around itself before exploding in a Type Ia supernova event. This would explain why the remnants of RCW 86 are so substantial. When the ­explosion occurred, the cavity would have allowed the resulting ejected material to erupt out unimpeded by gas and dust. This would also have allowed the star’s remnants to be cast out rapidly. At a distance of approximately 8000 light years and measuring about 85 light years in diameter, the data gathered from both Spitzer and WISE were further examined. After measuring the temperature of the dust that makes up the RCW remnant, then calculating how much gas had to be present inside the supernova remnant to heat the dust to those temperatures, researchers discovered that the supernova remnant had existed in a low-density environment for much of itself, pointing to the presence of a cavity. RCW 86, which occupies a region of the sky in the southern constellation of Circinus that is slightly larger than the full Moon, may well have been recorded in Roman literature, although no records have been found of the event, with modern-day X-ray studies of the remnant seemingly giving a good parallel with regard to previous thoughts of dating the supernova.

60

5. Supernovae

SN 393 Chinese records also record a guest star in a. d. 393 in the modern constellation of Scorpius. The extract of text that mentions the appearance of the star also mentions that the sighting and documentation of what was probably a supernova were made during the second lunar month of the year 18 of the Ta-Yuan reign period, concluding that the guest star disappeared during the ninth lunar cycle. The second lunar month would correspond to the period of February 27 to March 28, 393, while the ninth lunar month ran from October 22 to November 19, 393. However, there is no mention of the brightness, stating that it only disappeared after 8 months. Until 1975, the Chinese record was considered to probably be that of a bright nova with a secondary maximum. However, as the event occurred in a particularly dusty part of the galactic plane, the appearance of the guest star for a period of 8  months seemed unlikely. Another record that exists thought to have a connection with SN 393 is that of Roman Latin poet Claudius Claudian (a. d. c.370­c.404), who describes a visually bright star in the heavens around 393 that could readily be seen even at midday. Although several researchers have suggested that this account may indeed be a ­reference to SN 393, Scorpius would not be visible near midday in March, when the Chinese first reported the guest star of 393. During 1996, ROSAT, the German Aerospace Center’s satellite X-Ray telescope (launched on June 1, 1990) discovered a nearby supernova remnant that, having discounted all the other possible sources in the area, was a good match for SN 393. Unconfirmed possible supernovae events may have been recorded in a. d. 369, 386, 437, 827, and 902. None of these has been associated with a supernova remnant and so they remain only candidates for being supernovae. Over a period of 2000 years, it is estimated that Chinese astronomers recorded a total of 20 such candidate events, including later explosions that were also noted by Islamic, European, and possibly Indian and other observers.

SN 1006 SN 1006 is remarkable in the fact that it is likely to have been the brightest observed stellar event in recorded history, with an estimated visual magnitude of −7.5, approximately 16  times as bright as Venus. Between April 30 and May 1, 1006, the supernova

Other Records of Supernova

61

occurred in a spectacular outburst. According to records, the event was witnessed by various civilizations across the globe – indeed, possibly on a par with the perhaps the more widely acknowledged SN 1054. At a distance of 7200 light years SN 1006, it was reported, was clearly visible during the daytime. Records of the outburst were recorded in China, Japan, Iraq, Egypt, Syria, and on the continent of Europe, in present-day France. As with SN 1054, there is also the possibility that it was recorded in North American petroglyphs. So powerful was the outburst that if the supernova were to be placed where our Sun lies, it would destroy everything around it with a reach that would stretch as far as Jupiter, although its total capabilities remain in question. Research, though, has suggested something that does provide food for thought with regard to supernovae and their capabilities. SN 1006 was a type Ia supernovae, the class of supernovae that can irradiate Earth with significant amounts of gamma-ray flux, compared to the typical flux from our Sun, up to distances on the order of one kiloparsec (one parsec equaling about 3.26 light years). Although SN 1006 did not appear to have such significant effects, a signal of its outburst can be found in nitrate deposits in Antarctic ice. The understanding behind the cause of the SN 1006 is of the type of supernova that occurs in binary systems, those consisting of two astronomical objects bound together by their gravitational pull. As the two white dwarfs associated with the system orbited each other, they lost energy in the form of gravitational waves and eventually collided, creating the epic blast. SN 1006’s associated supernova remnant for this event was not identified until 1965, when radio astronomers Douglas K. Milne and Dr. Francis Frederick Gardener used the Parkes Radio Telescope to demonstrate a connection to a known radio source, PKS 1459–41, located near the star Beta Lupi in the southern constellation of Lupus. At a distance of 383 light years, Beta Lupi is a giant star with an estimated age of around 25 million years. Milne and Gardner used Parkes to produce a contour map of emissions from the part of the sky where the “new star” had appeared in 1006. The map showed a shell-like structure, just as you would expect from an expanding cloud of debris in space. Persian scientist and philosopher Ibn Sina (a. d. 980–1037) noted a bright object appearing in the sky in 1006. A group of German researchers, which included astrophysicist Ralph Neuhauser, examined Ibn Sina’s texts, called Kitab al-Shifa, which include work in physics, meteorology, and other topics he was interested

62

5. Supernovae

in, including medicine and astronomy. The Kitab al-Shifa contains an observation of what is thought to be the supernova, but the account had been viewed as discussion of a comet. The section that makes the reference to the star has been the subject of previous studies to determine, and hopefully ultimately conclude, exactly what Ibn Sina had seen. In the time since Neuhauser and other researchers from different countries studied the account, it would seem that earlier presumptions that he was observing from Iran were incorrect, placing Ibn Sina as having been more likely to have observed the supernova from Uzbekistan, a crucial piece of information, which gives a clearer picture as to his own viewpoint of the night sky before and during the appearance of the supernova. Given the year references, it would appear most likely that he was observing the nova. In addition to the timing, which in itself is conclusive enough for many researchers, the translation seems to point to more of a sudden appearance, with Ibn Sina describing an object that threw out sparks, was very bright, and changing color before ultimately fading away. Furthermore, according to the translation, the new star started out as a faint greenish yellow, which twinkled widely at its peak brightness, changing to a more whitish color before fading away. Although perhaps not looked upon as being an overly scientific analysis, the references are quite the opposite in practice, as realizing how the supernova changed hue over time, as well as tracking its recorded brightness, helps modern astrophysicists better understand the classifications that have been allocated to supernova. In addition to the texts of Ibn Sina, Neuhauser found another piece of evidence for SN 1006 in works by a historian named al-­ Yamani from the Yemen. Some of the texts refer to observers witnessing the guest star’s arrival even earlier than previously thought, which would affect modern understanding of the supernova’s evolution. Translation of the texts by al-Yamani would put the date of the sighting at April 17 plus or minus a few days, but this would point to the new star having been seen several weeks earlier, before its previously assumed earliest observation. The texts also state the supernova rising about half an hour after sunset. Given the star’s position in the sky, there are only a few dates on which that could have happened, and they fall in the middle part of April, which would correspond with the statement of a date in the texts. Also, al-Yamani’s records mark when the supernova rose in the sky relative to the Moon, and that, too, corresponds with dates between April 15 and April 18, based on the known positions of the Moon at the time.

Other Records of Supernova

63

According to Neuhauser, records from China, Japan, and Switzerland can all be interpreted in ways that back up the earlier date. Professor of physics and astronomy Bradley Elliot Schaefer, who has studied the timings of historical supernovae, agrees that ancient observations can be useful for working out when this supernova reached peak brightness, but remains unconvinced with regard to the color data mentioned by Ibn Sina. One issue is that the supernova was too close to the horizon so that the colors he reported might simply be effects caused by Earth’s atmosphere. In his findings, Schaefer is also quick to caution anyone who attempts to weave together various records of the event from different sources in their corresponding countries, stating that on each occasion any researcher will have to account for variations in brightness from observer to observer, with references making brightness parallels to Mars, Venus, and a quarter Moon, all of which greatly vary in brightness. Physician, astrologer, and astronomer Ali Ibn Ridwan (988– 1061) wrote of the supernova in a commentary on Ptolemy’s work Tetrabiblos (“Four Books”), which was a text on the philosophy and practice of astrology. Tetrabiblos was the companion book to Ptolemy’s text on astronomy, Almagest. Tetrabiblos carries equal weight with regard to astrology, its text concerning the study of astronomical cycles on earthly matters. Almagest remained a prominent work in astronomy until it was superseded by the acceptance of a heliocentric model of the Solar System, but Tetrabiblos remains an important theoretical work for astrology. In Tetrabiblos, the supernova is referenced as a large circular body, some three times as large as Venus, with the sky shining because of its light. As with other observers who had referenced the event, Ali Ibn Ridwan noted that the new star was low on the southern horizon. Some astrologers noted the event as a portent of plague and famine. The Chinese recorded the event, as they did the later SN 1054 event in Song Shi, alluding in sections 56 and 461 of the work to a star seen on May 1, 1006, in the constellation Di, east of Lupus and one-degree west of Centaurus – “Di” referencing a Chinese Root mansion. The Root mansion is one of 28 mansions of the Chinese constellations. The European constellation equivalent is Libra, with the Chinese constellation or “asterism” meaning the Azure Dragon’s chest and front foot. The Dragon is frequently referred to in the media feng shui, or fengshui (“wind-water”), also known as Chinese geomancy, a pseudoscience originating in China, which claims to use energy forces to harmonize individuals with their environment.

64

5. Supernovae

By December 1006, the bright star was again sighted in the constellation Di, with astronomer and astrologer Zhou Keming interpreting it to the emperor as an auspicious star, yellow in color and brilliant in its brightness, which would bring great prosperity to the state over which it appeared. This was at odds with most astrologers, who interpreted the event as an omen of warfare and famine. The reference to the star being “yellow” may well have been for political purposes, to possibly curry favor. As with SN 1054, much speculation surrounds the actual sighting by a society known as the Hohokam, located in the present states of Arizona, Sonora, and Mexico. There seems to be agreement between archaeologists that the Hohokam existed between a. d. 300 and 1500. The word Hohokam is borrowed from the O’odham or Pagago-Pima language of the Akimel O’odham, “River People,” formerly known as Pima, a group of Native Americans living in an area consisting of what is now central and southern Arizona. Hohokam is used by archaeologists to identify the group of people who lived in the Sonoran Desert, which covers parts of the southwestern United States in Arizona and California, and of northwestern Mexico in Sonora, Baja, California, and Baja California Sur. The desert, which measures 240,000  sq. km and is the hottest in Mexico, is home to the cultures of over 17 contemporary Native American tribes, with settlements at American Indian reservations in California and Arizona, as well as populations in Mexico. Other archaeologists refer to ancient Arizona as part of the Oasisamerica tradition, and instead call the Hohokam Oasisamericans. Oasisamerica is a term used by some, mainly Mexican, anthropologists for the broad cultural area defining preColumbian southwestern North America. The White Tank Mountain Regional Park in west-central Maricopa County, Arizona, encompasses a large swathe of desert and mountain environment, doubling as a nature reserve with mule deer and coyotes. These mountains are home to a number of archaeological sites, 11 in total identified within the park boundaries, seven of which include Hohokam villages. Although the remnants of the villages are not well preserved, what is in evidence is the apparently large number of petroglyphs that are liberally scattered throughout the park. Most are of Hohokam origin, but some were created nearly 10,000 years ago by Meso-Indians. Here, a petroglyph has been interpreted as the first known North American representation of a supernova, SN 1006. Much debate

Other Records of Supernova

65

surrounds the find and its validity. Could it be, though, that the people who lived here made such an observation, and impressed by what they saw, carved the image on to a rock? The most northerly sighting recorded of SN 1006 is in records kept at the Abbey of Saint Gall in St. Gallen, a town in Switzerland. The abbey, a UNESCO World Heritage Site, contains a renowned library with books dating back to the ninth century. The monastery itself was founded by a monk and priest named Saint Othmar (c.689 – c.759) in c.720. The annals include independent data on the magnitude and direction of SN 1006 when it was sighted from the abbey, with references to the new star remaining bright for 3 months.

SN 1181 SN 1181 also has a number of recorded sightings, the core of which herald from South China, North China, and Japan, by astronomers who observed a guest star between August 4 and 6, 1181. Eight separate texts document the supernova in the constellation of Cassiopeia, with observations recording the supernova being visible in the night sky for about 185 days. No account of the guest star appears to be preserved in European (or Arab) history. In the texts, the Chinese and Japanese systematically identify the object as a guest star, describing it as “large.” Although no exact positional measurements are extant, its location is described in relation to five separate star groups in the region of Cassiopeia. However, SN 1181 remains something of a puzzle. Radio astronomer Roland Josef Kothes has expressed concerns over the length of the explosion being too long for that of a nova. Kothes, whose areas of interest include interstellar magnetic fields, supernova remnants, and star formation, called into question the brightness of the guest star. Even at its peak brightness the star was much fainter than the four other bright supernovae of the second millennium, which outshone every star at night. SN 1181 merely matched Vega, the fifth-brightest star in the night sky, and after 6 months, it simply vanished. Professor and historian at the University of Durham F. Richard Stephenson (born 1941) was the first to provide the probable link between SN 1181 and a pulsar and supernova remnant in the region. Radio surveys of the area in more recent years have also linked the pulsar contained within the remnant, named 3C58, with SN 1181. The pulsar, which is a proposed quark star, a hypo-

66

5. Supernovae

thetical type of compact exotic star, lies at a distance of 10,000 light years (earlier estimates placed it at 27,000 light-years from Earth), with a rotation period of about 11 times per second. The optical component of 3C 58 was discovered in 1977 by Canadian astronomer Sidney van den Bergh (born 1929), on long exposure plates from the 5-m reflector at Mt. Palomar. Radio surveys have also been quite contradictive about the possible link between SN 1181 and 3C 58 being the associated remnant, the findings tending to favor the view that 3C 58 is considerably older, which would mean that the two are separate entities. Professor of physics and observational astronomer Robert Fesen, who specializes in supernovae and supernovae remnants, concurs with the notion of relative age, citing that 3C 58 is not linked with SN 1181, the problem being that 3C 58 is expanding slowly, which suggests it has been doing so for a long time. Therefore, a link to SN 1181 means 3C 58 is younger than the Crab Nebula, which we know and have accurately dated in line with SN 1054, even though it is larger than the Crab Nebula and is expanding at half the Crab’s speed. Kothes argues that 3C 58’s expansion has likely slowed in recent centuries. Kothes, astronomer at the Dominion Radio Astrophysical Observatory in Canada, undertook the work of measuring again the distance of 3C 58 from Earth, finding that the nebula is even less distant than the proposed 10,000 light years, at just 6500 light years from Earth. In that case, it would reaffirm the link to the supernova. This is so because the measurement made by Kothes changes the properties astronomers deduce for the nebula. Because the pulsar is closer, it followed that it must produce less synchrotron radiation – which electrons emit as they spin around magnetic field lines – than previously thought. The ultimate source for this radiation is the nebula’s pulsar. Astronomers use the pulsar’s age and spin to calculate how much energy it has injected into the nebula. If one of the former distances were correct, the minimum energy required for the synchrotron nebula to be produced is higher than the energy levels released since the birth of the pulsar. However, the recalculated distance of 6500 light years means the nebula is emitting no more energy than the pulsar can produce, convincing Kothes that 3C 58 marks the site of the SN 1181 blast. In turn, this would mean the blast emitted by SN 1181 was even weaker than astronomers previously thought. At the proposed distance of 6500 light years, the explosion was roughly a

Other Records of Supernova

67

fifth as luminous as the 1987 supernova, which appeared in the Large Magellanic Cloud. SN 1987A was a peculiar supernova that, at a distance of 168,000 light years from Earth, was the closest observed supernova since the supernova of 1604, named after German astronomer Johannes Kepler (1571–1630). Indeed, the closest observed since the invention of the telescope. SN 1987A was a Type II supernova caused by the collapse of Sanduleak-69,202, a star located on the outskirts of the Tarantula Nebula. The star, named after Romanian-American astronomer Nicholas Sanduleak (1933–1990), was originally charted by Sanduleak in 1970, but remained just a number in a catalog until identified as the star that exploded.

SN 1572 SN 1572, or B Cassiopeia, was a Type Ia supernova that appeared early in November 1572. It was also named Tycho’s supernova after Danish astronomer Tycho Brahe first observed the “new star” in the heavens on November 11, with the object visible to the naked eye until March 1574. The supernova attained an apparent magnitude matching that of Venus, about −4, and could easily be seen by day. Sighted in the constellation of Cassiopeia, SN 1572, Brahe had observed the new arrival while gazing up at the night sky while walking home, noting that there was a star that he did not recognize near to the zenith. Despite being referred to as Tycho’s supernova, it is claimed that he was not the first to have observed it. There are claims that it was sighted in August, several months before Brahe’s sighting, with German astronomer Wolfgang Schuler claiming that he observed the “new star” on November 6. The star was seen throughout Europe and Asia by many observers, but the credit remained with the Dutch nobleman and neophyte astronomer, who upon sighting the star was so inspired that he dedicated the remainder of his life to charting the positions of the stars and planets. Ironically, just prior to the discovery, Brahe had invented a sextant that allowed him to measure the distances between stars, locate the exact position of the “new star,” and measure its angular distance from other stars in Cassiopeia. His enthusiasm led him to write a book, De nova et nullius aevi memoria prius visa stella (“Concerning the Star, new and never seen in the life or memory of anyone”), which made him somewhat famous. Published in 1573, reprints were overseen by Johannes Kepler in 1602 and 1610.

68

5. Supernovae

The work, which contained Brahe’s own observations and the analysis of and contributions to the sighting of the “new star” was instrumental in the supernova gaining his surname in its title, with Schuler’s claim seemingly overlooked and unfortunately relegated to that of just another observer. However, Schuler was not alone. Almost as accurate as Brahe in his work was English mathematician and astronomer Thomas Digges (1546–1595), one of the first to expound the Copernican system in English. Digges went considerably further than Copernicus, proposing that the universe is finite, containing infinitely many stars, and some consider his proposition to be the first of its kind. Digges, who was also considered the first to postulate the “dark night sky paradox” (the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe), attempted to determine the parallax of SN 1572, concluding that it had to be beyond the orbit of the Moon. Interestingly, the widow of Digges, Anne St. Leger (1555–1636), later married Thomas Russell, an executor of William Shakespeare’s (1564–1616) will! English/Welsh mathematician and astronomer Dr. John Dee (1527–1608) was also an observer credited with making observations of SN 1572 on a par with those of Brahe. However, it is considered that Dee and his compatriots, while certainly not naïve, lacked the instruments and proof. Indeed, Thomas Digges was entrusted to the guardianship of Dee after the death of his father, well-known mathematician and surveyor Leonard Digges (c.1515-­c. 1559). Thomas Digges published a new edition of his father’s perpetual almanac, A Prognostication everlasting (considered a best-­seller in its time), to which he added new material, the most important of which was A Perfit Description of the Caelestiall Orbes according to the most aunciente doctrine of the Pythagoreans, latelye revived by Copernicus and by Geometricall Demonstrations approved. Contrary to the Ptolemaic cosmology of the original book by his father, the additional material featured a detailed analysis of the Copernican model of the universe, something not as well-read and generally poorly known. Interestingly, there are claims that Leonard Diggs independently invented the reflecting telescope, and/or possibly the refractor. It was thought to have been invented to assist his surveying work that involved experiments with mirrors and lenses in which both he and Thomas Digges were involved. Although seemingly difficult to prove, a possibility exists that somewhere

Other Records of Supernova

69

between 1540 and 1559, a functioning telescope of either a reflector or refractor construction was built. There are references to such work in some of the text published by Thomas Diggs, but doubt remains, as Thomas was known to have adored his father, perhaps exaggerating some of the claims. However, contrary to this, some of the text refers to the use of proportional glass to view objects at a distance! English mathematician and astrologer Thomas Allen (1542– 1632) was instructed by Queen Elizabeth I (1533–1603) to explain and give advice upon the ‘new star’ that had appeared in C ­ assiopeia. His most learned response is remembered in text written by English biographer and philosopher John Aubrey (1626–1697). The appearance of the “new star” caused a considerable issue in China, its appearance happening during the era of the Ming dynasty. A dispute arose between reformer and statesman Zhang Juzheng (1525–1582), who served as Grand Secretary in the late Ming dynasty, and the young Wanli Emperor (1563–1620). In accordance with cosmological tradition, the emperor was warned about misbehaving since the “new star” was interpreted as an evil omen. Many old Chinese history books on the Ming dynasty commonly assert that Wanli’s regime caused the rapid downfall of the dynasty, although countering this are reports that his behavior and generally neglectful approach was a result of severe depression brought on by the death of Zhang Juzheng, who had been appointed dedicated advisor to Wanli at the age of just ten, as instructed upon the death of his father, Zhu Zaiji, 12 Emperor of the Ming dynasty. Other notable sightings of SN 1572 were made by Sicilian mathematician and astronomer Francesco Maurolico, Spanish scientist Jeronimo Munoz, Czech naturalist Tadeas Hajek, and scientist Bartholomaus Reisacher. Hajku published his own work on the supernova and was in frequent contact with Brahe. For two weeks, SN 1572 was the brightest star in the sky, outshining all rival bright stars with records, noting a change in color by the end of November 1572, shifting from bright white to yellow. The colors continued to change over time from yellow to orange and lastly a reddish tint, until it finally disappeared. The sighting and timings associated with its appearance and disappearance, color changes and general fascination attracted much attention in many countries, thankfully not just as a spectacle to observe but a happening that made SN 1572 one of the most important observational events in the history of astronomy. The most reliable contemporary reports of the time state that the “new star” itself burst

70

5. Supernovae

forth soon after November 2, and by November 11 it was already brighter than Jupiter. Around November 16, it reached its peak brightness, giving it equal and in some cases greater brightness than Venus. There is a remnant associated with the SN 1572, and although it has been observed optically, it was first detected at radio wavelengths, often being referred to as Tycho’s supernova remnant or 3C 10. An X-ray spectrum of the remnant showed that it was almost certainly of Type Ia, but that was not beyond doubt. However, that doubt was finally resolved in 2008, when the detection of a light echo (in which light reflects off surfaces distant from the source, similar to sound echo but given the speed of light much faster) gave confirmation of its Ia status. The distance of the remnant is calculated at between 6500 and 16,300 light years, although more recent studies suggest figures more in line with 8000–10,000 light years. The search for the supernova remnant was fruitless until 1952, when two astronomers working at Jodrell Bank Observatory, Lower Withington, England, reported a detection by radio. Radio astronomers Robert Hanbury Brown (1916–2002) and Cyril Hazard had their findings confirmed in 1957 by astronomers at the Cambridge Radio Telescope. Because the radio remnant was found and reported before the optical supernova-wisps were discovered, the designation 3C 10 is used by some astronomers to signify the remnant at all wavelengths, as it is also referred to by several differing titles. It wasn’t until the 1960s that the supernova remnant referred to as B Cas was discovered. Astronomers working at the Palomar Mountain Telescope in San Diego detected a faint nebula, much later being photographed by the ROSAT spacecraft. The remnant was observed with the Westerbork Synthesis Radio Telescope (WSRT) in 1971 and 1979. The telescope is based north of the village of Westerbork, Midden-Drenthe, in the northeastern Netherlands, consisting of a linear array of 14 antennas with a diameter of 25  m arranged on a 2.7-km east-west line, a similar arrangement to the One Mile and Ryle Telescopes at the Mullard Radio Astronomy Observatory (MRAO) in Cambridge, England, and the Australia Telescope Compact Array (ATCA) in Narrabri, New South Wales. The measurements taken by WSRT have been used to determine the radial expansion rate. Although there seems to be a higher rate found using radio data when compared to optical data, the general consensus points fall well within error range. The apparent discrepancy between radio and optical

Other Records of Supernova

71

data is primarily the low expansion speed at the position of the most prominent nebulosity, probably attributable to the deceleration caused by the higher density of material. The appearance of SN 1572 was instrumental in the revision of ancient models of the heavens and proved to be one of the many catalysts throughout astronomical history that ultimately engineered a change of thought and approach to the universe in which we live. It inspired the premise to produce better defined star catalogs and also recognition of the need to invent and manufacture better instruments with which to observe the night sky. Ultimately, as with SN 1604, SN 1572 was to prove a significant challenge to the long-held doctrine of the unchanging realm of the stars, as stated in Aristotelian dogma. It was a challenge whereby both its critics and those who defended the idea would have to acknowledge that the concept was flawed, but not so much that the architects of its design should feel belittled by their beliefs. The science and facts irrefutably paved the way to first an acknowledgement that a perception was wrong and then to embracing that which could not be challenged.

SN 1604 SN 1604, or the Kepler supernova, of which only the supernova remnants remain, took place in Ophiuchus, from the Greek “serpent-­bearer,” a constellation straddling the celestial equator. At a distance of 16,300 light years from the Sun, the supernova arose from the explosion of a white dwarf in a binary system and is one of the most recent Type Ia explosions known in our galaxy. SN 1604 is one of the few supernovae known to have occurred in the Milky Way (Fig. 5.2). Records of the sighting exist in European, Chinese, Korean, and Arabic records. At its peak, SN 1604 was brighter than any other star in the night sky, with an apparent magnitude of −2.5. It was the second supernova to be observed in a generation after SN 1572, seen by Tycho Brahe. Jan Brunovsky, Johannes Kepler’s assistant, first observed the phenomenon in October 1604, with Kepler himself studying the supernova in the early part of 1606, when the object had faded away from view with the naked eye. At its greatest apparent magnitude, the exploding star was brighter than Jupiter. No stellar remnant is known to exist, though traces of nebulosity are observable at the position of the supernova.

72

5. Supernovae

Fig. 5.2.  SN 1604. Kepler supernova remnant. (Courtesy of NASA.)

Records show that on the night of October 9, 1604, Europe turned to the southwestern sky, where Jupiter, Saturn, and Mars were slated to assemble in Sagittarius. Some believed it would herald a radical transformation of the world. As astronomers, astrologers, and other observers alike were watching the conjunction, it meant that there were a good number of sky-watchers looking in that very direction when the event occurred. The appearance of the supernova – precisely at the moment and in the place of the great conjunction marking the emergence of a fiery trigon – was held by German physician and astrologer Helisaeus Roselin (1545– 1616) to confirm his previous prognostication of a “universal transformation” of the world. Roselin (one of five observers who concluded that the Great Comet of 1577 was located beyond the Moon) had known Kepler since their student days and remained one of Kepler’s correspondents. Because of his leanings, though, Roselin placed more emphasis on astrological predictions associated with events than Kepler did, and though Roselin had great respect for Kepler as a mathematician, he rejected some of Kepler’s

Other Records of Supernova

73

cosmological principles, including Copernican theory. Roselin’s 1597 book De Opera Dei Creatonis is regarded as one of the major works of the late sixteenth century controversy over the formulation of a geoheliocentric world system. Also, following the appearance of a new star in 1572, SN 1572, he predicted that the world would end in 1654. Both Kepler and Roselin wrote reports in German with regard to the supernova event, and after the publication of works that followed, the pair entered into discussion, with each keen to promote their understanding of the universe, which heralded from such different methodological and theoretical standpoints. Kepler wrote of the star that it either signified nothing whatsoever for humankind or signified an important event that was beyond the grasp and understanding of any human. The pair kept up their arguments not just in larger publications but through a series of pamphlets written as dialogs, with Kepler openly criticizing Roselin’s predictions regarding the comet of 1604 in his book De Stella Nova in Pede Serpentarii (“On the New Star in the Foot of the Serpent Handler”), written between 1605 and 1606 and published in Prague. In this work, aside from the more important observational work carried out by Kepler on SN 1054, Kepler condemned Roselin concerning the supernova, arguing that in Roselin’s prognostications he had only picked out two comets, the Great Comet of 1556 and 1580. Roselin replied in 1609 that this was indeed what he had done, appearing to sweep the comment aside. When Kepler replied later the same year, he simply observed that by including a broader range of data, Roselin could have made a better argument. However, the arena for debate wasn’t solely owned by Kepler and Roselin. In 1606, Italian scholar Lodovico delle Colombe (c.1565-c.1623), published the work Discourse of delle Colombe, which he dedicated to Alessandro Marzi Medici, the Archbishop of Florence (1557–1630). In it, he showed that the guest star that had appeared in October 1604 was neither a comet nor a new star, defending an Aristotelian view of cosmology. The sentiment of the argument was supported by Johannes van Heeck (1579-c.1620), who held the generally accepted view of an Aristotelian model for the universe, or indeed similarly the Ptolemaic system. In this model the stars were fixed in their positions and unchanging, and if an unusual event took place among the stars, this suggested that they were not fixed in the “firmament” (a structure above the atmosphere of Earth, taking on the appearance of a vast solid

74

5. Supernovae

dome). The thoughts presented by delle Colombe met with a sharp response from Galileo Galilei. Just as Kepler and Roselin argued, delle Colombe and Galileo did so, too. However, delle Colombe defended his position that the new star was permanent rather than fixed, suggesting reasons for why it had not previously been observed. To support his argument, delle Colombe drew not only on astronomical observations but on the authority of Aristotle and others, including such acclaimed thinkers from the Conimbricenses (Jesuits who took over the intellectual leadership of the Roman Catholic world), Italian diplomat and cardinal Gasparo Contarini (1483–1542), and Italian scholar and physician Giulio Cesare della Scala (1484–1558), both of whom defended Aristotelianism against new thinking. Although cautious in his approach, Galileo wrote a response to dele Colombe’s ideas in Considerations of Alimberto Mauri on Some Passages in the Discourse of Lodovico delle Colombe (Alimberto Mauri being Galileo’s pseudonym). Although it was clear to delle Colombe that Galileo had written it, it did not detract from totally ridiculing his work even to the point of Galileo belittling him by calling him “nostro colombo” (“our pigeon”). It dispensed with the Aristotelian philosophy, demanding that the argument over the new star should be based on scientific fact drawn from observation and mathematics. In response in 1608, delle Colombe directly responded to “Alimberto Mauri” by publishing Risposte placevoli e curiose (Pleasant and Curious replies). In the work, delle Colombe attacked not only the ideas of Copernicus but linked the ideas directly to Galileo. Galileo is remembered for many contributions to science and astronomy, but some consider his arguments to at times to have been pursued perhaps a little too doggedly. Known for taking on the Catholic Church by championing the idea that Earth moves around the Sun, he seemed at times to go out of his way to argue, even engaging with a philosopher as to why ice floats on water. Although his primary arguments were correct, his belittling of legitimate evidence offered by those he engaged with did little for his reputation. His adversary with regard to this particular spat was once again delle Colombe. Indeed, so famous were some of the exchanges between the two that on this particular occasion, dozens of wealthy spectators gathered in Florence to watch the affair. Galileo’s explanation as to why ice floats on water was closer to the truth, but he went too far, condemning the reasons put forward by delle Colombe.

Other Records of Supernova

75

Galileo, whose self-confidence and ego carried forth his ideas, was also not immune to making statements that even when challenged, as he had challenged delle Colombe, he would vehemently defend. Nevertheless, for a man of his stature, defending arguments he had made, for example, that comets were optical illusions, seems like pure rage and defiance, rather than being open to analytical debate. In the De Stella Nova in Pede Serpentarii, Kepler states that SN 1604 was observable for almost a year, from October 1604 to October 1605. Kepler also mentions that observing conditions were good, particularly when it first became visible. With so many focused on that part of the night sky because of the conjunction, many eyewitnesses saw the new star appear, but among all those who saw the supernova, Kepler’s observations were particularly meticulous. The care Kepler took not only to record his own observations but to compile the observations of others makes De Stella Nova in Pede Serpentarii a very important record of both the supernova itself and the level of astronomy and understanding of the universe from the early seventeenth century. As soon as the star appeared that night in Ophiuchus, Kepler set to work recording every possible detail, all of which were seen with the naked eye. Kepler measured the angular distance from known stars, establishing that SN 1604 showed no noticeable movement. Kepler’s work also refers to the measurements made by German pastor David Fabricius (1564–1617), observing from Osteel, Lower Saxony, Germany, which paralleled his own work. Fabricius is remembered himself for making two major discoveries, the first being the discovery of the first known periodic variable star, Mira, in August 1596. Initially, Fabricius believed it to be “just” another nova, as the whole concept of a recurring variable did not exist at that time. When observing Mira and observing it brighten again in 1609, it became clear to him that a new kind of object had been discovered. Mira, in the constellation of Cetus, consists of a red giant star (Mira A) and a white dwarf companion (Mira B). Estimated to be between 200 and 400 light years distant from our Sun, the red giant is thought to be of the order of 6 billion years old. However, while the credit remains with Fabricius over the discovery of Mira being a variable star, there is a debate about whether or not it was discovered before him, perhaps as evidenced by a Greek astronomer Hipparchus’ Commentary on Aratus (a commentary on the popular poem written by Greek didactic poet Aratus). It has been proposed that certain lines in the text may well be about Mira. Evidence that the variability of Mira was known to

76

5. Supernovae

the Chinese, the Babylonians, and the Greeks is, at best, merely circumstantial. The second of the discoveries attributable to Fabricius, this time along with his eldest son, Johannes Fabricius (1587–1615), is the noting of the existence of sunspots, the first confirmed instance of their observation. Again, though, a challenge exists to this, but once more only in circumstantial reference, with statements in East Asian annals suggesting that Chinese astronomers may have discovered them with the naked eye before the telescopic observations of Fabricius and his son (his son having brought telescopes back from his university in the Netherlands). Kepler’s observations of SN 1064 allowed him to be certain that the “new star” showed no parallax, using known star positions in the constellations of Sagittarius, Ophiuchus, Aquila, and Scorpio. Kepler’s text also refers to his measuring of the brightness of the new star, which compared it to that of Jupiter, Venus, Mars, and that of several nearby stars. The low declination of the supernova over the latitude from which Kepler was observing in Prague likely caused atmospheric refraction, the deviation of light from a straight line as the light passes through the atmosphere, due to the variations in air density as a function of height. The deviation, which can cause such distortion as raising or lowering an image, or even stretching it or shortening it, would explain most of the errors that Kepler had recorded in his observations, although in the text, Kepler gives no indication of the times or atmospheric conditions at the time of making associated notes. However, so precise were the measurements and data collected by both Kepler and Fabricius that it allowed later astronomers such as Walter Baade to locate the supernova remnant.

SN 1885A Prior to 1885, the few supernovae that had been observed were relatively all local affairs, but this event marked the first supernova to have been witnessed that was outside of the Milky Way. Also known as “Supernova 1885,” the significance of the sighting was not fully appreciated until much later. Credit for its discovery falls upon several people, including Irish amateur astronomer Isaac Ward (1834–1916) who, while observing from Belfast, Northern Ireland, reported seeing a bright reddish object in the sky on the night of August 19, 1885. Ward observed that the object was near to the nucleus of M31,

Other Records of Supernova

77

shining at an estimated −7. Ward, who had detected the supernova with his one and only instrument, a 10.9-cm refractor, would seem by his actions to have in some way established a notable point in history, championing the amateur status that would be held for the discoveries of further astronomical phenomena, making the science not solely exclusive to professionals However, Ward did not immediately publish what he witnessed. He was not the first person to make the error of not publishing his findings immediately, but it was perhaps a lapse that cost him outright recognition for the find. Two days previously, French astronomer Professor Ludovic Gully appears to have been the first to see the supernova, while watching the heavens at a public stargazing event in Rouen. However, at the time, Gully dismissed what he had seen as either a telescope defect or that he was merely observing the effects of scattered moonlight. Gully also did not publish what he had seen. For both men, in particular Ward, not publishing the findings was to prove a mistake that they could not amend. On the night following Ward’s observation and 3  days after Gully made his, unknown to both, German astronomer Carl Ernst Albrecht Hartwig (1851–1923) had sighted the same object at Dorpat (Tartu) Observatory in Estonia, communicating his find on August 31, 1885. Hartwig had taken the time in between making the discovery and sending the telegram to make absolutely sure that the feature was not caused by reflected moonlight, waiting to observe again under more ideal circumstances – ironically, one of the reasons Gully had dismissed the object. Upon hearing the news of the discovery made by Hartwig, both Ward and Gully published their findings. In studies that followed, doubt has been cast over what Ward really observed, with questions over his estimated magnitude, which is significantly off from the later reconstructed light curve. Studies of the claims of all three – Ward, Gully, and Hartwig – found that credit for the find should be awarded to Hartwig. As a twist of irony for all three, the first reports of the discovery appeared before Hartwig’s discovery letter, which followed his telegram, since the letter was originally lost by Astronomische Nachrichten (one of the first international journals in the field of astronomy, founded in 1821), and only reprinted in a later issue. SN 1885A, also known as (S Andromedae), hailed from the M31 Andromeda Galaxy 2.5  million light years away. As with all these earlier supernovae, accurate classification would come much later. Within a few months of appearing, SN 1885A began to

78

5. Supernovae

fade from view, with its remnants discovered over a century later, in 1989. Its peak magnitude reached 5.85 on August 21, 1885, but after 6 months it had faded dramatically to +14. The supernova was reported as reddish in color, with its brightness declining rapidly. The detection of the supernova remnant was not made until 1988, when Robert Fesen, using the 4-m Mayall Telescope at Kitt Peak Observatory, discovered an iron-rich remnant explosion. With the discovery further analyzed by the Hubble Space Telescope in 1999, it was concluded that in this instance, given the spherical symmetry of the explosion, the supernova was not caused by components merging. There has been much debate about exactly what category SN 1885 A falls into. It remains the only Andromeda Galaxy supernova to have been visible from Earth.

SN 2003 fg Discovered in 2003 with the Canada-France-Hawaii Telescope (CFHT), located near the summit of Mauna Kea on Hawaii, and the Keck Telescope, also sited on Mauna Kea, SN 2003fg presented itself as a quite unusual supernova. It occurred in a galaxy some four billion light-years from Earth. The discovery was made possible through images taken by the research team working at the two telescopes, led by astronomer Professor Richard Salisbury Ellis (born 1950). The unusual aspect of the supernova was that as a Type 1a supernova it didn’t quite follow the expected parameters to actually “go nova.” It should not have been possible. The white dwarf in the binary system appears to have swelled to two solar masses before exploding, completely re-writing decades’ worth of astrophysical work that had been based around the Chandrasekhar limit. The supernova’s more formal title is SNLS-03D4bb, but it became more widely known as the “Champagne Supernova,” a nickname related to an outburst by Professor David Branch of the University of Oklahoma. Branch dubbed the supernova with the “champagne” tag after commenting that explosions that offer new insights into the inner workings of supernovae are rare, and this particular supernova gave cause for a celebration. SN 2003fg also gained the alternative names of “rouge supernova” and “super-Chandrasekhar supernova,” as it exceeded the expected mass stated by the Chandrasekhar limit as 1.4 solar masses, at which point the supernova is triggered. The progenitor of SN 2003fg went far beyond that limit, posing the question as

Other Records of Supernova

79

to why this was the case. Indeed, why did the supernova hold off exploding until well past the 1.4 solar mass limit? One such explanation is that the explosion was the result of the merger of two white dwarfs, yielding the combined mass level before detonation. Another explanation leans towards the theory that the white dwarf was spinning so fast that centrifugal force thrust some mass away from the center and kept the whole thing from collapsing until it hit 2 solar masses. With new supernova events, coupled with every new technique that has been involved in researching historical supernova, the combined effort of both telescope and ancient written text remains an integral part of the ongoing development and understanding of the evolution of supernovae. Without the arguments and counterchallenges, it could be argued (!) that the learning curve could have been somewhat less steep, but this is an inevitable part of what makes humankind what it is and what it will continue to be. The works of these great scholars represent examples of how the recording, examination, and interpretation of texts written throughout the centuries have been perceived by those around at the time they were written, and by those using hindsight, new insight, and research to draw conclusions that may well have not been so evident during the time of their composing. A commonly running thread throughout, though, is the astonishing and perhaps at times underrated and overlooked input made by the Chinese who, for their part in the collection of observational data, made priceless contributions without which many questions would have remained unanswered.

6.  Mercury Transitions The Planet Mercury Mercury is a curious little world and still presents astronomers with a great many questions. The smallest and innermost planet of our Solar System offers little to the naked eye, and without superior telescopic capability, little to the observer. With an orbital period around the Sun of just 87.97  days and speeding through space at nearly 47  km per second, this planetary representation of a Roman deity is the quickest of any planet to orbit the Sun. Yet, it is our very Sun that has led science to find out a great deal about Mercury beyond the information gathered from various missions to the planet and ground-based observations. For it is the Mercurian transits that have given us great insight into this tiny world measuring just 4878 km in diameter, comparable to the size of the continental United States. Its size makes Mercury around two-fifths the size of Earth and smaller than Jupiter’s moon Ganymede and Saturn’s moon Titan. Mercury has a mean radius of 2440 km, and its circumference at the equator measures 15,329 km. Mercury was believed to have once been a bigger body, but as the planet cooled, it contracted, and this shut off the surface lava flows. As the planet transitioned from molten to solid, Mercury contracted radially as much as 7  km since its birth 4.5  billion years ago. It is a very dense world, the second densest in the Solar System, with only Earth being denser. A day on Mercury lasts 58 Earth days, with 176 days taken for the Sun to return to the same spot in the sky, as seen from a fixed point on the surface (Mercury solar day). Its thin atmosphere includes oxygen (42%), sodium (29%), hydrogen (22%), helium (6%), and trace gases. Mercury’s size makes it too weak to hold on to a significant atmosphere, thus leaving it defenseless against the incoming heat from the Sun, with the planet boasting some of the most varying temperature swings in the Solar System. Daytime temperatures can reach 800 degrees Fahrenheit, dropping to −290 degrees at night as the © Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_6

81

82

6.  Mercury Transitions

atmosphere fails to retain any of the heat from the severe daytime value, rapidly allowing it back into space. Despite these extremes, Mercury still might have water-ice at its north and south poles inside deep craters, but only in regions of permanent shadow. There, it could be cold enough to preserve water-ice away from the searing temperatures on sunlit parts of the planet. Mercury has a highly eccentric egg-shaped orbit that takes the planet as close as 47 million km and as far as 70 million km from the Sun. For a time, it was thought that another planet existed in an orbit between Mercury and the Sun. The planet Vulcan was the vision of French astronomer and mathematician Urbain Le Verrier (1811–1877). Le Verrier, whose most famous achievement was his prediction of the existence of the then unknown planet Neptune, using only mathematics and observations in respect to the known planet Uranus, suggested Vulcan existed in order to explain the peculiarities of Mercury’s orbit. Despite occasional claimed observations from a number of astronomers who took it upon themselves to find Vulcan, no such planet was ever confirmed. Other suggestions to account for Mercury’s orbit were proposed, including a field of asteroids, or a large field of dust near the planet. As observations revealed nothing to substantiate these claims, these too were duly dispensed with. The orbital discrepancies were eventually explained by Albert Einstein’s (1879–1955) theory of general relativity. It transpired that where people were going wrong was actually looking for objects. Einstein eventually revealed that they should have been looking at space itself. In his theory of relativity, Einstein showed that mass warps space. This warping didn’t noticeably affect planets far from the Sun, but Mercury was so close that its strange precession was visible as soon as people started paying close attention. Sir Isaac Newton’s (1643–1727) law of gravitation was pretty accurate. It predicted the planetary orbits so accurately that it noticed a certain anomaly in observed orbits, predicted the existence of a far-off planet perturbing those orbits, and told astronomers to point their telescopes there. That allowed them to find Neptune in 1846. However, Mercury, whose orbit was referred to as the anomalous precession of Mercury, defied explanation until Einstein’s theory accounted for the strange orbit. Einstein said that the Sun’s gravitational field is so strong at Mercury’s orbit that it has a significant effect on spacetime, dragging Mercury with it. His prediction precisely explained the difference between observation and Newtonian theory, and is hailed as one of the three classical

The Planet Mercury

83

tests of general relativity – the other two being the bending of light in gravitational fields and the gravitational redshift. Many planets are known to spin east to west, others west to east, with some not spinning at all. Those that don’t are said to be tidally locked, always showing the same face, such as the Moon does with Earth. One side is cold, the other hot, with no alternating between the two as a spinning planet would dictate. It is thought that at one time Mercury was tidally locked with the Sun, and that a large body, probably an asteroid, struck the planet, causing it to spin. Before the impact, it is also believed that Mercury, like Venus, had a retrograde spin, east to west, slowing over millions of years until it spun no more. Then, following the strike – believed to be shown by the Caloris Basin feature, the largest impact crater on the planet – Mercury started rotating again, but this time in the opposite direction, west to east. Mercury, also like Venus, has no moon, although during the 1970s, one was briefly thought to exist, but ultimately it turned out to be misinterpreted data from a star. Observation of such a moon from Earth would be extremely difficult, given its probable size and Mercury’s closeness to the Sun. There are many factors working against Mercury having or ever having had its own moon, these being determined by the three causes of how a planet gains a natural satellite. In the first instance, a moon, or moons, may form from a circumplanetary disk of material that orbits a planet, similar to a protoplanetary disk around that of a star. In the case of a planet, the disk and all its component material gradually coalesce to form larger bodies, a sort of ‘clumping together,’ which may or may not become massive enough to undergo hydrostatic equilibrium – in other words, become spherical. The same principal applies to the formation of a planet in our own Solar System, just on a grander scale, as gravity tries to meld this greater amount of matter (in excess of 1000  km in size) together, to create the most efficient shape possible, that of a sphere. In 2006, the International Astronomical Union, (IAU) decided that the ability to undergo hydrostatic equilibrium was one of the requirements for an object to be considered a planet. Aside from this, a planet must also orbit the Sun, and needs to have cleared out all the smaller objects in its orbit. However, when discussing the formation of a much smaller body, like that of a moon, the force of gravity trying to pull the object into a sphere isn’t enough to overcome the strength of the rock keeping it in its present shape. When an object has the gravity to pull itself into a

84

6.  Mercury Transitions

sphere, astronomers say that it’s in hydrostatic equilibrium. The question is, was there ever a time in Mercury’s evolution when a moon might have existed, or were the stresses and strains of much more superior gravitational forces, i.e., the Sun, always destined to leave Mercury moonless? The latter surely applies. In the second instance, moons may be acquired when a small body is captured by the gravity of a larger body, as in the case of Mars, which probably acquired its two moons either from the Asteroid Belt, or given the nature of their orbits, simply captured two rocks that happened to be roaming the region during the early formation of the planet. Many moons belonging to Jupiter, Saturn, Neptune, and Uranus were captured in similar circumstances. This leaves Mercury with little room for consideration, with Venus’ lack of a moon to perhaps a lesser extent. Venus, slightly smaller than Earth but much larger than Mercury, did potentially hold the possibility of capturing a moon for itself. However, again, greater and more forceful gravitational attractions were at work. The final instance that could have left Mercury with its own moon for a time involve massive collisions that eventually caused the planet to eject material into space, material that ultimately formed into a moon. Any such collisions, while likely, would have probably spelled the end of Mercury itself, and we must deem its very survival a credit to the planet existing at all, given impacts that took place so close to the Sun. There has been much speculation about whether Mercury itself is a moon that escaped the orbital pull of a larger planet. Our own Moon and Mercury appear similar. However, despite a perhaps passing resemblance, closer inspection reveals great differences. Firstly, there are the “seas” of the Moon, vast plains of once-liquid rock. Mercury, too, shows signs of lava flowing over its surface. In fact, many of its craters are completely buried in it. But Mercury still lacks those obvious oceans of stone that, when gazing at our own Moon, give that familiar face. Another distinction between the two bodies involves the crater rays. The big craters on both the Moon and Mercury formed during violent impacts. Surrounding the younger ones, you can sometimes still see long streaks formed by the ejecta that was blasted from the ground during these massive collisions. The Moon has several sets of brilliant rays, but Mercury’s rays are often even brighter, and in places they are visible stretching across nearly an entire hemisphere. Perhaps the clue to Mercury’s existence and very evolution lies within the planet itself, and its dense make-up. This clue then

The Planet Mercury

85

possibly takes us thousands of miles away to a possible answer in the Kepler-107 system. It is estimated that Mercury’s planetary core must make up around two-thirds of the entire planet – far larger proportionally than any other rocky planets that we know of. So why is Mercury so dense? In the original formation of the planet, its structure may have been created with a larger fraction of lighter, silicate mantle, but during a series of huge collisions this early mantle might literally have been blasted off into space. Kepler-107 is a star in the constellation of Cygnus, “the Swan.” There are four planets orbiting around this Sun-like star, which collectively lie 1714 light years from Earth. While studying Kepler-107 and its four planets labeled Kepler-107b, c, d, and e, astronomers Aldo S. Bonomo and Mario Dalmasso, working at the Instituto Nazionale Di Astofisca (INAF) in Italy, were intrigued by the mass of Kepler-107b and c. In conjunction with astrophysicist Li Zeng of the Harvard-Smithsonian Center for Astrophysics, they delivered an important piece of research that covered new ground with regard to Mercury’s evolution, research that was later published in the journal Nature Astronomy on February 4, 2019. Collectively, these planets, first discovered in 2014, have orbital periods of between 3.2 and 14.8 days, which fit into a pattern of orbital resonances that indicate that these planets originally formed further from Kepler-107, before migrating inwards and becoming locked in their current resonances. As a comparison, take the similar resonance of 4:2:1, the orbital resonance of Jupiter’s large moons Io, Europa, and Ganymede. Using the HARPS-N spectrograph at the Telescopio Nazionale Galileo in La Palma to measure cyclical shifts in Kepler-107’s radial velocity caused by the gravitational pulls of these orbiting planets, they found that although the two inner planets, Kepler-­ 107b and c, have nearly identical radii, the second planet is almost twice as dense as the innermost. This means, just like Mercury, that Kepler-107c must have a huge iron core. After much speculation as to why, Bonomo concluded that Kepler-107c’s dense nature must be due to a huge collision. Such an impact would destabilize the current resonance pattern of the four planets’ orbits, and so it must have occurred early in the system’s evolution, before the planets had finished migrating. So, Mercury is not alone; it has a far-off twin, and as we search the depths of space for more exoplanets, it would be no surprise, given the way in which some planetary systems form, that other examples will come to light.

86

6.  Mercury Transitions

Early Observations of Mercury Mercury is never more than 28 degrees away from the Sun when viewed from Earth, meaning that for observers on Earth, the planet can only be seen in the morning sky to the east, or the evening sky to the west, with its respective elevation making for a challenge to even the most accomplished of observers. When offering its best apparitions, Mercury, like Venus, will sport a complete range of phases as it moves in its inner orbit relative to Earth, a synodic period that reoccurs every 116 days. The earliest known recorded observations are from the Mul-Apin tablets. Mul-Apin is the conventional title given to a Babylonian compendium that deals with many diverse aspects of Babylonian astronomy and astrology. The earliest copy of the text so far discovered was made in 686 b. c. However, the general consensus is that the text was originally compiled around 1000 b. c. The latest copies of the Mul-Apin are dated to around 300 b. c. The text runs to two tablets and possibly a third tablet. The observations relating to Mercury were most likely made by an Assyrian astronomer around the fourteenth century b. c. The cuneiform name (one of the earliest systems of writing, invented by the Sumerians) given to Mercury is translated as meaning “the jumping planet.” Babylonian records, which can be found on Sumerian clay tablets, inscribed in cuneiform, date observations of Mercury back to the 1 millennium b. c. They referred to the planet as Nabu, after the messenger to the gods in their mythology. Nabu is the ancient Mesopotamian patron god of literacy, the rational arts, scribes, and wisdom. The Babylonians recognized five planets in total (Mercury, Venus, Mars, Jupiter, and Saturn), and called them “wild sheep” because of their wandering paths over the fixed backdrop of stars. Nabu, or Nebo, is the god of writing, the record keeper, and just as Mount Sinai in Egypt is named for the Babylonian moon god Sin, Mount Nebo, in present-day Jordan, is named after the Babylonian god associated with the planet Mercury. In Babylonian astronomy, Mercury was associated with both sexes because of its appearance in the evening and morning, with later Babylonian civilizations (600 b. c – a. d. 200) showing advancement in both astronomy and mathematics, leading to a catalog of the stars that form the basis of our zodiac. Their catalog also included detailed observations of the movements of the five visible planets, including Mercury.

Early Observations of Mercury

87

The Greeks gave the planet two names, Apollo for its apparition in the morning sky, and Hermes for its evening appearance, although they actually knew that both were actually the same body. The Greek philosopher Plato (b. c. 428/427 or 424/423– 348/347) and the student of his works, Eudoxus (c.390–c.337 b. c.) reported that the synodic and sidereal periods of Mercury were 110 days and 1 year, respectively. Around b. c. 500, the Greek philosopher Heraclitus (b. c. c.535–c.475) correctly thought that both Mercury and Venus were orbiting the Sun, not Earth. Heraclitus was renowned for his insistence on the ever-present change as being the fundamental essence of the universe, as stated in the famous saying, “No man ever steps in the same river twice.” In Roman mythology, Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the gods. The astronomical symbol for Mercury is a stylized version of Hermes’ caduceus, the “herald’s wand or staff” carried by Hermes in Greek mythology and consequently by Hermes Trismegistus in Greco-Egyptian mythology. The Roman-­ Egyptian astronomer Ptolemy wrote about the possibility of planetary transits across the face of the Sun in his work Planetary Hypotheses. Ptolemy suggested that no transits had been observed because planets such as Mercury were too small to see, or because the transits were too infrequent. In his book Planetary Hypotheses, Ptolemy developed a model of the universe as a whole. Following Aristotle, he conceived it as a set of nested spheres, of which the Sun was set at a radius of 1210 Earth radii, and the outermost, the sphere of the fixed stars, was set at 20,000 Earth radii. Copernicus’ model of the universe places the Sun rather than Earth at the center of the universe. In ancient China, Mercury was known as “the Hour Star” (Chen-xing). It was associated with the direction north and the phase of water in the Five Phases of metaphysics. Primarily known as Wu Xing (“moving”), the system of five phases was used by the Chinese for describing interactions and relationships between phenomena. A planet is called a “moving star” in Chinese, and Wu Xing originally refers to the five major planets (Jupiter, Saturn, Mercury, Mars, and Venus) that create five dimensions of Earth life. According to Wu Xing theory, the structure of the cosmos mirrors the five phases. Each has a complex series of associations with different aspects of nature, with each phase lasting around

88

6.  Mercury Transitions

72 days each. Also known as the Five Elements, modern Chinese, Korean, Japanese, and Vietnamese cultures refer to Mercury as the “water star,” based on one of the elements. Hindu mythology used the name Budha for Mercury, and this god was thought to preside over Wednesday. Budha as a planet appears in various Hindu astronomical texts in Sanskrit (a language of ancient India with a history that dates back about 3500 years). One such fifth century text is that of Aryabhatiya by Aryabhata (a. d. 476–550), a man who was the first of the major mathematician-­ astronomers of the classical age of Indian mathematics and Indian astronomy. Aryabhata offered notable explanations for both lunar and solar eclipses, and reflection of light by the Moon. In his work Aryabhatiya, Aryabhata also correctly insisted that Earth rotates on its axis daily, and that apparent movement of the stars is a relative motion caused by the rotation of Earth, directly contradicting the then-prevailing view that the sky rotated. Astronomers in ancient India believed that the location of the planets in the sky at the time of a person’s birth determined that person’s future. The Hindus called the planets collectively “navagrahs,” and references to them can be found on temple markings. Some of the legacies of Aryabhata are the modern words “sine” and “cosine,” which are actually inaccurate transcriptions of the words jya and kojya as introduced by Aryabhata! India’s first satellite was named in his honor. Launched on April 19, 1975, from Kapustin Yar, a Russian launch and development site in Astrakhan Oblast, it was sent into space to conduct X-ray astronomy experiments, but a power failure after 4 days and then a loss of all contact with the craft after 5 days saw a much earlier than anticipated end to its mission, returning to Earth’s atmosphere on February 11, 1992. Although the god Odin (“Woden” in Old English or “Wotan” in Old High German) of Germanic paganism was also associated with the planet Mercury and Wednesday, the Maya in contrast may have represented Mercury as an owl (or possibly four owls; two for the morning aspect and two for the evening), which served as a messenger to the underworld. With regard to the recording and documentation of the night sky, the importance of the Maya contribution to astronomy cannot be underestimated. When reflecting on methods of recording astronomical data throughout the ages, and in relation to this book, the Maya codices present themselves as a remarkable piece of work. The codices (or codex singular) were written by the pre-Columbian Maya civilization in Maya hieroglyphic script on

Early Observations of Mercury

89

Mesoamerican bark paper, and the wealth of knowledge they contain is priceless in our understanding of how they perceived the universe. The pre-Columbian era literally refers to the time preceding Christopher Columbus’s voyages of 1492. Along with the Maya, many civilizations had established permanent settlements with great feats of architecture, an advanced method of agriculture, and a complex societal hierarchy. The books produced by the Maya are as integral to the fabric of their society as any part, for in these folding books, we see the products of professional scribes working under the patronage of deities such as the Tonsured Maize God and the Howler Monkey Gods. Maya astronomy is thought to have developed in the period from 1500 to 800 b. c., and much of what we know is found in the writing of one particular codex, the Dresden Codex. Of the codices that survived, of which only 20 are known to exist from ancient Central American cultures, the Dresden Codex is generally considered the most important. The codices are written on amate, a type of bark paper, which was extensively used for communications, records, and rituals during the Triple Alliance (a gathering of the Aztec Empire from three city-states, borne out of bitter civil wars). The paper was obtained from the bark of a wild-growing species of fig tree. The Dresden Codex, a band of paper 3.5 m long arranged in 39 sheets, has been fascinating historians and astronomers alike for centuries, for this particular codex is an ancient encyclopedia of astronomical observations. It contains information regarding the calendar system, astronomical data and sky mechanics, as well as tables of multiple integers thought to have been used in the calculations of planetary movements. The Maya were extremely interested in Venus, believing it to be as important as the Sun. But the Maya charted the motion of Mercury as well, detailed observations of which are contained in the Dresden Codex. The Maya made observations of the visibility of Venus, from when it had appeared for the first time after its conjunction with the Sun as a morning star in the sky shortly before sunrise, or after its upper conjunction, when it had appeared in the sky as an evening star shortly before sunset. With regard to Mercury, there is a similar pattern of documentation, with observations of Mercury’s visibility, and also its trajectory, which creates an eccentric ellipse. The Maya, whose observations were carried out using only simple measuring methods, could have only observed Mercury when the planet attained

90

6.  Mercury Transitions

its greatest angle of distance during its circuit around the Sun, the so-called elongation, as observations at any other time would have been hindered by the Sun. The Maya also calculated that Mercury would rise and set in the same place in the sky every 2200 days. In medieval Islamic astronomy, the Andalusian astronomer Abu Ishaq Ibrahim al-Zarqali (1029–1087) in the eleventh century described the deferent of Mercury’s orbit as being oval, like an egg or a pignon (pine nut), although this insight did not influence his astronomical theory or his astronomical calculations. An instrument maker, astrologer, and the most important astronomer from the western part of the Islamic world, Al-Zarqali wrote two works on the construction of an instrument known as the “equatorium,” used for computing the position of the planets using diagrams of the Ptolemaic model. The earliest extant record of a solar equatorium, that is, one to find the position of the Sun, is found in Proclus’s fifth century work Hypostasis. Proclus was one of the last classical philosophers, and he gives instructions in Hypostasis on how to construct one using either bronze or wood. Al-Zarqali also invented a kind of astrolabe known as “the tablet of Al-Zarqali,” which was famous in Europe under the name Saphaea. There is also a reference to Al-Zarqali having constructed a water clock, although opinion seems to suggest it was someone else of the same name. In the twelfth century, Arab Andalusian polymath Ibn Bajjah (c.1085–1138) observed “two planets as black spots on the face of the Sun,” which was later suggested as the transit of Mercury and/ or Venus by the Maragha astronomer Qotb al-Din Shirazi (1236– 1311) in the thirteenth century. However, Ibn Bajjah could not have witnessed a transit by Venus, as there were no Venus transits in his lifetime. It could have been sunspot activity, but it could equally have been a transit of Mercury. However, it is considered that most such medieval reports of transits were really observations of sunspots. In India in the fifteenth century, mathematician and astronomer Nilakantha Somayaji (1444–1544) developed a partially heliocentric planetary model in which Mercury orbits the Sun, which in turn orbits Earth, similar to that of the system proposed by Tycho Brahe in the late sixteenth century. One of Somayaji’s most influential works was that of the Tantrasamgraha, which completed in 1501. His work revised Aryabhata’s model for Mercury and Venus. His equation for the center of these planets remained the most accurate until the time of Kepler in the seventeenth century.

Transits of Mercury

91

Transits of Mercury The first telescopic observations of Mercury were conducted by Galileo Galilei in 1610. Despite observing the phases of Venus, his telescope was not powerful enough to discern those of Mercury. Through his crude refractor it remained a point of light, with no detail on the Mercury’s disc or anything to discern of note from the innermost planet. However, let us not forget what Galileo did observe, and how his findings revolutionized astronomy. One of the most important findings was the discovery of craters and mountains on the Moon, which not only gave scientists a view that such topography can be related to instances on Earth, but for the first time gave absolute proof that the Moon was not a smooth sphere, as many believed. Aside from Jupiter and its moons, the phases of Venus, and sunspots, his discoveries challenged many common beliefs about the bodies that occupy our Solar System, rewriting centuries’ worth of theories with hard, solid fact (Fig. 6.1). However, it wasn’t until French mathematician and astronomer Pierre Gassendi (1592–1655) that the first telescopic observations of the transit of a planet across the Sun were made, when he saw a transit of Mercury, as predicted by Kepler. In 1639, Italian astronomer, mathematician, and Jesuit priest Giovanni Battista Zupi (1590–1650) was the first person to discover Mercury had orbital phases, like those of the Moon and Venus. This d ­ iscovery occurred 30 years after Galileo’s first telescope design, with Zupi’s own telescope capabilities only slightly more impressive. Aside

Fig. 6.1.  Mercury transit, May 9, 2016. Solar Dynamics Observatory (Courtesy of NASA)

92

6.  Mercury Transitions

from the finding, it demonstrated conclusively that Mercury orbited the Sun. Of all the records and observations that have been recorded, there remains a special place for the documentation of the extremely rare events in astronomy. Such a rare event is the passage of one planet in front of another (occultation) as seen from Earth. Mercury and Venus occult each other every few centuries. The next occultation of Mercury by Venus is scheduled for December 3, 2133. Astronomer John Bevis recorded the event of May 28, 1737, the only one historically observed. However, even that is possibly overshadowed by another achievement attributable to Bevis, the discovery of the Crab Nebula in 1731! It’s incredible to contemplate just how rare a Venus-Mercury occultation is. Given the necessary timing accuracy of seeing one planet’s disk covering another is one element, but add in the fact that the orbits of Earth, Mercury, and Venus are tilted with regard to each other, and the chances grow still more remote that all three will align in exactly one position. History tells us that the last time for such an occurrence to happen before that of Bevis’ observation was August 20, 796, with both planets only 5 degrees from the Sun. Bevis, who also compiled a star catalog entitled Uranographia Britannica, was only one of two persons known to have observed Halley’s Comet on its first predicted return in 1759. Bevis observed the comet on May 1 and May 2 after its perihelion. The other observer was also a physician, Nicholas Munckley, who saw it on the same dates. Bevis was also responsible for formulating a prediction rule for the eclipses of Jupiter’s moons. From 2000 to 2199, there will be 27 transits of Mercury, whereby the innermost planet passes in front of the solar disk. Rare indeed, but not as rare as Venus transits, with only two this century – in 2004 and 2012. Transits of Mercury this century can happen from May 7–10 and November 7–14. The November transits occur about twice as often as the ones in May. The reason for this is because during a May transit, Mercury is close to aphelion, farthest away from the Sun, whereas during a November transit, it is closest to the Sun, at perihelion. This is also why Mercury appears a fraction larger during May transits. Transits of Mercury are gradually shifting to late in the year. Indeed, before 1585, they occurred in April and October.

7. Mapping the Sky, From Shi Shen to Charles Messier Whereas our earliest of ancestors tended to draw particular events or erroneous happenings in the night sky – the passage of a comet, the outburst of a star, or the darkening of the light during an eclipse – the importance of making accurate and detailed maps of the night sky became almost second nature to future generations who studied the stars, either for astrological purposes or weightier scientific understanding. Over the centuries, the changes in belief systems and the enhancement of our understanding has meant that the complexity of the maps has continually been developed and augmented into a more detailed and more lavish mirroring of the heavens, but the fundamental basics that are still being recorded maintain the reason for capturing the stars and constellations, because at night they appear, and no matter who we are or what we represent, for some, there is a need to put one’s own stamp and mark on the stars above, a sole-searching definition of ultimately what the heavens mean to the person documenting them. Whether it be our ancient ancestor simply sketching the ever-changing points of light in the sky, the amateur astronomer focusing in on the detail of a binary star to show others within an astronomical group, or the astronomer making size calculations and associated measurements, being at one with the night sky and how we perceive the heavens is all very personal. Star catalogs have meant many different things to many different cultures, but trace back the lines and the reality remains that it’s all down to the individual. The Babylonians, Greeks, Chinese, Persians, and Arabs all made great efforts to record the seasonal changes with star catalogs, basically a list of stars, often accompanied by a star chart for illustration. Therefore, from our very past and deep into the future, mapping of the skies will continue as each time period forges its own link to how it perceives, understands, and records the night sky. However, once a canvas for the eye of the observer to fill and © Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_7

93

94

7.  Mapping the Sky, From Shi Shen to Charles Messier

record stars, the mapping has entered a different phase, as we see farther and are able to find more and more distant objects. The once Spartan-looking canvas that merely reflected the brightest stars and constellations has transformed into a lavish tapestry that with every stroke of its current ‘artist’ custodian has been added to and enhanced. Over the centuries, there have been notable contributions that reflect the curve of understanding when making ­cartographical references to the night sky, some of which take the form of star tables. Some predominately feature a more statistical overview, others taking the form of text and drawings. The earliest known star chart was drawn 5000 years ago by the Indians in Kashmir; this chart also depicts a supernova for the first time in human history. The oldest known star constellation record may be that found on a carved ivory mammoth tusk drawn by the early people of Asia, dating back some 32,500 years ago and said to resemble the constellation of Orion, the Hunter, as discussed earlier in this book. The oldest accurately dated star chart appeared in ancient Egyptian astronomy in 1534 b. c. The Babylonians recorded the presence of celestial objects during the early history of Mesopotamia, a historical region of western Asia. Their records, inscribed in cuneiform (wedge-shaped markings on the clay tablets), date from approximately 3500–3200 b. c. As the capturing of the skies evolves, a shift to more lavish, intricate, and detailed work is obvious, before the advent of computers and the shift to 3-D modeling of the night sky, with accompanying graphics and text. What route the “art” of sky atlas making takes the astronomer next is open to debate, with that question probably posed after each great work down the centuries was completed, each person confident that his or her work was the defining picture of all that we see in the night sky. Each though, one by one, no matter what length of time the work took, was eventually superseded by improved and more detailed versions. This begs the question: “How will our current interpretation be superseded, by what means and by whom?”

The Greeks References to stars and constellations appear as far back in archaic Greek astronomy as Homer, author of Odyssey and of the IIiad, both written during the time of the Trojan War. Aside from Homer,

The Greeks

95

references to the heavens are also documented in the writings of Hesiod, active around 750 and 650 b. c., around the same time as Homer. In both the Odyssey and the IIiad, references are made to the constellation of Bootes, Ursa Major, and Orion. There are also references to the Hyades star cluster in Taurus, and the star Sirius. Hesiod makes a reference to the star Arcturus in Bootes, although all of the attributable astronomical mentioning is completely ­non-­scientific, aside from a loose association to cosmology and perhaps more aligned with any tenuous link to astronomy, that of the rising and setting of certain stars at sunrise and sunset. In the timeline that charts significant and important contributions to the making and recording of star catalogs, charts, and tables, the star catalog contributed by Greek astronomer Hipparchus (c.190-c.120 b. c.) is a notable marker in history. Written fairly late in his career, Hipparchus was also able to construct a globe depicting the constellations, based on his own observational work. The work of Hipparchus was subsequently updated by Claudius Ptolemy in his Almagest, later by Persian astronomer Abd al-­ Rahman al-Sufi, and then later again by Nicolaus Copernicus. The Almagest, a. d. c.150, is considered one of the most influential scientific texts of all time. Written by astronomer Claudius Ptolemy, the Almagest is the only surviving treatise on astronomy. The work, giving the accepted model of the universe for the next 1200 years, is also a key source of information with regard to how the Greeks perceived and documented the skies at that time. The Almagest in an earlier form was called Syntaxis Mathematica or Almagestum in Latin, before becoming known as Magna Syntaxis (“The Great Treatise”), and the superlative form of this (ancient Greek: magiste, “greatest”) lies behind the Arabic name al-majisti, from which the English name Almagest derives. The Almagest contains the last-known star table from antiquity, its covers filled with table after table of data, a companion to use in predicting the locations of stars. Compared to earlier astronomy, the book is much more focused on serving as a useful tool than that of presenting a system of astronomy for describing the nature of the heavens. There has been much debate around the Almagest and the star catalog compiled by Hipparchus. The debate surrounds the suggestion that the Almagest is almost entirely Hipparchan, casting doubt over the work of Ptolemy. Ptolemy has been accused by astronomers of fraud for stating that he observed all of the stars

96

7.  Mapping the Sky, From Shi Shen to Charles Messier

referenced by Hipparchus in his work; for almost every star, he used Hipparchus’s data, making positional data corrections to account for a different time period of observation. However, to put this into context, Hipparchus himself probably compiled a list of observations recorded by the Babylonians. The earliest known work of the ancient Babylonian astronomers dates back to the Kassite Period (c.1531–1155 b. c.). The Kassites were people of the ancient Near East, home of early civilizations within a region roughly corresponding to the modern Middle East. The Kassites controlled Babylonia after the fall of the old Babylonian empire.

The Egyptians From the existing records of the Egyptians, it is known that they only recorded a few identifiable constellations and a list of decans that were used as a star clock. The decans are 36 groups of stars making up small constellations. These constellations rose consecutively on the horizon throughout each Earth rotation. Acting as a star clock, the rising of each decan marked the beginning of a new decanal “hour” of the night, and they were used as a sidereal star clock beginning by at least the 9th or 10th dynasty (c.2100 b. c.). The Egyptians called the circumpolar star “the star that cannot perish,” as it was never to set, and although they made no known formal star catalogs, they nonetheless created extensive star charts of the night sky, which adorn the coffins and ceilings of tomb chambers. The Egyptian pyramids were carefully aligned to the pole star, and the temple of Amum-Re, a major Egyptian deity, at Karnak was aligned on the rising of the midwinter Sun. Because of the precession of the equinoxes, the pole star at the time was Thuban, a faint star in the constellation of Draco. The precise orientation of the pyramids serve as a lasting demonstration of the high degree of technical skill the Egyptians possessed in watching the heavens. Because a new decan appears heliacally every 10 days (that is, every 10 days, a new decanic star group reappears in the eastern sky at dawn right before the Sun rises, after a period of being obscured by the Sun’s light), the ancient Greeks called them dekanoi, or “tenths.” The ancient Indian sage Parashara uses drekkana in his system of astrology, which corresponds to the modern idea of the decan.

The Egyptians

97

The system of 36 decans accounted for 36 × 10 to equal 360 days, with 5 days added to compose the 365 days of a solar-­based year. As established, decans measure sidereal time, and the solar year is 6 h longer; the Sothic and solar years in the Egyptian calendar realign every 1460  years. A Sothic year is about a m ­ inute longer than a solar year. The Sothic cycle, also referred to as the Canicular period, covers 1461 Egyptian civil years, or 365 days each, or each 1460 Julian years. The Julian calendar, proposed by Julius Caesar, was a reform of the Roman calendar, taking effect from January 1, 46 b. c. During a Sothic cycle, the 365-day year loses enough time that the start of its year once again coincides with the heliacal rising of the star Sirius, July 19 in the Julian calendar. Sirius was a very important star for the ancient Egyptians, with an enormous amount of activity based upon its arrival, with an array of documentation referencing a point when the star returned to the night sky. Majorly, the return heralded the annual flooding of the Nile. However, because the civil calendar was exactly 365 days long and did not incorporate leap years until 22 b. c., its months “wandered” backwards through the solar year at the rate of about 1 day in every 4 years. This almost exactly corresponded to its displacement against the Sothic year as well. It is fair to say that a great deal of debate surrounds the intricacies of how the anomalies are accounted for, especially considering the ancient Egyptians had three types of ‘years,’ solar, lunar, and seasonal. The first as established was based on the helical rising of the star Sirius, the second was a count of the annual lunar cycles, and the last was the number of seasons, of which there were three in the Egyptian year. Egyptian astronomy can be traced back to prehistoric times, in the Predynastic period. This is a period from the earliest human settlement to the beginning of the early dynastic period, around 3100 b. c., starting with the first pharaoh, Narmer, although some Egyptologists are divided over this, preferring one of two others, either Hor-Aha or Menes. The Predynastic era is traditionally paralleled to the final part of the Neolithic period, beginning c.6000 b. c. and ending in the Naqada III period c.3000 b. c. In the 5th millennium b. c., the stone circles at Nabta Playa may have been used for astronomical alignments. Nabta Playa was once a large internally drained basin in the Nubian Desert, located approximately 800 km south of modern-day Cairo. The site itself is one of the earliest of the Egyptian Neolithic period, and is dated to circa 7500 b. c.

98

7.  Mapping the Sky, From Shi Shen to Charles Messier

Although today the western desert is dry, there is more than sufficient evidence to suggest that during several periods in the past, the area was a savanna, supporting numerous animals such as extinct buffalo and large giraffes, varieties of antelopes and gazelle. By the 7th millennium b. c. exceedingly large and well-organized settlements were to be found in the region, relying on deep wells for sources of water. It is thought huts were constructed in straight rows. Food sources at the time included fruit, legumes (fruits or seeds of a plant such as a pulse or lentil), cereal crops, and tubers (stems or roots of plants), with the later introduction of goats and sheep that were imported. The citizens of the time fashioned what is considered to be among the world’s earliest known archaeoastronomical devices, including the alignment of stones that may have indicated the rising of certain stars that, on arrival and in the form of a “calendar circle,” would have given the approximate direction of a summer solstice sunrise. Although there remains some debate of the use of the term “calendar circles,” because of the spaces between the pairs of stones being too wide, and there being some anomalies linked to the ability to make accurate calendar measurements, the site parallels contemporaries of its time, such as the Goseck circle in Germany and the Mnajdra megalithic temple complex in Malta. The Goseck circle has been dated to approximately the forty-­ ninth century b. c., remaining in use until about the forty-seventh century b. c. The circle, which consists of a concentric ditch 75 m across and two palisade rings containing entrances in places aligned with sunrise and sunset on the winter and summer solstice days, is thought to be the oldest and best known of the circular enclosures associated with the central European Neolithic era, incorporating similar constructions. These alignments with the winter and summer solstices are the only evident astronomical alignments in the remains of the structure, with only speculation in regard to other possible usages. The term “solar observatory” has been linked with the site, but again, debate remains as to whether or not that is an accurate description, with other aspects potentially possibly pointing towards a lunar calendar as well. However, not enough evidence exists to support either hypothesis. The Mnajdra temple complex can be found on the southern coast of Malta. Its construction dates back to the 4th millennium b. c. The complex is among the most ancient religious sites on Earth, heralded by the World Heritage Sites committee as a “unique architectural masterpiece.” The lowest temple at the site

The Egyptians

99

is astronomically aligned and was thus probably used as an astronomical observation and/or calendrical site. On the vernal and the autumnal equinox, sunlight passes through the main doorway and lights up the major axis. On the solstices, sunlight illuminates the edges of megaliths to the left and right of this doorway. Astronomy also played a considerable part in religious affairs for the Egyptians, upon which the fixing of dates for festivals were linked. The titles of several temple books are preserved, recording the movements and phases of the Sun, Moon, and stars. One of the most important astronomical texts was the Book of Nut (originally titled “The Fundamentals of the Course of the Stars”). The book is a collection of ancient Egyptian astronomical texts, which aside from the covering of various mythological subjects, focuses on the movements of not only the Sun and the Moon but on the planets as well, with references to sundials and related matters. The title was given to the book because of the depiction of the sky goddess Nut arching over the Earth in some copies of the text. She was mostly depicted as a star-covered nude woman, but other depictions show Nut in the form of a cow whose great body formed the sky and heavens, also as a sycamore tree, or as a giant sow, suckling many piglets (the piglets representing the stars). Nut is shown in some depictions to be supported by the god of air, Shu. The Book of Nut texts include material from different periods of Egyptian history, with nine different copies of the book covering various dates. Three copies are found on monuments, and six more are found in papyri of the second century a. d., from the temple library in ancient Tebtunis, a town in the southern Faiyum Oasis, a basin the desert immediately west of the Nile south of Cairo. Also, in religious affairs, the death of a king had a strong connection to the stars with the deceased king’s soul rising to the heavens to become a star. Translated pyramid texts describe the king ascending and becoming the Morning Star among the Imperishable Stars of past kings. Beginning with the 9th dynasty, ancient Egyptians produced ‘diagonal star tables,’ which were usually painted on the inside of wooden coffin lids. The practice continued until the twelfth century. These diagonal star tables or star charts are also referred to as “diagonal star calendars” or “decanal clocks.” The star charts featuring the paintings of Egyptian deities, decans, constellations, and star observations are also found on the ceilings of tombs and temples. Following the study of such star charts, Marcobius Ambrosius Thoedosius (a. d. 395–423) attributed the planetary

100

7.  Mapping the Sky, From Shi Shen to Charles Messier

theory wherein Earth rotates on its axis and the interior planets Mercury and Venus revolve around the Sun, which in turn revolve around Earth, to the ancient Egyptians. He therefore named it the “Egyptian system,” although no direct and conclusive evidence exists that it was known in ancient Egypt. A seemingly intriguing character of whom not a great deal is known aside from his writings, Marcobius has a prominent lunar crater named in his honor, a 63-km-wide crater positioned northwest of the Mare Crisium. Following Alexander the Great’s conquests and the foundation of Ptolemaic Egypt, the native Egyptian tradition of astronomy merged with Greek astronomy as well as Babylonian astronomy. The city of Alexandria in Lower Egypt became a focal point of scientific activity throughout the Hellenistic civilization. The greatest Alexandrian astronomer of this era was a Greek, Eratosthenes (c.276–195 b. c.), who among other achievements calculated the size of Earth, providing an estimate for its circumference. Eratosthenes achieved this by companied angles of the mid-day Sun at two places of a known north-south distance apart. His calculation turned out to be a remarkably accurate one and one that he made without leaving Alexandria. Eratosthenes knew that at local noon on the summer solstice in Syene (modern-day Aswan, Egypt), the Sun was directly overhead. He knew this because the shadow of someone looking down a deep well at that time in Syene blocked the reflection of the Sun on the water. Eratosthenes then measured the Sun’s angle of elevation at noon in Alexandria by using a vertical rod known as a gnomon (from the Greek “One that knows of examines”), the part of a sundial that casts a shadow. He then measured the length of the shadow shown on the ground. Then, using the length of the rod, and the length of the shadow, as the legs of a triangle, he calculated the angle of the Sun’s rays. When he determined the equation in relation to a circumference of a circle, and taking into account that Earth is spherical, plus knowing both the distance and direction of Syene, he concluded that Earth’s circumference was 50 times that distance. Eratosthenes was also the first to calculate the tilt of Earth’s axis, again with a remarkable level of accuracy, along with the diameter of the Sun. It is also thought that during his illustrious career he also accurately calculated the distance from Earth to the Sun, and indeed invented the leap year. The latter came around during his time spent at the library in Alexandria, where he devised a calendar using his predictions about the ecliptic of Earth, calculating that there are 365 days in a year and that every fourth year there should be 366 days.

Ancient Chinese

101

A mathematician and geographer, Eratosthenes is responsible for actually inventing the discipline of geography, including much of the terminology in use today.

Ancient Chinese The first Chinese records of astronomy date from around 3000 b. c. The first human record of an eclipse was made in 2136 b. c., and, over hundreds of years of advanced sky-watching and the making of detailed and accurate records, the Chinese became very adept at predicting lunar eclipses. The Chinese used circumpolar stars as their reference point for the heavens, unlike the Indo-Europeans, who used observations based upon the rising and setting of celestial bodies on the ecliptic and the horizon. The circumpolar constellation of the Big Dipper was used to mark the passage of time and the seasons, using the position and orientation of the formation relative to the pole star during any given evening. Although making detailed studies of the sky and keeping records of observational work incorporated the main body of the astronomer’s work, it was not at the core of their duties, with the Chinese obsession for accurately charting time. Astronomers had to announce the first day of every new month and predict lunar eclipses. Although meticulous studies of the sky allowed them to do this with more than a fair degree of accuracy, the failure to do so would often result in dire consequences for the astronomer who got it wrong, in most instances being beheaded for their mistakes. To make their calculations, Chinese astronomers developed a process whereby the sky was equally divided into 12 branches and 10 stems, all arranged around the ecliptic, these presenting astronomers with a 60-year cycle. The credit for the implementation of this system lies with Emperor Huang Ti, or the “Yellow Emperor,” Huang meaning “yellow,” whose reign began in about 2607 b. c. It is thought that he was also responsible for the building of a great observatory and planetarium, which were constructed in order to make observations more accurate. Huang Ti’s reign is a legendary one, also being credited with the introduction of wooden houses, carts, boats, and the bow and arrow. Writing and the use of coined money was also accredited to his reign. His wife, too, was said to have discovered sericulture, silk production, and was said to have taught women in society of the era how to breed silkworms and weave fabrics of silk.

102

7.  Mapping the Sky, From Shi Shen to Charles Messier

The accuracy of the recordings has become legendary throughout the world, with ancient Chinese astronomers making detailed studies of such phenomena as comets, sunspots, solar flares, and novae, all of this long before any other culture had done so. The time given to study also included an attempt to catalog every single star in the night sky, defining the constellations by one governing bright star, which they referred to as the king, with all the fainter associated stars within the grouping known as princes. One such master of cataloguing the skies was astronomer Shi Shen (fourth century b. c.), who is credited with the earliest intentional sunspot observation. Shen also accurately noted the positioning of 121 stars, his work recorded in texts including an eight-volume Astronomy, the one-volume Celestial Map, and the one-volume Star Catalogue of Shi. The latter two are believed to have been written by a school of Shi Shen followers. However, the survival of the texts by Shen are critical in our understanding of how the Chinese arrived at making such observations with so much detail. Sadly, much of Shen’s work did not survive the passage of time. To have made such observations during this time, ancient Chinese astronomers must have been equipped with instruments such as the armillary sphere. The sphere, whose variations include the astrolabe, is a model of objects in the sky on the celestial sphere. It consisted of a spherical framework of rings, centered on Earth or the Sun, which represent lines of celestial longitude and latitude and other astronomically important features, such as the ecliptic. This model therefore differs from a celestial globe, which is a smooth sphere whose principal purpose is to map the constellations. The armillary sphere is therefore apparently equipped to do much more that the celestial globe. With Earth at the center, an armillary sphere is known as Ptolemaic, while with the Sun at the center, it is known as Copernican. Shi Shen is also credited with making the earliest surviving sunspot observation, and not by accident, indeed, through a deliberate attempt to observe them. As many historical texts will confirm, a good many observations of certain phenomena are recorded when astronomers aren’t actually attempting to see them; it just happened to be that the cosmos allows, just at that very moment, a glimpse of something else. Often erroneously credited to another Chinese astronomer, Gan De (fourth century), Shi Shen assumed that these spots were in fact eclipses that began at the center of the Sun and spread outwards. However, although this assumption was wrong, he recognized the spots for what they were, solar phenomena.

Ancient Chinese

103

Also known as the Lord Gan (Gang Gong), Gan De is believed, along with Shi Shen, to be the first in history known by name to compile a star catalog, preceded by the anonymous authors of the early Babylonian star catalogs, then followed by the Greek astronomer, geographer, and mathematician Hipparchus, who is the first known in the Western tradition to have compiled a star catalog. The Dunhuang map or Dunhuang star map is one of the first known geographical representations of stars, dating back to the Tang dynasty (618–907). This dynasty was an imperial dynasty of China spanning the seventh to the tenth centuries. Historians generally regard this time as a high point in Chinese civilization, and a golden age of cosmopolitan culture. In its day, the Tang dynasty capital at Chang’an (present day Xi’an) was the most populous city in the world. Chang’an (“Perpetual Peace” in Classical Chinese) was repeatedly used by new Chinese rulers, at one point being renamed during its time to “Constant Peace” under the Xin dynasty, before having its previous name reinstated upon a change of ruler (Fig. 7.1). Chang’an had been settled since Neolithic times, during which the Yanshao culture was established at Banpo in the city’s suburbs. It is interesting to note that in the northern vicinity of the modern Xi’an, the first emperor of China, Qin Shi Huang (259–210 b. c.) of the Qin dynasty (the first dynasty of Imperial China), constructed his famous massive mausoleum guarded by the Terracotta army. Built to protect Qui Shi Huang in the afterlife, and dating from

Fig. 7.1.  Dunhuang star map. (Courtesy of NASA)

104

7.  Mapping the Sky, From Shi Shen to Charles Messier

approximately the late third century b. c., the life-size figures vary in height according to their roles, the tallest being the generals, overseeing more than 8000 soldiers, 130 chariots with 520 horses, and 150 cavalry horses. Work on the Terracotta army is thought to have involved up to 700,000 workers, and started soon after Emperor Qin ascended to the throne, at the age of 13! Before the Dunhuang map, much of the star information mentioned in historical Chinese texts had been questioned as to its validity and accuracy. However, the map provides graphical information of the star observations, and these are part of the series of pictures on one of the Dunhuang manuscripts. These manuscripts are a cache of important religious secular documents, discovered in the Mogao caves of Dunhuang, China, in 1900. The Mogao caves, also known as the Caves of the Thousand Buddhas, form a system of temples 25 km southeast of the center of Dunhuang, a county-level city in northwestern Gansu Province. Interestingly, Dunhuang is situated in an oasis where Yueyaquan (a crescent-shaped lake) and Mingsha Shan (Singing-­Sand Mountain) are found. The mountain is named after the sound of the wind whipping off the dunes, a singing sand phenomenon. Also known as whistling or barking sand, various theories exist to explain the mechanism behind the singing, including type and size of sand particle, with the commonest ‘singing’ frequency emitted around the 450 Hz mark. Aside from its singing, sand has also been known to produce “roaring” and “booming” sounds. Discovered in the “Library Cave,” which had been walled­up since the eleventh century, the cache of documents has been globally dispersed, with the largest collections resident in Beijing, London, Paris, and Berlin. An organization called the International Dunhuang Project exists in order to collaborate efforts to conserve, catalog, and digitize the manuscripts, printed texts, paintings, textiles, and artifacts discovered in the cave for future reference, and naturally as a precious and priceless collection from ancient Chinese history. The Library Cave was ‘unlocked’ by Chinese Taoist Wang YuanIu (1849–1931), when he was engaged in an amateur ­restoration of statues and paintings in what is now known as Cave 16; he noticed a hidden door, which opened into Cave 17, later to be renamed the “Library Cave.” The scroll with the star chart was found among other documents by Hungarian-born British archaeologist Sir Marc Aurel Stein (1862–1943), when he visited and examined contents of the Library Cave in 1907. During his life as

Ancient Chinese

105

an archaeologist, this was to be Stein’s greatest discovery, not that of the star atlas, but along with 40,000 other scrolls, the finding of a printed copy of the Diamond Sutra, the world’s oldest printed text, dating to a. d. 868. In the words of the British Library, the largest national library in the world containing 150–200 million plus items from across the globe, the Diamond Sutra find amounted to “the earliest complete survival of a dated printed book.” Ironically, some controversy surrounds both Yuanlu and Stein. It seems that all of the scrolls were gradually removed from the caves by Stein, slowly winning over the confidence of Yuanlu, who had taken on a caretaker role at the caves. In total, Stein took 24 cases of manuscripts and four cases of paintings and relics. Despite being knighted for his efforts, Stein was dubbed a burglar by Chinese nationalists, who staged protests against him. Because of his involvement in the discovery and sale of the Dunhuang manuscripts to Westerners for a fraction of their value, Yuanlu is both revered and reviled. However, Stein was not the only one to see the potential of the finds in the cave. Sinologist and Orientalist Paul Eugene Pelliot (1878–1945), having fluent command of classical Chinese (one of 13 languages that he spoke), arrived on the scene several months later. Stein had selected rather ‘blindly’ what he believed to be the more valuable scrolls, but with his command of Chinese and numerous other Central Asian languages, Pelliot was able to be more discerning over the remaining material, having a greater understanding of what was valuable and what was not. Only a few publications have ever been devoted to the star map, with select few mentions, one of the first of which was in British historian and sinologist’s Joseph Needham’s (1900–1995) 1959 edition of the book Science and Civilization in China. The publication, which Needham continued to work upon up until his death in 1995, received widespread acclaim. Needham’s initial collaborator on the project, proposed to Cambridge University Press in 1948, was Chinese and Australian historian Wang Ling (1917 or 1918–1994). With continued work on the volumes, a total of 27 volumes already exist. Nearly all other publications besides the great work undertaken by Needham are in Chinese alone. Given that the star map to date remains the world’s oldest complete preserved star atlas, one has to wonder why this is so.+. The first detailed analysis of the star chart was performed by a team of scientists led by French astrophysicist Jean-Marc Bonnet-­Bidaud (born 1950). Bonnet-Bidaud, the author of the first

106

7.  Mapping the Sky, From Shi Shen to Charles Messier

scientific study of the map, also known as the S.3326 manuscript, is a specialist in high-energy astrophysics and in the study of highly condensed stars and very active in the field of the history of astronomy. The research revealed that the chart contains more than 1300 stars and was composed around the period 649–684 b. c. The team, using precise mathematical projection methods, discovered that the chart shows a remarkable level of accuracy for the brightest star positions. The positions of the brightest stars have been measured using a high-resolution digitized copy of the document and compared to the predicted positions using various projection methods. The scroll, which uses very thin Chinese paper, measures a total length of 3940 mm and a width of 244 mm, and is inscribed on one side only. The beginning of the scroll sadly is missing, depriving us of the title and the author’s name. The entire document is divided into two different parts. The first section is an uranomancy text (divination of the stars, astrology), containing drawings of clouds and different shapes. This is followed by the detailed star atlas consisting of 12 rectangular panels along the celestial equator ending with a circular map of the polar region. More than 1300 stars are distributed in 257 Chinese constellations, according to the very long Chinese tradition described in earlier star catalogs. In particular, three different colors are used for the stars, to distinguish between the three ancient catalogs in use during the Warring States period (461–221 b. c.). Also referred to as the Contending States period, this was an era of great division in ancient China, where seven or more small feuding Chinese kingdoms clashed during one of the most notable times in Chinese history. Not only did it see the rise of great philosophers, including the Confucian thinkers Mencius (372–289 b. c. or 385–303/302 b. c.) and Xunzi (300–230 b. c.), it also witnessed the establishment of many of the governmental structures and cultural patterns that were to characterize China for the next 2000 years. The three colors represent the “Three Schools of Astronomical Tradition,” plus a miscellaneous fourth. • • • •

Black: Chinese Astronomer, Gan De Red: Chinese Astronomer, Shi Shen White: Chinese Astronomer, Wu Xian Yellow: Other Chinese Astronomers.

The document is very finely designed by hand, with most of the asterisms labeled with their names. Despite the loss of the beginning of the scroll, in the first part of the document there is clear

The Persians

107

mention of a comment by Chinese mathematician and astronomer Li Chunfeng (602–670 b. c.), who could possibly be the author. The epoch is also indicated by the position of the pole on the circular chart. However, the final proof came from a particularity of Chinese tradition and writing called the “taboos” characters. During the reign of any emperor, characters that made up the emperor’s personal name were not allowed to be used in their standard form. The characters were changed slightly – usually by omitting or adding a stroke. This is known as the “taboo” form of the character. From this, it was possible to deduce that the documents were produced after the reign of the Taizong emperor Li Shimin (598–649, who reigned 626–649) and before the Ruizong emperor (662–716, who reigned 684–688). It was clear from the study of the Dunhuang star map that the atlas was not a simple or hastily hand-made reminder but established according to precise geometric rules. The projection methods used are very similar to the ones used today to produce our modern maps, showing not only a great advancement for their time but an advancement that incorporated such a high degree of accuracy. To date, no earlier representation of this kind is known to have survived the ravages of times, and while earlier charts have undoubtedly been drawn up by the likes of Chinese astronomer Chen Zhou (220–280), no such document remains. However, despite there being no apparent catalog, it is firmly believed that Chen Zhou collected the works of earlier astronomers of the Han dynasty and combined them into a single system. His catalog listed 1464 stars in 283 constellations, but over the course of history, the work has been lost.

The Persians Persian astronomer Abd al-Rahman al-Sufi is one of nine noted Muslim astronomers, most notable for his contribution entitled the Book of Fixed Stars. Abd al-Rahman al-Sufi, better known as al-Sufi, published the work in 964, with contents including text and pictures. He also translated and expanded on the work accomplished by the Greeks, especially Ptolemy’s Almagest, to which he made several corrections in cases that were at odds with the brightness and magnitude that Ptolemy had noted. The work undertaken to connect that of the Greek with the traditional Arabic star names and constellations was an arduous one, with al-Sufi encountering difficulty in melding the two.

108

7.  Mapping the Sky, From Shi Shen to Charles Messier

As a major translator of the Hellenistic work, it was a challenge in producing the Book of Fixed Stars in so much as managing to balance the perspective and interpretation of two cultures. The outcome was a work that from his own observations included the stars, their positions, their magnitudes, and color, with his findings neatly presented with a text on the constellation and two accompanying drawings, one from the outside of a celestial globe, and the other from inside (as seen from Earth). Al-Sufi identified the Large Magellanic Cloud (LMC), which we now know to be an irregular dwarf galaxy, as is the case with the Small Magellanic Cloud (SMC). His observations of the clouds are the first known written record in existence to document them, with al-Sufi referring to the LMC as al-Bakr (the Sheep) “of the southern Arabs.” He noted that the cloud could not be seen from northern Arabia and Baghdad, but could be sighted from the strait of Bab el Mandeb, meaning “Gate of Tears” in Arabic, the southernmost point of Arabia. The strait earned its named from the dangers of traveling upon it, and it remains an important link between the Indian Ocean and the Mediterranean Sea, via the Red Sea and the Suez Canal (Fig. 7.2).

Fig. 7.2. Large Magellanic Cloud. Spitzer Space Telescope. (Courtesy of NASA.)

The Persians

109

The first Europeans to see the Magellanic Clouds were Italian explorers Peter Martyr d’Anghiera (1457–1526) and Andrea Corsali (1487–1518), at the end of the fifteenth century. Italian explorer Antonio Pigafetta (1491–1531) also sighted them, when accompanying Portuguese explorer Ferdinand Magellan (1480–1521), on his circumnavigation of the world in 1519–1522. Sent by order of King Charles I of Spain, Pigafetta served as Magellan’s assistant and was one of the 18 men who returned to Spain in 1522 out of an ­approximate crew compliment of 240 who had originally set sail on the epic journey. Pigafetta is responsible for writing the first known document concerning the language of Cebuano, an Austronesian regional language. In later years, Spanish missionaries would be writing in the dialect, which is why Cebuano now contains many words of Spanish origin. Magellan was the first European to sail the Pacific Ocean, and indeed around the world, proving that Earth was round. He had the clouds named after him following the later distribution of his writings that were made during the voyage upon seeing the clouds for himself, making the LMC and SMC common Western knowledge. At a distance of 163,000 light-years from Earth, the Large Magellanic Cloud is a satellite galaxy of our own Milky Way, and is ablaze with star-forming regions. Vast clouds of gas within the cloud slowly collapse to form new stars, in turn, lighting up the clouds in an array of magnificent colors. Aside from al-Sufi’s observation of the LMC, he also made the earliest recorded sighting of the Andromeda Galaxy in 964, describing it as a “small cloud.” M31 or NGC 224 is the nearest spiral galaxy to our own Milky Way, at a distance of 2.6 million light years. Whereas al-Sufi was the first person to document the Andromeda Galaxy, German astronomer Simon Marius (1573–1624) was the first person to observe the galaxy with a telescope in 1611. Marius is also most noteworthy for the naming of the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. All four are named after mythological figures with whom Jupiter fell in love. Contrary to probably the vast majority of literature written with regard to the discovery of the four moons, both Marius and Galileo Galilei (1564–1642) claim to have sighted them first. Although logic dictates that both discovered them independently, the two remained at odds for their rest of their lives, Galileo on several occasions accusing Marius in print of plagiarizing his work. Galileo was not the only one to accuse Marius of copying data, with most of Marius’ life being troubled with charges of plagiarizing the

110

7.  Mapping the Sky, From Shi Shen to Charles Messier

work of other scientists. Due to his strong religious beliefs, Marius also never accepted the Copernican model of the universe. Marius, who had studied under astronomer Tycho Brahe, and Galileo also disputed the timing of the building of each other’s telescopes. In 1609, Marius built his own first telescope, slightly before Galileo did himself, although that, too, was a bone of contention. The question remains, who was first to discover the moons? Marius, while in Germany, reported his discovery of the moons in work that he started writing down late in 1609 in the Julian calendar, which translated to January 8, 1610, in the Georgian calendar, in use by Galileo in Italy. A Dutch jury of experts was appointed some 300 years later to validate the claim made by Marius, a claim that Galileo never believed. The findings of the jury validated the claim that Marius independently discovered the moons of Jupiter, but 1 day after Galileo first both saw and wrote down his discovery! Therefore, the credit, as most texts refer to, lies with Galileo, but there are considerations to be addressed. There is no doubt that the names Io, Europa, Ganymede, and Callisto came from Marius (to whom they were suggested by Johannes Kepler). Also, Marius wrote that he had been observing the moons around Jupiter since November 1609 on the Julian calendar, with the use of a neighboring nobleman’s telescope, which would mean he did actually see them first, but because he only later documented his findings, Galileo’s claim stands, as he was the one to both see and then write down the discovery collectively in a shorter space of time. And again, although Marius was c­ ertainly the first to publish tables concerning the moons of Jupiter, Galileo is generally credited with the discovery. In conclusion, it all centers on the publication of their respective books. Marius published his work on Jupiter in a book entitled Mundus Iovialis anno M. DC. IX Detectus Ope Perspicilli Belgici (“The Jovian World, discovered in 1609 by means of the Dutch Telescope”) in 1614. In the book, he claimed that he had observed Jupiter’s moons beginning as early as late November 1609 and had begun recording his observations on December 29, 1609 (January 8 on the Gregorian calendar). Since Marius did not publish any observations, as Galileo had done in his Sidereus Nuncius (“Starry Messenger” or “Sidereal Messenger”), published on March 13, 1610, it is impossible to verify Marius’s claims. Therefore, and seemingly conclusive in nature, Galileo first observed Jupiter’s moons on January 7, 1610, on the Georgian calendar – December 28, 1609 on the Julian calendar – so Galileo did see and record the moons first.

Europe

111

The original book written by Abd al-Rahman al-Sufi did not survive, but a copy from around 1009 is preserved at the University of Oxford in England.

Europe Until the end of the sixteenth century, star charts only contained the 48 constellations put forth by Ptolemy. Then, in 1595, a Dutch navigator named Pieter Dirckszoon Keyser (1540–1596), who had joined the first Dutch expedition on board the Hollandia to the East Indies, added 12 new constellations in the southern skies, named in part after creatures such as the toucan, peacock, and phoenix, along with a rather strange-looking Chamaeleon. Keyser was chief navigator and head of the steersmen for the voyage, which left Texel, an island in the province of North Holland, on April 2, 1595, under the command of Cornelis de Houtman (1565–1599) – a Dutch explorer who is also remembered as being something of a spy, who worked against the Portuguese by bringing back to the Netherlands privileged nautical information during his stay in Portugal! Under the instructions of the man who trained Keyser in mathematics and astronomy, Dutch-Flemish astronomer and cartographer Petrus Plancius (1552–1622), Keyser was asked to make observations to fill in the blank area of the sky around the south celestial pole on the European maps of the southern sky. Sadly, Keyser was to die in 1596, in an expedition that saw many casualties, but the catalog of 135 stars, probably measured with the assistance of Houtman, was delivered to Plancius. These stars appear as 12 new southern constellations on a 14-inch globe designed by Plancius in late 1597 or early 1598, produced in collaboration with the Amsterdam Flemish engraver and cartographer, Jodocus Hondius the Elder (1563–1612). The globe is the first surviving source that plots the locations of the newly discovered constellations with reasonable accuracy. In 1612 (or 1613), Plancius was to add eight further constellations on a 10-inch celestial globe published in Amsterdam by Dutch engraver, publisher, and globe maker Pieter van der Keere (1571-c.1646), although only two of these constellations survived and are still found on modern charts. The southern constellations were also depicted in 1603 on the globe of Willem Janszoon Blaeu (1571–1638) and on a single plate in the star atlas Uranometria published by Johann Bayer (1572–1625).

112

7.  Mapping the Sky, From Shi Shen to Charles Messier

German lawyer and celestial cartographer Johann Bayer produced his star atlas entitled Uranometria Omnium Asterismorum (“Uranometry of all the asterisms”) in 1603 (“uranography” meaning celestial or star cartography). The atlas was the first of its kind and is considered to be the first serious star atlas, with a plate for each of the 48 traditional figures. Much of the data referenced in the book is based on the work of Tycho Brahe. There is also a possibility that Bayer may have borrowed further work from that produced in 1540 by Italian astronomer Alessandro Piccolomini (1508–1579), his star atlas entitled Sfera del mondo e Delle stelle fisse (“The sphere of the world and the fixed stars”), although in addition to the stars in that catalog, Bayer did add an additional 1000 stars in a new system, which has become known as the Bayer designation. The Bayer designation identifies a star by a Greek or Latin letter followed by the genitive form of its parent constellation’s Latin name. Bayer used Greek letters for the brighter stars, but the Greek alphabet has only 24 letters, while a single constellation may contain 50 or more stars visible to the naked eye. When Bayer had run out of Greek letters, he continued with Latin letters. His original list of designations contained 1564 stars. Piccolomini’s contribution to astronomy is worth noting. His atlas is the first book of printed star charts, which also introduced a lettering system for the stars. Although the book is frequently reprinted, application of its nomenclature did not spread. Along with artist Alexander Mair (c.1562–1617), Bayer’s Uranometria really is a work of great substance. The atlas contains 51 copper plates engraved with the constellations. Indeed, the full translated title of Uranometria translates as “Uranometria, containing charts of all the constellations, drawn by a new method, engraved on copperplates.” Mair’s intricate constellation engravings were considered ground-breaking, and with Bayer’s cataloging and classification, the atlas was widely accepted and acknowledged, and not just by the scientific community. The atlas created a new precedence for the star atlas, moving away from the verbal descriptions that previous catalogs had used, entering a different, more engaging era. The beautifully crafted depiction of the constellations is shown on separate copper plates, carefully engraved on a grid with margins calibrated for each degree, allowing star positions to be read a fraction of a degree from the margins using a straight edge. Bayer also recorded rough fractions of the Milky Way, shown as a speckled, wavy column, in itself a unique characteristic of an

Europe

113

early star atlas and an art form subsequent atlas makers acknowledge in their own depiction of our galaxy. There are 31 plates that show parts of the Milky Way, with some scientists still striving to understand where Bayer obtained this data from. A name synonymous with the star catalog is that of French astronomer Charles Messier (1730–1817). Messier, a keen comet hunter, introduced the catalog to help fellow observers distinguish between other astronomical phenomenon that could be mistaken for comets while scouring the night sky. His comet hunting fascination may have stemmed from a young age when, at 13 years old, he observed a six-tailed comet. It was also documented that Catherine the Great (1729–1796), then Sophia, also observed the comet as a young girl as she was traveling to Russia to be wed! The comet that both Messier and Sophia sighted was to be labeled the Great Comet of 1744, also known as Comet Cheseaux, or Comet Klinkenberg-Cheseaux. The comet was discovered independently by Jan de Munck on November 29, 1743, at Middelburg, then on December 9, 1743, from Haarlem by Dutch mathematician amateur astronomer Dirk Klinkenberg (1709–1799), and 4 days later by astronomer Jean-Philippe Loys de Cheseaux (1718–1751). The comet became visible for several months during 1744, making for a dramatic sight in the night sky. Cheseaux, working at the observatory in Lausanne, said it lacked a tail and resembled a nebulous star of the third magnitude. The comet, though, steadily brightened as it approached perihelion, and by February 18, 1744, it had reportedly matched the brightness of Venus (with an apparent magnitude of −4.6), and by this time displayed a double tail. After it reached perihelion on March 1, 1744, the comet had become bright enough to be observed with the naked eye, when it caught the imagination of the young Messier. As it moved away from perihelion, a spectacular tail developed, extending well above the horizon while the comet’s head remained invisible due to the morning twilight. In the early part of March 1744, Cheseaux and other astronomers reported that the comet was displaying a rather unusual phenomenon, that of a ‘fan’ of six separate tails above the horizon, the tails possibly the result of three active sources on the cometary nucleus, exposed in turn to solar radiation as the nucleus rotated. Cheseaux is credited with being the last known observer in the northern hemisphere to see the comet, but as it traveled down to the southern hemisphere, its presence there was to cause as much of a stir, with reports that the tail length had grown to approximately 90 degrees by March 18, 1744. The comet was to disappear

114

7.  Mapping the Sky, From Shi Shen to Charles Messier

just over a month later on April 22, 1744. Messier’s interest was further stimulated by an annular solar eclipse, which he observed on July 25, 1748. Employed by the astronomer Joseph-Nicolas Delisle (1688– 1768), who was attached to the French navy, Delisle instructed Messier to keep careful records of the observations that he made, the first of which was that of the Mercury transit of May 6, 1753. Delisle himself had entered into the sphere of astronomy under the supervision of Jacques Cassini (1677–1756), son of Giovanni Cassini. During his career in astronomy, he also met with Sir Edmond Halley (1656–1742), in London. Messier’s love of comet hunting would bear fruit over the years, discovering 13 comets between 1760 and 1785. Near to the end of his life, Messier self-published a booklet linking the Great Comet of 1769 to the birth of Napoleon, who was in power at the time of publishing. Because of its outstanding brightness that led to it becoming a naked eye apparition, this, too, like the one sighted in his childhood, was given the label “great.” Messier had sighted the comet from the Naval Observatory in Paris. Late in the evening of August 8, 1769, in one of his routine sweeps with a telescope hoping to find a comet, Messier noticed a small nebulosity just above the horizon in the constellation of Aries. On the next evening he was able to sight the nebulosity with his unassisted eye, confirming the nebulosity to be that of a comet. By August 15, 1769, the estimated length of the comet’s tail spanned six degrees. Italian-born astronomer Giovanni Domenico Maraldi (1709–1788), nephew of Giacomo Filippo Maraldi (1665–1729), and Cesar Francois Cassini de Thury (1714–1784), second son of Jacques Cassini and Suzanne Francoise Charpentier de Charmois, saw the comet by telescope for the first time on August 22, 1769, and later by unaided eye. It is interesting to note some other astronomical activity carried out by the families mentioned, Maraldi and Cassini. Giacomo Filippo Maraldi himself, from 1700 to 1718, worked on a catalog of fixed stars, and from 1672 to 1719 made extensive studies of Mars, concluding that the ice caps on Mars are not exactly on the rotational poles of the body. He is also responsible for recognizing, in May 1724, that the corona visible during a solar eclipse belongs to the Sun and not the Moon, as many astronomers had believed. Among a list of discoveries is his observation of what is usually referred to as Poisson’s spot, an observation unrecognized until its rediscovery in the early nineteenth century by French

Europe

115

mathematician and astronomer Dominique Arago (1786–1853). Also known as the Arago spot or the Fresnel bright spot, the spot referred to is a bright point that appears at the center of a circular object’s shadow due to Fresnel diffraction (Fresnal after the optical pioneering work of Augustin-Jean Fresnal). The location, understanding, and definition of the spot were instrumental in the discovery of the wave nature of light and is a common way to demonstrate that light behaves as a wave. Fresnal had presented his work on diffraction as an entry to a competition on the subject sponsored by the French Academy of Sciences in 1819. The committee of judges included a number of prominent advocates of Newton’s corpuscular model of light, one of whom was French mathematician Simeon-Denis Poisson (1781–1840), who (as well as eventually lending his name to the ‘spot’) pointed out during his assessment of Fresnal’s presentation that the model Fresnal had presented predicted a seemingly absurd result. If a parallel beam of light falls on a small spherical obstacle, there will be a bright spot at the center of the circular shadow – a spot nearly as bright as if the obstacle were not there at all. An experiment was subsequently performed by Arago, and the spot (which was at this point to gain its alternative title of ‘Poisson’s spot’), was seen vindicating Fresnel, who won the competition! Giacomo Fillipo Maraldi was the uncle of Jean-Dominique Maraldi (1709–1788), who, while observing Comet De Cheseaux with Jacques Cassini (1677–1756), discovered two nebulous stars that later turned out to be the globular clusters Messier 15 and Messier 2. M15, at a distance of 33,600 light years, is situated in the constellation of Pegasus and is one of the oldest known globular clusters, with an estimated age of 12  billion years. M2, at a distance of 55,000 light years, is situated in the constellation of Aquarius and is one of the largest globular clusters known, with an estimated age of 13 billion years. Cesar-Francois Cassini de Thury was the second son of Jacques Cassini, who was son of Giovanni Domenico Cassini. Jacques Cassini succeeded his father to the official position at the Paris Observatory in 1712, later publishing, among other works, the first tables of the satellites of Saturn in 1716. Cesar-Francois, grandson of Giovanni, succeeded to his father’s official position at the observatory in 1756. Cesar-Francois, father of Jean-Dominique comte de Cassini (1748–1845), succeeded to his father’s position at the observatory in 1784!

116

7.  Mapping the Sky, From Shi Shen to Charles Messier

Along with his comet discoveries, Messier also discovered 40 nebulae, but it was the search for comets that was the real passion behind his star catalog. In 1757, Messier had begun hunting for a comet whose return was predicted by Sir Edmund Halley. However, a mistake in the calculations of his employer at the time led to the unfortunate Messier searching in the wrong patch of sky. On August 28, 1758, Messier discovered a fuzzy patch in the constellation of Taurus. Keen to establish the nature of the patch, Messier made repeated observations, but despite returning to the region night after night, the patch did not move in relation to the background stars, thus ruling out a comet. The nebula that had caught his attention was to become the first entry in his catalog, Messier 1, or M1, also known as the Crab Nebula. Messier’s great catalog, which still has much influence in modern-day astronomy, had been started. Messier, still working under the premise to identify and catalog non-cometary objects, next documented M2, a nebula previously discovered by Jean-Dominique Maraldi in 1746. M2, under very good skies, can be sighted with the naked eye, and is part of the Gaia Sausage, the hypothesized remains of a merged dwarf galaxy in Aquarius. The Gaia Sausage, also known as the Gaia-­Enceladus-­ Sausage or “Sausage Galaxy,” is thought to have merged with our own Milky Way some 8–11 billion years ago. It is one of the subject areas of study by the ESA spacecraft Gaia, originally the acronym for Global Astrometric Interferometer for Astrophysics, the initial name of the mission. Launched on December 19, 2013, the craft will also sweep the heavens for Jupiter-sized exoplanets. Messier’s application to the search yielded 38 objects for his catalog in a seven-month period in 1764, recording a further nine new nebulae in 1 day on March 18, 1781. Messier’s scope for inclusion in his catalog began to encompass the work of other astronomers, with the total number rising to 103 nebulae, 40 of which had been discovered by himself. Even after Messier had passed, objects known to have been discovered by him were later added to the catalog, seven more being added to his work in the twentieth century, with the final entry, M110, added in 1967. Messier had depicted M110 on a drawing of M31, first observing M110 on August 10, 1773. Interestingly, German astronomer Caroline Lucretia Herschel (1750–1848) discovered M110 independently on August 27, 1783, adding it to her own catalog at No.9. M110, also known as the Edward Young Star, is a dwarf elliptical galaxy in Andromeda. M110 is estimated to contain 10 billion stars and was the subject in August 1999 of a nova.

Europe

117

Caroline Lucretia Herschel made significant contributions to astronomy during her career, including finding several comets. The younger sister of William Herschel, Caroline was the first woman to receive a salary as a scientist, and the first woman in England to hold a government position. Her passion for astronomy started at a young age as a pastime, a hobby to keep her busy at night. Caroline found herself being constantly called upon by her brother William to assist in his own astronomical pursuits, giving great support to his passionate work on high-performance telescopes. However, Caroline found herself being drawn deeper into astronomy, now finding herself organizing William’s astronomical observations and making copies of astronomical catalogs that her brother had borrowed. Caroline continued to assist William further, being beside her brother as he compiled his own star atlas, to “sweep” the skies for other interesting objects. Caroline dutifully did as she was asked to do with the tasks asked of her, shifting from being something of a chore to more of an interest, reigniting that early pastime she had adopted as a child for observing the heavens. On August 28, 1782, Caroline commenced work on her first record book, and less than a year later, on February 26, 1783, she made her first discovery that was not included in Charles Messier’s catalog. On that very night, Caroline observed M110, independently discovering the second companion of the Andromeda galaxy and adding her own prefix to it. William sensed that Caroline had opened up a new avenue of observing that he, too, could perhaps become involved in, sensing that there were a great number of discoveries to be made. However, William, having relegated his own sister to taking measurements of double-stars, soon realized Caroline’s true qualities, not only as a record keeper but in time as an observer in her own right. With the use of John Flamsteed’s (1646–1719) star atlas, William would use star positions on the atlas as reference points for the nebulae discoveries, all of which was documented by Caroline who, in turn, finding Flamsteed’s method of organizing the sky by constellation not as useful as it could be, organized her own catalog. Flamsteed, the first Astronomer Royal, had been honored for his preparatory work on Stellarium Inerrantium Catalogus Britannicus (“British Catalogue of Fixed Stars), a 3000-star catalog, and a star atlas called Atlas Coelestis, both of which were published posthumously. The Stellarium Inerrantium Catalogus Britannicus is considered one of the most influential star catalogs in the history of astronomy and the most accurate of its time.

118

7.  Mapping the Sky, From Shi Shen to Charles Messier

It groups stars in 55 constellations: 46 of the 48 Ptolemaic constellations; constellations that extend too far south are only partially covered, with the addition of nine newer constellations that Flamsteed attributes to Hevelius, although the details of the attribution are quite complex. Flamsteed also assigned to the stars a system entitled Flamsteed numbers, whereby numbers were tagged to stars by constellation, a technique used in modern day atlases that has its founding in the Flamsteed’s work. Whereas these numbers do not appear explicitly in the official version of the catalogue, they do appear in a version of the atlas published by French astronomer Joseph Jerome Lefrancois de Lalande (1732–1807). At the eyepiece of William’s newly built telescope, Caroline was to discover eight comets, the first of which was on August 1, 1786, also in 1795 rediscovering Comet Encke. In 1797, William’s own observations of the heavens had shown that there were a great many discrepancies in John Flamsteed’s catalog, turning once again to Caroline to produce, some 20  months later, the Catalogue of Nebulae and Clusters of Stars (CN), published by the Royal Society in 1798. This catalog was later expanded into the General Catalogue of Nebulae and Clusters of Stars (GC) by William’s son, John Frederick William Herschel (1792–1871). The “CN” and the “GC” being the precursors to British astronomer John Louis Emil Dreyer’s (1852–1926) New General Catalogue (NGC), used by astronomers for modern day observations. For reference, Dreyer was also to write a biography on Tycho Brahe. The NGC is a catalog of deep sky objects, borne out the work of the Herschels, with 7480 objects contained within it, all with the tag NGC.  It remains one of the largest and most comprehensive catalogs containing all types of deep space phenomena, including galaxies, star clusters, and nebulae. Alongside this work, Dreyer published two supplements to complement the main catalog. These Index Catalogues were published in 1895 and 1908, respectively, with the first part, IC I, containing 1520 objects and the second, IC II, containing 3866 objects. A total of 5386 objects were therefore included across the two volumes, all of which were collectively referred to as IC objects. Errors in the catalogs, with a list of corrections to the IC published in 1912. In 1886, Dreyer, who had already published a supplement to Herschel’s GC catalog, which contained around 1000 objects, was asked by the Royal Astronomical Society to compile a completely new version of the NGC.  This was a tall order that saw Dreyer having to deal with conflicting data that had been collected by

Europe

119

many astronomers using greatly differing telescopic powers. The task meant Dreyer had to check much of the observed data for himself, but with such a mammoth undertaking, he was forced to accept a proportion of the published work as accurate for the sake of the new NGC. Understandably, there were errors, mostly relating to positional data and descriptions, but Dreyer referenced the catalog, which allowed later astronomers to review the original references and publish corrections to the original NGC. Czech astronomer Antonin Becvar (1901–1965) made a significant contribution with his Atlas Coeli Skalnate Ples (“The ­Skalnate Pleso Atlas of the Heavens”) in 1951. His work, published by the Sky Publishing Corporation, was a state-of-the-art atlas, the kind of which had not been produced before. The atlas contained a set of 16 celestial charts covering the entire sky. Named after the Skalnate Pleso Observatory (Skalnate Pleso translating as “Rocky Tarn”), perched at an altitude of 1786 m in the Tatra Mountains of Slovakia, the charts are hand-drawn by Antonin Becvar, who coincidentally founded the observatory. Also referred to as the Atlas Coeli 1950.0, the work at the time of publishing was somewhat unique, as it contained essentially all non-stellar objects that were visible with an 8-inch telescope. Much of the work on the atlas was carried out by a volunteer group of students at the observatory. The final plotting of the Atlas, which was hand-drawn, was the work of Bevcar. It was fitting that so many amateur astronomers were involved, as the original idea came from Czechoslovakian amateur astronomer Josef Klepesta (1895–1976). Until the atlas went out of print in the 1970s it remained an extremely popular work with both amateur and professional astronomers. Clinically presented with a wealth of data, Atlas Coeli 1950.0 strongly influenced many atlases that followed. The work of Dutch celestial cartographer Wil Tirion (b. 1943) conveys that influence, with his most famous work Sky Atlas 2000.0, greatly admired for its accuracy and sheer lavish quality. The NGC was superseded by the Revised New Catalogue of Nonstellar Astronomical Objects (RNGC) in the early 1970s, fixing some mistakes but also introducing some new errors. Nearly 800 objects are listed as “non-existent” in the RNGC. A further revision was introduced titled the NGC 2000.0 (also known as the Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters), which contains a 1988 compilation of NGC and IC references. Within the publication, as with its predecessors, there are corrections! A Revised New General Catalogue and Index Catalogue (RGNC/IC) was introduced in 2009.

120

7.  Mapping the Sky, From Shi Shen to Charles Messier

Digital Age From cuneiform tablets to seafaring notes scrawled on parchment, to copper plates and lavish star atlases, the transition has been remarkable but ultimately necessary as though the tableau of the night sky in essence doesn’t change greatly, the means and method used to capture the heavens certainly does – in turn, reflecting a progressive humankind and the advance in technology. The learning curve will continue as the boundaries are pushed back through cumulative knowledge gained by advances in the ever-changing world of science and technology. The yearning to discover more is a driving force, and humankind can reap the benefit of the work of astronomers who dedicate their lives to furthering our understanding of the universe in which we live. The digital age and the eras that follow, while perhaps more complex, more intricate, and more elaborate, may well be able to capture new sights and sounds of the universe that were once thought to be impossible to do, but in no way do they make less significant the work of our ancestors who recorded the skies.

8. The 1639 Transit of Venus Earth’s Sister World The recording of astronomical phenomena can take on many guises, not just those that are immediately apparent. The simple exchange of handwritten letters with ideas and thoughts between one astronomer and another can serve as the basis to many a discovery, for without such communication and the subsequent archiving of such works, many an untold story would have been lost in history, often to be abridged with speculation and conjecture (Fig. 8.1). One such case surrounds the 1639 transit of Venus. As British astronomy made advances throughout the centuries, the observations of the transit made by two astronomers in particular made for a shift from the era of classical astronomy, whose cornerstones were documentation and tabulation, to the modern era, which included, as its backbone, observation, prediction, and comprehension. The importance of such communication should not be underestimated, for intertwined in personal correspondence, which would become national treasures of scientific note, one is afforded a very intimate insight into the author behind the hard science, discovering the very nature of the passion that drives people to succeed, and how through years of dedication, commitment, and a determination to see a task through to fruition, the learned person springs forth to deliver what for some is the end result of a life’s work. No greater insight can be afforded via communication before the advent of typed then keyboard text than the simple communication by letter. The two astronomers in question were Jeremiah Horrocks (1618–1641) and William Crabtree (1610–1644). Horrocks was an English astronomer, the first person to demonstrate that the Moon moved around Earth in an elliptical orbit. Born in Liverpool, Lancashire, Horrocks also posited that comets followed elliptical orbits. He supported his theories by analogy to the motions of the conical pendulum, noting that the plumb bob was drawn back © Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_8

121

122

8.  The 1639 Transit of Venus

Fig. 8.1. Transit of venus, June 5/6, 2012. Solar Dynamics Observatory. (Courtesy of NASA.)

and released as it followed an elliptical path, and that its major axis rotated in the direction of revolution as did the apsides of the Moon’s orbit. The term apsides refers to an extreme point in the orbit of an object, from the Greek word apsis, meaning “orbit.” William Crabtree was an astronomer and mathematician from Broughton in Salford, and his own work centered on the collaboration with Horrocks with regard to the transit of Venus. The two, each working separately but working as friends and colleagues and corresponding by letter, were to make the first known observations of such a transit – Horrocks from the village of Much Hoole in Lancashire, Crabtree from his home in Broughton. Horrocks’ work was acknowledged by Sir Isaac Newton (1642–1726/27), the English mathematician, physicist, and astronomer, described in his own day as a “natural philosopher” and still regarded as one of the most influential scientists of all time. Horrocks anticipated Newton in suggesting that the Sun as well as Earth had influence on the Moon’s orbit. As part of Newton’s Principia, first published on July 5, 1687, a work in three books that contains his laws of motion and of universal gravitation, Newton acknowledged Horrocks’ work in relation to his theory of lunar motion. Horrocks became fascinated by the so-called “new” astronomy of Galileo Galilei and others, amassing a great number of books, including a copy of Dutch astronomer and mathematician

Earth’s Sister World

123

Philip Lansberg’s Tabulae Motuum coelestium perpetuae, bearing his Latin autograph, which survives to this day on view in Trinity College Library, Cambridge, England. Also in his collection were four titles by Johannes Kepler, who greatly motivated Horrocks, instilling within him a passion to make his own independent advances on Kepler’s work. Horrocks, besides the perhaps overshadowing link with the transit of Venus in 1639, was the first person to demonstrate that the Moon moved around Earth in an elliptical orbit, also positing that comets follow elliptical orbits. This “lunar theory” had perplexed many astronomers, unable to answer with certainty the reason why there are small variations (or perturbations) in the Moon’s motion. The theory has a history of speculation spanning 2000  years, taxing mathematicians and astronomers at the forefront of their careers to not just theorize but to actually demonstrate, something Horrocks was eventually able to do. Only 30 years before, in 1609–10, it had been Galileo’s ingenious application of the newly invented “Dutch spyglass,” turning said telescope to the heavens, which had ushered in a revolution in astronomy. The newly magnified universe was an eternity away from the classical naked-eye observations of the Greeks, with the Moon transformed from an apparent smooth, silvery ball into a rough and mountainous world, far detached from all that was previously considered of Earth’s satellite. Sunspots also dispensed with the interpretation of the Sun being perfect and changeless, for now darkened areas revealed themselves, and the classical status of the Sun was forever altered. Jupiter revealed a disc to behold, with accompaniment in the form of four moons orbiting around it. Venus revealed phases and that it was clearly rotating around the Sun. Despite not proving that Earth orbited the Sun, Galileo had used this catalog of revealing finds to argue for a Copernican heliocentric model, directly at odds with the geocentric universe proposed by Aristotle and Ptolemy. Coupled with Tycho Brahe’s positional observations of the planets, and Johannes Kepler’s mathematical analyses of planetary motion, the evidence placed the Copernican theory in a much more favorable position than that of the classical geocentric theory. Other correspondence between Horrocks and Crabtree demonstrated a familiarity with the works of European contemporaries such as Pierre Gassendi (1592–1655), William Gilbert (1544–1603), Rene Descartes (1596–1650), and navigational writer Edward Wright (1561–1615).

124

8.  The 1639 Transit of Venus

In 1631, French mathematician and astronomer Gassendi observed the transit of Mercury across the Sun that Kepler had ­predicted. Gassendi also made a measurement to about 25% accuracy of the speed of sound, showing it is invariant in pitch. He also conducted work on determining longitude via eclipses of the Moon. English physician (to the court of Elizabeth I) and physicist William Gilbert is credited by many as the “father of electricity and magnetism.” In 1600, Gilbert published De Magnate, which set out to distinguish the difference between magnetism and static. His work, which was quickly accepted as the standard work on electrical and magnetic phenomena throughout Europe, compared the magnet’s polarity to the polarity of Earth, developing an entire magnetic philosophy on this analogy. His findings suggested that magnetism was the soul of Earth and that a perfectly spherical lodestone (a naturally magnetized piece of the mineral magnetite), when aligned with Earth’s poles, would spin on its axis, just as Earth spins on its own axis over a period of 24 h. De Magnate was in fact calling the traditional cosmologists’ belief that Earth was fixed at the center of the universe into question, indeed outright debunking the claim. Galileo was to concern himself with the proposal, eventually arriving at the proposition that Earth revolves around the Sun. French philosopher and scientist Rene Descartes is credited with being the father of analytical geometry, the so-called bridge that spans algebra and geometry. Analytical geometry is widely used in physics, engineering, and also in aviation, rocketry, space science, and spaceflight. His Meditations on First Philosophy (1641) remains standard text in most university philosophy departments. Descartes is known for his influential arguments for substance dualism, where mind and body are considered to have distinct essences, one being characterized by thought, the other by spatial extension. His best-known philosophical quote is “I think, therefore I am.” English mathematician and cartographer Edward Wright was noted for his book Certaine Errors in Navigation (1599; 2nd edition 1610), which for the first time explained the mathematical basis of the Mercator projection, a cylindrical map projection presented by Flemish geographer and cartographer Gerardus Mercator (1512–1594) in 1569. This world map was based on a new projection that represented sailing courses of constant bearing (rhumb lines or loxodrome) as straight lines – an innovation

Revising Kepler’s Rudolphine Tables

125

that is still employed to this day in nautical charts. In navigation, a rhumb line is an arc crossing all meridians of longitude at the same angle, that is, a path with constant bearing as measured relative to true or magnetic north. Wright’s reference tables derived from his mathematical study and were seen as the essential step necessary to make practical both the making and navigational use of Mercator charts.

Revising Kepler’s Rudolphine Tables Crabtree shared the admiration that Horrocks had for the work of Kepler. Their belief and enthusiasm in Kepler’s work spawned a group of astronomers, calling themselves “Nos Keplan,” that was to form in the north of England; these were considered the first people to gain a realistic notion of the size of the Solar System. Aside from Horrocks and Crabtree, there was English astronomer and mathematician William Gascoigne (1612–1644). Gascoigne was the maker of scientific instruments, including the micrometer, sometimes referred to as the micrometer screw gauge, a device incorporating a calibrated screw widely used for accurate measurement of components. Micrometers are used in telescopes or microscopes to measure the apparent diameter of celestial bodies and microscopic objects. Kepler conducted many experiments in the field of optics, producing an improved version of the refracting telescope, the Keplerian telescope. In the late 1630s, Gascoigne was working on a Keplerian optical arrangement when a thread from a spider’s web happened to become caught at exactly the combined optical focal points of two lenses he was working with. When he looked through the arrangement, Gascoigne saw the web bright and sharp within the field of view. Gascoigne realized that he could more accurately point the telescope using the line as a guide, this genius insight leading him to invent the telescopic sight by placing crossed wires at the focal point to define the center of the field of view. Known as a reticle, or reticule (from the Latin reticulum, meaning “net”), the sighting device was to also find applications in microscopes, and the screen of an oscilloscope. There seems to be some conflict as to who exactly made the discovery of the reticle, sometimes referred to as the graticule (from the Latin craticula, meaning “gridiron”), with both Gascoigne and

126

8.  The 1639 Transit of Venus

English architect Robert Hooke (1635–1703) mentioned. However, Gascoigne’s claim pre-dates that of Hooke. Gascoigne added the new-found arrangement to a sextant modeled on the instrument used by Tycho Brahe, although Tycho’s sextant was only a naked-eye instrument. In his time, Tycho had devoted much time to improving the accuracy of the sextant and the quadrant  – the sextant being a doubly reflecting instrument that measures the angular distance between two visible objects, and the quadrant being an instrument that is used to measure angles up to 90 degrees. Gascoigne, whose own sextant was approximately 1.5  m in radius, had already measured the distance between astronomical bodies to a high degree of accuracy. He realized that by introducing two points, whose separation could be adjusted using a screw, he could measure the size of the image enclosed by them. Using the known pitch of the screw, and knowing the focal length of lens producing the image, Gascoigne was able to calculate the size of the object, such as the Moon or the planets, to a hitherto unattainable degree of accuracy. Crabtree was so taken with the instruments following a visit to Gascoigne’s home that, upon his return to Lancashire, he immediately set about writing of his encounters to Horrocks, with a further piece of correspondence to Gascoigne himself, asking if he might obtain such instruments. The exchange of communication between the three is of great importance to astronomy, as it records the very development of the instrument that in turn would, via English astronomer Richard Towneley (1629–1707), a nephew of Gascoigne’s friend Christopher Towneley, be introduced to Robert Hooke, who used the invention to calculate the size of comets and other celestial bodies. The micrometer, as it became known, was to lie at the heart of astronomical measurement for many years to follow! Although it is only speculated as to how Horrocks and Crabtree actually met (some historians questioning if they actually met at all), both were self-taught in the field of mathematics, and they worked religiously to improve Kepler’s Rudolphine Tables, named after Rudolf II, Holy Roman Emperor (1552–1612). Their research to improve the tables was widely shared, with one of their own contemporaries, Gassendi, actively involved at the time in his own quest to update them. These tables consisted of a star catalog and planetary tables, published by Kepler in 1627, using observational work including

Revising Kepler’s Rudolphine Tables

127

some that had been collected by Danish astronomer Tycho Brahe. Brahe’s own observations were regarded as the best available and some five times more accurate than any other data at the time. Until the end of the sixteenth century, the most widely used had been the Alphonsine tables, first produced in the thirteenth century and regularly updated thereafter. Although not very accurate at all, there was little else available at the time so their usage continued with additional data incorporated over the years that followed. The Alphonsine tables, named after Alfonso X of Castile (1221–1284), who sponsored their creation, provided basic data for computing the position of the Sun, Moon, and planets, relative to the fixed stars, stars that appear to not move relative to each other in the night sky compared to the foreground of Solar System objects that do. Compiled in Toledo, Spain, the tables start on January 1, 1252, the date of the coronation of Alfonso X. The Prutenic tables (Prutenia meaning “Prussia”) were published by German astronomer and mathematician Erasmus Reinhold (1511–1553) in 1551. This new set of astronomical tables were based on the work of mathematician and astronomer Nicolaus Copernicus’ De revolutionibus orbium coelestium (“On the Revolutions of the Celestial Spheres”), the epochal exposition of Copernican heliocentrism published in 1543. This publication, just before his death, was to trigger a major event in the history of science, with the Copernican Revolution dramatically shifting away from the Ptolemaic model of the heavens, which described the cosmos as having Earth permanently positioned at the center of the universe, to Copernicus’ heliocentric model, with the Sun at the center of the Solar System. The Ptolemaic system had been developed by Greco-Roman mathematician and astronomer Claudius Ptolemaeus in the second century a. d. Ptolemy’s Almagest, considered one of the most influential scientific texts of all time, is the only surviving comprehensive ancient treatise on astronomy, charting the apparent motions of the stars and planetary paths. Ptolemy’s view held sway with the science community for more than 1200 years before the Copernican Revolution. During their efforts to update and improve Kepler’s Rudolphine tables, the pair, who continued to exchange ideas by correspondence, encountered a similar problem, which baffled them both. Why were the principal astronomical tables then in use, even those based on the observations of Tycho Brahe, so often defective when it came to making exact predictions of astronomical events

128

8.  The 1639 Transit of Venus

such as eclipses, conjunctions, or lunar occultations? Ironically, there was particular scorn poured on Philip Lansberg’s Tabulae Motuum coelestium perpetuae, with Lansberg later accused of leading Horrocks and Crabtree astray because of the errors in the tables. One of the reasons behind the errors in the work was in part due to the fact that Lansberg did not accept Kepler’s discovery of elliptical orbits.

Observation of the Transit Practical experience had taught both Horrocks and Crabtree that cosmological truths were not to be found in the tabular computations, but only in the direct observation of the heavens where they could apply measurements firsthand, rather than rely on the invariably indifferent tables of the time. It is considered, by some of the remarks that Crabtree made, that he had the foresight to see this eventuality long before Horrocks, making the realization that this was going to be the premise for any advancement, drawing Horrocks away from a routine that he had apparently fallen into – that of relying on computation work rather than the ‘new’ approach, which was eventually to inspire them to their combined greatest achievement. Horrocks was well versed in the work on planetary transits by Kepler and Gassendi. A month previously, in October 1639, Horrocks came to the realization that Kepler’s statement, that after the 1631 transit there would not be another transit of Venus until 1761, was wrong. From his own calculations, Horrocks deduced that transits of Venus occur not singly but in pairs 8 years apart. He predicted that as Venus came to inferior conjunction on November 24 it would pass directly in front of the solar disk. Horrocks, who was known as an assiduous and careful observer, anxious to extend the limits of precision and to seek out and eliminate sources of possible observational error, was convinced that a measurement could be made of the apparent diameter of Venus to within a fraction of a second of an arc when it was seen as a dull black disk on the face of the Sun, compared to an accuracy of around1 min of arc when seen in its normal position as the bright morning “star” close to the Sun. Several weeks before the transit, Horrocks made positional observations of Venus as a morning “star” in readiness for event, eager to have covered as many scientific aspects as possible in preparation.

Observation of the Transit

129

By telling Crabtree and others (with unfortunately only Crabtree taking any notice before the event), Horrocks had hoped to encourage others to observe so that even if the skies were cloudy for some, a break may be afforded for others, giving the collective number of people involved the best possible chance of the event being observed and documented. Among those Horrocks attempted to contact were Samuel Foster (died 1652), Professor of Astronomy at Gresham College, London, but to no avail. Correspondence was also sent to his younger brother Jonas, living back at the family home in Toxteth, Liverpool, but again without luck. On the eve of the event, Horrocks was concerned that the weather would be unfavorable for the transit, as he believed that a rare planetary conjunction would produce severe weather. Despite his clear anxiety over the weather conditions, a concern with which many astronomers can relate, Horrocks was meticulous in his preparation. On November 23, 1639, from his location in Much Hoole, Horrocks arranged the image projected from his telescope (which had cost half-a-crown) onto a sheet of white paper, having a circle 6 inches in diameter traced upon it, the circumference being divided into degrees. Fearing his calculations could be incorrect, Horrocks deemed that he would start his observations a day before the transit just in case, with the calculated start for the event on November 24 at 3:00 p.m., still more than 24 h away. Horrocks also knew that as it was deep into autumn, daylight was short, and the opportunity an even shorter one before the Sun was to set. The transit occurred on November 24, 1639, on the Julian calendar (December 4 on the Gregorian calendar), the first transit ever to have been observed by human eyes. The transit, which lasted almost 6 h, commenced just before 3.15 p.m. on Sunday afternoon, and by the time that three successive positions of the planet upon the solar disk had been recorded, the Sun had set. Horrocks, then aged 20, observed from Much Hoole, while 29-year-old Crabtree also viewed the event, 30 miles away in Salford. At sunrise on Sunday November 24, an overcast sky greeted Horrocks, but with due patience, he first saw the tiny black shadow of Venus crossing the Sun at 3:15 p.m., observing for half an hour until sunset at 3:53 p.m. Crabtree, his friend and colleague, used a similar set-up to make his observations but had insufficient time to make any

130

8.  The 1639 Transit of Venus

measurements, as the cloudy skies across Broughton only afforded him a brief glimpse of the transit. The three observations that were made at the start of the transit – 3:15 p.m., then at 3:35 p.m., concluding at 3:45 p.m. – enabled Horrocks to derive the major celestial mechanics of the event, including Venus’ precise orbital velocity at inferior conjunction, the inclination of its orbital plane to that of the ecliptic, and the exact point of the node of that orbit in space in relation to the Sun’s center. It is quite remarkable that in just half an hour’s worth of observation so much information should be gleaned, given that the discoveries made by Galileo spanned several months during the winter of 1609–10. The task that followed the event was of as much importance as the transit itself, and that was to write up, record, and accurately document both his and Crabtree’s work for the scientific community. However, it must be noted that there were other conclusions drawn from the transit that in some respects overshadowed the findings that were to be so greatly admired by his contemporaries. The most notable of these other findings was in Horrocks’ opinion the apparent smallness of Venus when seen “eclipsing” the Sun, just as Gassendi had noted when he observed Mercury transiting the Sun. Horrocks was frankly amazed just how small Venus was. Indeed, instead of being three or more arcminutes across, as previous astronomers had presumed from the planet’s glare in the evening sky, during the transit, Venus returned a mere 1 min 12 sec of an arc. Horrocks noted that Crabtree’s observations had also pointed to how small Venus was during the transit, an estimated 7/200 of the total solar diameter, or a mere 1 min 3 sec of an arc. The finding so challenged Horrocks that he embarked on a series of post-transit laboratory experiments on the nature of optical brilliance, glare, and the human eye’s tendency to overestimate the size of brilliant objects against dark backgrounds, such as Venus shining against the dark sky. But in transit, Venus’s true form and size are revealed. And that form was circular, inky-black, and opaque, so that in Horrocks’ opinion Venus joined Mercury, Jupiter, and Saturn as a hard planetary body. Horrocks was to produce several drafts of a Latin treatise Venus in Sole Visa (“Venus seen on the Sun”), based on the work conducted by himself and Crabtree, which he presumably intended to publish. On January 3, 1641, as he was preparing to journey from Toxteth to visit Crabtree in Salford, Horrocks died. The causes of

Observation of the Transit

131

his death at the age of 22 are not known, but after his passing, there were many admirers waiting to take up the gauntlet, a new generation keen to push the boundaries further, building on the work of Jeremiah Horrocks. Some of the drafts of Venus in Sole Visa were kept by Crabtree, who died in July 1644, just 3 years after Horrocks’ passing. Their correspondent, William Gascoigne, died in the same year, pre-deceasing Crabtree by just a couple of days, killed at the Battle of Marston Moor during the English Civil War of 1642–46. Gascoigne, who served as an officer in the Royalist army, left no record of having seen the transit. Of his friend and astronomy colleague, Crabtree wrote on the back of a bundle of letters: “Mr. Jeremiah Horrocks’ letters to me for the years 1638, 1639, 1640 up to the day of his death, very suddenly, on the morning of 3 January; [1641]; the day before he had arranged to come to me. Thus God puts an end to all worldly affairs. I have lost, alas, my dear Horrocks. Hinc illae lachrimae [thus the tears fall]. Irreparable loss.” With the three deceased, it was left to others in the scientific community to gather as much evidence together of the documentation recorded by Horrocks and Crabtree, not just for science purposes but to uphold the honor of the men behind the discovery. Horrocks’ papers remained with his family for a short time, although some were destroyed in the Civil War. Some papers were taken to Ireland by his brother Jonas, but never seen again. Other surviving papers were passed to Christopher Towneley, where they were reviewed by astronomer Jeremy Shakerley (1626–1653), who wrote three books on astronomy published between 1649 and 1653. Shakerley spoke of Horrocks’ researches with the highest of praise, especially his discoveries concerning lunar theory. Among others attempting to preserve the work were English poet and translator Sir Edward Shereburn (1618–1702). By the 1660s, it was clear that the work of Horrocks and his colleagues were of significant importance. The surviving pieces of correspondence that had passed between Horrocks and Crabtree after 1636  – records of observations, Horrocks’ treatise on the lunar orbit, Gascoigne’s letters, and even drawings and actual parts of their instruments  – were gradually being brought to London. The Civil War appears to have destroyed a fair amount of the documentation, while even more documents were destroyed when the place where some of them were going to be published was burnt down in the Great Fire of London in 1666.

132

8.  The 1639 Transit of Venus

There remains much speculation about the material that went to Ireland with Horrocks’ brother, and the idea that though they are deemed lost, there is the possibility that the papers merely await rediscovery in some private Irish archive. History relates that Jonas was sent there as part of the Protestant “planting” of that country, and it is possible the records were stored for future reference. Enough manuscripts survived to enable John Wallis (1616– 1703), then Professor of Geometry at Oxford, with the assistance of Robert Hooke and others, to publish the works of Horrocks, with further material that came to light. Indeed, the works of Horrocks were to find their way into many publications. Horrocks’ lunar theory was first published in 1672. Tables constructed from this by the first Astronomer Royal John Flamsteed were included in the edition of the following year. From observations made in 1672 and 1673, Flamsteed concluded that the tables were better than any then in print, and Newton later proposed corrections, which further improved their accuracy. Tables based on Horrocks’ lunar theory continued in use up to the middle of the eighteenth century, when they were superseded by the works of Czech-­ German Catholic priest, astronomer, and teacher Christian Mayer (1719–1783). Of Horrocks’ work Venus in Sole Visa, manuscripts were published with copies in evidence from the 1640s and 1650s, although there seems to be no clue as to how one such copy made it into the hands of Polish astronomer Johannes Hevelius, the work traveling to the seaport of Danzig (Gdansk). In 1662, Hevelius issued an elegant Latin impress of the work from a private press at his great observatory in Danzig. In this, its first printed edition, Horrocks’ Venus in Sole Visa formed a companion piece to Hevelius’s own observations of the 1661 Mercury transit. From Hevelius’s work, it was clear that he was all too conscious of the significance of Horrocks’ achievement and was placing Horrocks alongside Galileo, Gassendi, and Kepler, at the forefront of European research into “new astronomy.” Such an accolade would surely have pleased Horrocks, to be placed alongside colleagues that he admired – and, in some respects, aspired to. Hevelius’ tribute to Horrocks chimed right across Europe, for Hevelius himself was held in high esteem; he was one of the greatest European “big telescope” astronomers, someone who commanded an audience. In 1641, Hevelius built an observatory on the roofs of his three connected houses, equipping it with splendid instruments that ultimately included a large Keplerian telescope

Observation of the Transit

133

of 46 m focal length, with a wood and wire tube that he constructed himself. It is thought that this telescope may have been the longest “tubed” telescope before the advent of the tubeless and aerial telescope. The aerial telescope is a type of very long focal length refracting telescope, built in the second half of the seventeenth century, and without the use of a tube. Instead, the objective was mounted on a pole, tree, tower, or building, or other structure on a swivel ball-joint. The inventor of this type of telescope is unclear, although it has been linked with Dutch physicist, mathematician, and astronomer Christiaan Huygens (1629–1695), and his brother Constantijn Huygens, Jr. (1628–1697). Following the publication in Latin of the correspondence between Horrocks and Crabtree in a work entitled Opera Posthuma, it wasn’t until 1859 that Horrocks’ magnum opus became available in English. In the same year, Arundel Blount Whatton published his translation of Horrocks’ Venus in Sole Visa  – The Transit of Venus, which Whatton prefaced with “A Memoir of this [Horrocks’] Life and Labours.” It remains quite remarkable that on that afternoon, as Horrocks and Crabtree snatched a glimpse of the transit of Venus, so much of what proceeded that day would have been lost if it were not for the correspondence between them and their colleagues in the simple format of handwriting. Preserved and cherished by those inside and outside the scientific community, it is a testimony to how one chapter in astronomy won’t be forgotten, and all because quill was placed to parchment.

9. Comets A Fiery Visitor One type of visitor in our skies has probably seen the most variety of documentation over the centuries: comets. Such spectacles seem to have aroused the basic instinct in humankind, firstly to be very cautious of them, then to understand and appreciate such wonders. One can barely argue with the feelings when such an apparition occurred in the night sky, out of the ordinary, puzzling, and by its own brilliance, something to behold and be fearful of. With the background stars an accepted norm, along with the phases of the Moon, and possibly a loose understanding with regard to the presence of Venus in the evening and morning sky, the appearance of a comet would throw the natural order into chaos, both provoking and commanding a respect probably unparalleled at the time. What could it be? Where did it come from? Does it mean something? All questions that went unanswered for many years but that did not prevent the many eyes that saw the comet from wanting to make some sort of record, mark, or documentation, to reference what had been sighted, and thereby, over time, building up an impressive catalog of how humankind embraced this celestial wanderer.

Early Records The first observations of comets originate from the third millennium b. c. In ancient cultures, their sudden appearances were considered to be signs from the gods, and because of the ‘imbalance’ it presented and the disturbed harmony it provoked in the heavens, observers soon deemed comets to be a bad omen. Such a reputation would be hard to overcome, with astronomers taking many centuries to calm the unrest when a comet appeared, attempting to offer a logical and rational explanation for their appearance. Understandably, many refused to listen and were too set in their ways to embrace any such colorful interpretation, but slowly, © Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_9

135

136

9. Comets

especially when it was proven that one would actually reappear, the gentle art of scientific persuasion won through. Nonetheless, whatever humans made of comets in ancient times, their fiery magnetism in the night sky could not fail to captivate, with archaeological records probably not giving true justice to just how long comets have been observed. As referenced in the first two chapters of this book, some archaeologists suggested that prehistoric rock paintings, found in several sites across the globe, might portray comets. Early rock carvings resembling comets have been found in Scotland dating back to the second millennium b. c., and a comet-like shape found on rock carvings in Val Camonica, Italy, dates back to the late Iron Age.

The Chaldeans The first systematic observations of the sky are credited to the Chaldeans, who lived in the ancient region of Babylon, or modern-­ day Iraq. During the third millennium b. c., around the time of the Bronze Age, the Chaldeans started practicing astronomy, recording their findings on clay tablets. The tablets are considerable in number, and while references to comets have only been found to date on these tablets, there are references to suggest, notably from Roman philosopher Seneca (4 b. c–a. d.65), that the Chaldeans had a long and keen interest in comets, which in turn could mean that further tablets are yet to be discovered. Given the length of time dedicated to observing the phenomenon, there is a strong likelihood that they would have developed ideas to explain exactly what they were documenting, rather than just blindly making a drawing and reference to them. Therefore, aside from the speculative interpretation of cave art, these tablets present themselves as a significant milestone in how recordings of such phenomenon were made at this juncture in history.

Chinese Astronomers Chinese astronomers had a great fascination for comets. Their records of comets are the most extensive and accurate in existence from the ancient and medieval periods, stretching back across three millennia. The dedication to detail is incredible, with records dating at least as far back as 613 b. c., and possibly for

Chinese Astronomers

137

many centuries before this. The Chinese made continuous records all the way through to the nineteenth century, using a meticulous eye for detail throughout, plus a consistently retained method of making such recordings. Comets were of particular interest, observed in great detail because of their astrological significance. Such is their accuracy of documentation that they allow the calculation of orbital elements, and modern astronomers have been able to achieve this for many comets, most notably that of Halley’s Comet, the orbit of which has been directly determined using Chinese records. Interestingly, these early records call comets beixing (“bushy star” or “sparkling star”), with later references making a further distinction between beixing and huixing (“broom star”), that is, comets without and with a tail. The earliest confirmed Chinese comet observation dates from 613 b. c., with a possible sighting of Halley’s Comet attributed to 1059 b. c., although there is some doubt if this was an actual sighting or merely a reference to the comet as a result of back calculation. Other such potential sightings of Halley’s Comet exist, but to which end have never been confirmed. A comet was recorded in ancient Greece in 467 b. c., more than likely being Halley’s Comet. Chinese chroniclers also mention a comet at this time, which would seem to corroborate the Greek reference. Although extremely likely that it was Halley’s Comet, there remains nothing to substantiate any claims. Sighted between 468 and 466 b. c., the Greek records that state the comet’s location, duration, and associated meteor shower all suggest it was Halley. The most ancient document known to exist on comets is the spectacular drawing, now called the Silk Atlas of Comets, found in a tomb from the Mawangdui site near Changsha, in the Hunan province in south China, 1973. The Atlas dates from around 185 b. c. and is now housed in the Hunan Provincial Museum. Upon it, a variety of comet formations, which demonstrate just how careful the observations were, are detailed. Different kinds of comet heads and tails are painted in the manuscript, showing that comet observation at this time was already very precise, done according to scientific classification. Collectively, the silks are referred to as the Mawangdui Silk Texts, and they cover not only astrological and astronomical phenomenon but cartography, writing, and mathematics. In total, there are approximately 120,000 words covering these topics, arranged by scholars into 28 types of silk books. The comet drawings, which span several centuries, include such astronomical phenomena as “cloud vapor divinations” and

138

9. Comets

“star divinations,” which would have aided the prediction of victory or defeat in battle. Aeromancy, or “cloud vapor divination,” is the interpretation by an individual as to what form a cloud may take in their eye, indeed, cloud reading. However, more importantly, aeromancy, along with cloud shapes, weather conditions, and atmospheric phenomena, includes such other phenomena as comets and meteors. In medieval times, texts usually spelled “aerimacy” were expanded to include almost all phenomena occurring in the air. “Star divination” is classed as a pseudoscience, claiming divination by the positions of the planets and Sun and Moon. Additional records also exist to accompany the Chinese comet-gazing with details of the catastrophe or disaster thought to be associated with each comet, illustrating the dread and fear once cause by these cosmic “harbingers of doom.” The Chinese also made other such records of the sky. Pottery dating back to the Neolithic period of over 5000 years ago, housed at the Beijing Ancient Observatory, depicts images of the Sun, and intricately carved animal shells and bones display images of the stars as well as astronomical events such as star explosions that may date back as far as 1400 b. c. Based on other cultures and their undertaking of what was eventually to become the science of astronomy, it is quite reasonable to assume that early observations of this type were first undertaken as a way of marking time, with the recording of events used to establish a pattern that, in turn, would create a calendar. The Chinese, like many other civilizations, would have based the calendar primarily around the well-established phases of the Moon. It would be instrumental in aiding farmers with their crop planting and reaping cycles, with a pattern of seasons acting as an overall cohesive structure to the year. The addition of extra months was necessary, as the solar year is not evenly divisible by an exact number of lunar months, so without the extra months, the seasons would drift each year, eventually falling badly out of synchronicity. Therefore, the Chinese calendar had a 13-month year every two or three years in order to maintain the seasons. Making regular observations of the sky also captured other events such as supernova. The Chinese documented them as “guest stars,” with an entire catalog of these explosions maintained over centuries, and just as they used great accuracy to record and plot comets, they offered similar detail with regard to supernova, enabling modern astronomers to find remnants of these outbursts in the sky today.

Chinese Astronomers

139

There was still a lot to be gleaned from this early observational work, but one must acknowledge the substantial contribution of French engineer and sinologist Édouard Constant Biot who made an extensive translation of these ancient Chinese astronomical records. As an engineer, Biot participated in the construction of the second line of French railway between Lyon and St. Etienne, while as a sinologist, he published a large body of work. An extensive series of papers, devoted to astronomy, mathematics, geography, history, social life, and administration of China, led to an elevation of great standing in his chosen subjects. His astronomical translations were useful in associating the Crab Nebula with the supernova observed by the Chinese in 1054. Many subsequent astronomers were to make use of Biot’s translations, including English astronomer John Russell Hind (1823–1895). Hind attempted to correlate observations that had been made by the Chinese every 75  years in an attempt to potentially find a regular visitor to the inner Solar System, that of Halley’s Comet. In doing so, Hind strived to see just how far back he could venture with the Chinese data, and subsequently it is Hind that we have to thank for linking the image of Halley’s Comet to the one on the Bayeux Tapestry. Subsequent astronomers followed Hind’s method, with British astronomer Phillip Herbert Cowell (1870–1949) using such reckoning for the comet’s return in 1910. Later, Tao Kiang (1929–2009) of the Dunsink Observatory in Dublin and Donald Yeomans of the Jet Propulsion Laboratory in America were to also use the records. Hind’s work also incorporated other fields in astronomy. He discovered and observed the variable stars R Leporis (also known as Hind’s Crimson Star), U Geminorum, and T Tauri (also known as Hind’s Variable Nebula). R Leporis resides in the constellation of Lepus near its border with Eridanus. The star is a carbon star that appears distinctly red in color, with numerous references also quoting an intense smoky red color, although only when the star is at its dimmest, not at maximum brightness. Hind himself reported the star as “like a drop of blood on a black field.” The coloration is caused by carbon in the star’s outer atmosphere filtering out the blue part of its visible light spectrum. U Geminorum, in the constellation of Gemini, is a typical example of a dwarf nova, classed as a cataclysmic variable star consisting of a close binary star system in which one of the ­components is a white dwarf that accretes matter from its companion. Hind observed U Geminorum in 1855, but it wasn’t until much later, in 1974, that the mechanism behind the variability

140

9. Comets

was determined, with the white dwarf designated as the primary star and a red dwarf as the companion. T Tauri, in the constellation of Taurus, was discovered by Hind in October 1852, appearing from Earth to be among the Hyades cluster when it is in fact situated at a greater distance behind it, and was formed separately. While it was Hind who discovered T Tauri, the actual classification of variable stars as generally T Tauri type stars (TTS) wasn’t until 1945, when American astronomer Alfred Harrison Joy (1882–1973) first broached the overall definition relating to T Tauri type stars that can be applied to other variables of its kind. One of the attributes is that T Tauri stars are associated with youth, the stars being less than about ten million years old. There is faint nebulosity around T Tauri, known as a Herbig-­ Haro object. Named Burnham’s Nebula or HH (Herbig-Haro) 255, such objects are turbulent looking patches of nebulosity associated with newborn stars. Lasting only briefly in cosmic terms, around a few tens of thousands of years, their shape can change quite noticeably over short timescales. The Hubble Space Telescope has a revealed a complex evolution of HH objects over a period of just a few years, as parts of the nebula fades while other parts brighten. First observed by American astronomer Sherburne Wesley Burnham (1838–1921), Sherburne was to produce a catalog of double stars, called the General Catalogue of 1290 Double Stars, and in 1906, published the Burnham Double Star Catalogue, which contains a staggering 13,665 pairs of double stars, the result of Burnham’s commitment to observing the heavens over a timespan that was to exceed 50  years of his life. From 1872 to 1877, Burnham, using his 5.9-inch telescope, found 451 new binary stars, with a total credit of having discovered ____ binary stars, with a lunar crater and asteroid subsequently named in his honor. Other astronomers of note who also made a significant contribution to the cataloging of binary stars are German-Russian astronomer Friedrich Georg Wilhelm von Struve (1793–1864) and Baltic German astronomer Otto Wilhelm von Struve (1819–1905). The two, father and son, cataloged a good number of binary stars while working in the observatories of Dorpat and Pulkovo. Located in Estonia and renamed the Tartu Observatory (several name changes are recorded for the site over the years), the “Dorpat” observatory is known internationally for its connections with Friedrich Georg Wilhelm von Struve, and notably the Struve Geodetic Arc, of which it remains the first reference point. The Arc is a chain of survey triangulations stretching from

Greek Astronomers

141

Hammerfest in Norway to the Black Sea in the Ukraine, through ten countries and over 2820 km, which yielded the first accurate measurement of a meridian. Von Struve established the chain in the years 1816–1855 in order to calculate the exact size and shape of Earth. In 2005, the chain was added to the World Heritage List, with an inscription that is located on various “structures” in ten countries, the most of any UNESCO World Heritage Site. Opened in 1839, the Pulkova Observatory was the brainchild of Friedrich, who would become its first director, succeeded by his son in 1861. The 15-inch refracting telescope was built in 1839, the largest in the world, and the observatory was notable from the beginning for its quality of observations. Located 19 km from St. Petersburg, the observatory is also part of a UNESCO World Heritage Site. In 1878, a 30-inch refractor was built there, the largest of its kind in the world for about 10 years. During his time, Hind was to discover ten asteroids, although the naming of one of them caused him some controversy. The asteroid in question was discovered on September 13, 1850, with Hind subsequently naming his find 12 Victoria. The asteroid, a large main-belt body, had, according to Hind, been named after the mythological figure of Victoria, not that of Queen Victoria, as asteroids were not supposed to be named after living persons. Despite some anomalies in the research conducted by Hind, essentially, he did revolutionize the whole history of comets. His work was progressed in later years by British astronomer and specialist in the field of mathematics Phillip Herbert Cowell, who also notably discovered asteroid 4358 Lynn, and Andrew Claude de la Cherois Crommelin (1865–1939), also a British astronomer and president of the Royal Astronomical Society from 1929 to 1931. Crommelin, considered at the time to be one of the world’s leading authorities on comets, worked closely with Cowell and made predictions based on the work of the Chinese and other available records, correctly forecasting the return of Halley’s Comet in 1910 to an accuracy of just over 3 days.

Greek Astronomers In ancient Greece, many philosophers turned their attention to finding an explanation for the phenomenon. Aristotle believed they were but emanations from Earth’s atmosphere. Aristotle’s views commanded great respect in the West for more than one-anda-half millennia. However, fellow philosopher Seneca challenged

142

9. Comets

Aristotle’s interpretation of comets, believing them as planetary phenomena that follow regular but unknown orbits. Indeed, Seneca takes the comet out of Aristotle’s context of being atmospheric, progressing the understanding to a literally “higher” plane in celestial theorizing, raising us to a form of celestial insight that is far removed from the “lower” forms of cometary conjecture. According to ancient authors, a meteorite the size of a “wagonload” crashed into northern Greece sometime between 466 and 468 b. c. The impact shocked the local population and the rock, which was described as having a “burnt color,” became a tourist attraction for 500 years. Accounts that describe the meteorite also detail the presence of a comet in the sky, which coincidentally correlates with an appearance of Halley’s Comet. If so, the Greeks could well lay claim to having the earliest documented sighting of the famous visitor. Whereas initial attention towards the archives chiefly center on the meteorite that fell into the northern Hellespont region, curiosity over the visitor gained momentum, as this discovery would strip the Chinese of the title of being the first to spot Halley’s Comet, handing it to the Greeks, a clear two centuries before the Chinese mention it. The earliest credible recording was taken from the Chinese text called Shih chi that discusses sightings of a “broom star” in 240 b. c. The sighting of the broom star is found in the Han dynasty’s “Records of the Grand Historian.” However, according to some scientists, including philosopher Daniel Graham and astronomer Eric Hintz of Brigham Young University, Utah, an ancient Greek text from 466 to 467 b. c. notes that a comet was visible in the Western sky for 75 days around the time of the meteorite impact. It was also noted that the event was accompanied by strong winds and shooting stars. Graham and Hintz used computer modeling to calculate the comet’s historic path, with the results concluding that Halley’s Comet would have been visible from June 4 to August 25, 466 b. c., for a total of 82 days, depending on the weather. In July, the model shows that Earth would have been moving under the comet’s tail, which means meteors shed by the comet may have been peppering the atmosphere, just as meteors from the debris left by Halley’s Comet still interact with Earth’s atmosphere to generate a display of the annual Orionids meteor shower. Speculation surrounds the actual meteorite that crashed, as to whether it was an extremely large fragment of the comet itself

The Middle Ages

143

or another body, such as an asteroid that collided with Halley’s Comet, its course altered into one that would have impacted with Earth. The resulting meteors could well have been heightened in activity with the normal “seeding” debris from Halley’s Comet, plus fragments from the incoming asteroid. However, connecting the two seems to draw little support, with the two appearing at the same time generally accepted as coincidental and nothing more. In ancient Egypt, Pharaonic astronomical texts dating back to the 9th Egyptian dynasty (c. 2150 b. c.) name 36 stars that rise within 10  days of each other at the same time as the Sun. Astronomers under Thutmosis III (1504–1450 b. c.) also recorded the appearance of Halley’s Comet. The discovery of the possible sighting by the Greeks remains in a way quite ironic. Whereas the Chinese and indeed for that matter the Babylonians kept meticulous records of events in the night sky, the Greeks did not. However, with a vast array of documentation recorded, the accolade of which civilization saw Halley’s Comet first is far from being resolved.

The Middle Ages Recordings of comet sightings are abundant in medieval chronicles, where they figure continually as portents of war, pestilence, famines, and the fall of kingdoms. In the Middle Ages, the fear of the “heavy hand of God” reached its pinnacle, with terrible natural phenomena linked with sightings, from great floods to earthquakes. In the Anglo-Saxon Chronicle, comets were noted in the following years: 678, 729, 892, 905, 975, 995, 1066, 1097, 1106, 1110, and 1114. Nine times out of the eleven, the sighting of a comet during these years was treated as a bad omen, marking a death or anticipating a misfortune befalling a prominent figure. Most notable among them is the sighting of Halley’s Comet that appears on the Bayeux Tapestry. The tapestry measures nearly 70  m long and 50  cm tall, depicts the events leading up to the Norman conquest of England. The work features William, Duke of Normandy (1028–1087) and Harold, Earl of Wessex (1022–1066), later kind of England, with the tapestry’s culmination depicting the Battle of Hastings. The tapestry is believed to have been commissioned by Odo of Bayeux (died 1097), Earl of Kent and Bishop of Bayeux, half-brother of William the Conqueror. Thought to date from the eleventh

144

9. Comets

c­ entury, within a few years after the battle, the story unfolds from the point of view of the Normans, but there is now agreement that the tapestry was made in England. Originally, some historians thought that given the fact that the work broadly celebrates and sanctions William’s conquest of England, Queen Matilda (1031– 1083) was behind its origination. Matilda of Flanders was queen of England and duchess of Normandy by marriage to William. In 1729, the work was rediscovered by scholars at a time when it was being displayed annually in Bayeux Cathedral, exhibited in recent times at the Musee de la Tapisserie de Bayeux in Bayeux, Normandy, in France. As to who actually produced the tapestry, there remains great uncertaintly. Although not really a tapestry, more an embroidery, the work is comprised of 1515 objects, animals, and figures, including the significant astronomical event, that of the return and sighting of Halley’s Comet. Depicted as a quite strange but unmistakable object on the tapestry, with historical accounts mentioning that the comet appeared to be four times the size of Venus, Halley’s Comet has a group of messengers pointing at it. Interestingly, the appearance of the scene depicting the comet is out of chronological sequence with the other events in the tapestry. The comet is shown just after the scene that depicts Harold’s coronation, when in actuality it appeared about four and a half months later. The inclusion of the comet at this point in the tapestry, though, was meant to display divine judgement and foreshadow the impending evil that would follow Harold’s perjury.

Early Modern Period Petrus Apianus (1495–1552), also known as Peter Apian, Peter Bennewitz, and Peter Bienewitz, was the first astronomer to observe that comets’ tails always pointed away from the Sun, something he noticed when documenting the 1531 return of Halley’s Comet. He wrote about this in his book Astronomicum Caesareum, which was published in 1540 and dedicated to Emperor Charles V. His work was extremely influential, with numerous editions in multiple languages being published until 1609. The work is noted for its visual appeal and is widely considered by many as perhaps the most beautiful scientific book ever printed. Taking 8 years to create, Astronomicum Caesareum isn’t just considered a scientific manual; it is also considered a great work of art, featuring

Early Modern Period

145

ingenious and beautiful volvelles, or wheel charts (a type of slide chart of paper construction with rotating parts) that allowed users to calculate dates, the positions of the constellations, and other such usages. Printed and bound decoratively, Apianus noted that it took a month to produce some of the plates for Astronomicum Caesareum. Thirty-five octagonal paper cut instruments were included with woodcuts that are thought to have been made by German draughtsman, printmaker, and painter Hans Brosamer (1495–1554). During his lifetime, Brosamer’s work included over 600 woodcuts, mainly in the form of illustrations for books. However, it is also worth noting that another name has been associated with the hand-colored woodcuts, that of Michael Ostendorfer (1490–1549). When describing records made of the night sky that span the centuries, whether they be graphic representations on cave walls or highly sophisticated data relayed through the depths of space by a probe far from Earth, Astronomicum Caesareum is, in publishing terms, a rare and exquisite gem. The volvelles contain as many as five independently rotatable dials that can be used to measure astronomical movements. The silk strings provide fiducial lines (a line assumed as a fixed base for comparison), and the strings are threaded with pearls to mark a point on the line. The volvelles and supporting tables can be used also to calculate eclipses, and Apianus devotes two chapters to the correction of historical dates by referencing these phenomena. Three decades later, Danish astronomer Tycho Brahe measured the parallax of a comet that appeared in 1577 a. d. to be around 230 Earth radii, corresponding to 1.5  million km. The comet, which was subsequently called the Great Comet of 1577, was a non-­periodic comet that was viewed by citizens across Europe, famously so that of Tycho Brahe, and also Ottoman Polymath Taqi al-Din Muhammad ibn Ma’ruf ash-Shami (1526–1585). Al-Din was the author of over 90 books on a variety of subjects including astronomy, using his exceptional knowledge in the mechanical arts to construct instruments used to observe the comet. Using all available records to estimate the orbit of the comet, it seems that the perihelion for the visitor was on October 27 1577, with the first recorded sighting made 5 days later from Peru. Observers at the time noted that the comet could be seen through the clouds, like the Moon. On November 7, 1577, from Ferrara, Italy, architect and painter Pirro Ligorio (1512/13–1583) described “the comet shimmering from a burning fire inside the dazzling

146

9. Comets

cloud.” On November 8, 1577, the Japanese reported a Moon-like brightness and a white tail spanning over 60 degrees. Brahe was said to have first sighted the Great Comet of 1577 slightly before sunset on November 13, after having returned from a day’s fishing. Brahe’s contributions to recording the apparition include sketches in notebooks that seem to indicate that the comet may have traveled close to Venus. The sketches depict Earth at the center of the Solar System, with the Sun and the Moon in orbit, and the other planets revolving around the Sun. Among Brahe’s archives are literally thousands of very precise measurements of the comet’s path. His discovery that the comet’s coma faced away from the Sun was also to be a significant find. Brahe’s measurement of the Great Comet of 1577 refuted the teachings of Aristotle and proved that comets weren’t generated “within” the terrestrial atmosphere, but were themselves independent celestial bodies. Additionally, comets even turned out to be translunar objects, meaning they stayed beyond the Moon. Brahe established this by comparing the position of the comet in the night sky in two different observational sites. Brahe, while observing from the island Hven, near Copenhagen, made his comparison with that of Czech naturalist and astronomer Thadaeous Hagecius (1525–1600), who was observing the comet at the same time in Prague. Giving deliberate consideration to the position and movement of the Moon, it was discovered that while the comet was in approximately the same place for both Brahe and Hagecius, the Moon was not, and this meant that the comet was much further out! Brahe also put forward a theory to explain the possible trajectory that comets followed through space, being the first to believe that comets returned periodically. Brahe’s thoughts were at odds with those of Johannes Kepler, who believed that the trajectories were straight lines, thus inadvertently contradicting his own laws, which assigned elliptical orbits to the planets! The argument was later settled by astronomer and mayor of Danzig Johannes Hevelius, who proposed that comets traveled in elongated parabolas and hyperbolas, as we now know they do. Published in 1665, the whole argument had been fueled by Hevelius’ Cometographia, a work that on its title page referred to the trajectory of comets and the cause of their trails. Hevelius during his time also gained a reputation as the founder of lunar topography, also describing in his time ten new constellations, seven of which are still used by astronomers today.

Early Modern Period

147

Other notable sightings of the Great Comet of 1577 include that of Sultan Murad III (1546–1595), who said the observations were a bad omen for war and blamed al-Din for a plague at the time. Murad III was sultan of the Ottoman Empire from 1574 until his death in 1595. The war in question was the Ottoman-Safavid War (1578–90), one of many wars between neighboring archrivals of Safavid, Persia, and the Ottoman Empire. The war itself ended in an Ottoman victory and the Treaty of Istanbul (1590). German physician and astrologer Helisaeus Roeslin, who had adopted a geoheliocentric model of the universe, was one of five observers who concluded that the Great Comet was located beyond the Moon. His own representation of the comet, described as “an interesting, though crude, attempt” was among the earliest and was highly complex. Roeslin had known Kepler since their student days, and like several of his contemporaries, was a correspondent of his. However, Roeslin had more of a leaning towards astrological predictions than Kepler, who himself was a respected mathematician. Roeslin rejected some of Kepler’s principles, including the Copernican theory. In his book De Stella Nova in Pede Serpentarii (“On the New Star in the Foot of the Serpent Handler”), Kepler openly criticized Roeslin’s predictions surrounding a later comet, which appeared in 1604. Arguments between the two were kept alive in a series of pamphlets written as dialogs. Written between 1605 and 1606 and published in Prague, De Stella Nova, as it’s more commonly referred to, mainly focused as the title suggests on the appearance of supernova SN 1604, also known as Kepler’s Supernova. In terms of records throughout the centuries, De Stella Nova is incredibly important, as both a record of the supernova itself, and of astronomy in the early seventeenth century. One of Roeslin’s own publications, De opere Dei creationis (1597), is regarded as one of the major works of the sixteenth century controversy over the formulation of a geoheliocentric world system. Roeslin was to make a prediction following the appearance in early November 1572 of one of only eight supernovae recorded as being visible to the naked eye in historical records. He said that following the event, the world would end in 1654. Referred to as the appearance of a “new star” the supernova of 1572, in the constellation of Cassiopeia, ranks among the most important observation events in the history of astronomy.

148

9. Comets

It helped revise ancient models of the heavens and helped to speed on a revolution in astronomy that began with the realization of the need to produce better astrometric star catalogs, and following on from better catalogs, more precise astronomical instruments. The supernova also challenged the Aristotelian dogma of the unchangeability of the realm of the stars. Often referred to as “Tycho’s supernova,” because of Tycho Brahe’s extensive work De nova et nullius aevi memoria prius visa stella (“Concerning the Star, new and never seen in the life or memory of anyone”), published in 1573, the remnant of the supernova had been observed optically but was first detected at radio wavelengths. How ironic that this work, published in 1573, could have such a parallel with another completely different method of recording the skies centuries later. Although not the first to observe the 1572 supernova, it is considered that Brahe’s observations were probably the most detailed and accurate. After Roeslin’s death, German author, physician, and collector of manuscripts Karl Widemann (1555–1637) published Roeslin’s unpublished works, covering such topics as astrology, theology, and Kabbalism. William IV of Hesse-Kassel (1532–1592) also saw the Great Comet of 1577, and his interest in astronomy and the sciences in general is thought to have perhaps been an inspiration for Astronomicum Caesareum. William was a pioneer in astronomical research with his own contribution being the Hessian star catalog, listing about a thousand stars. His work was published in Historia coelestis in 1666 by German astronomer Albert Curtz (1600–1671). Curtz is also credited with his expansion on the works of Brahe and using the pseudonym Lucius Barretus. The Latin version of the name Albert Curtz, Albertus Curtius is an anagram of his pseudonym, Lucius Barretus! Curtius, a lunar impact crater located on the southern part of the Moon, is named after him. Physician, astronomer, and astrologer Cornelius Gemma (1535–1578) witnessed the comet, noting that the visitor had two tails. Along with German astronomer and mathematician Michael Maestlin (1550–1631), he, too, identified the comet as superlunary. Gemma made significant contributions with his observations of the lunar eclipse in 1569 and of the 1572 supernova, which he recorded on November 9, 2 days before Brahe, calling it a “New Venus.” Gemma is also credited with publishing the first scientific illustration of the aurora in his 1575 book on the supernova. Maestlin also made significant contributions to astronomy, cataloguing the

Late Modern Period

149

Pleaides cluster on December 24, 1579. Eleven stars in the cluster were recorded by Maestlin, and possibly as many as 14 were observed. Maestlin, a student of Apianus, author of Astronomicum Caesareum, also observed the occultation of Mars by Venus on October 13, 1590, seen by Maestlin from Heidelberg. He, too, has an impact crater named after him, situated near the eastern edge of the lunar Oceanus Procellarum. The comet’s passage was also observed by Abu’l-Fazi ibn Mubarak (1551–1602), who in Akbarnama (which translates to Book of Akbar, the official chronicle of the reign of Akbar, the third Mughal emperor (reigned 1556–1605)) recorded the sighting.

Late Modern Period The work of Johann Franz Encke (1791–1865) was in later years to endorse the findings of Halley with regard to periodic comets. Encke made a study of a comet that had been discovered by French astronomer Jean-Louis Pons (1761–1831) in 1818. Pons, who was self-taught, is considered to be one of the greatest visual comet discoverers of all time, notching an impressive 37 comet finds between 1801 and 1827, more than anyone in history. His first discovery was made on July 11, 1801, a find jointly attributed to Charles Messier. Pons used telescopes and lenses of his design. His so-called “Grand Chercheur” (“Great Seeker”) seems to have been an instrument with a large aperture and short focal length, similar to the “comet seeker,” another type of telescope adapted especially for searching for comets, its short focal length and large aperture securing the observer the greatest amount of light when observing the skies. Encke determined that the 1818 comet, discovered by Pons on November 26, did not seem to follow a parabolic orbit, suggesting that it was indeed following the path of a closed ellipse. Furthermore, with an orbit of 3.3 years, it had most probably been observed many times before, but without any link being established to the fact that it was probably the same comet. Encke recounted observations made by French astronomer Pierre Mechain (1744–1804) in 1786 and German astronomer Caroline Herschel in 1795. Despite his calculations being rewarded with the comet being named after him, Encke continued to refer to the comet as “Pons’ Comet,” relating to another much earlier sighting of the comet made by Pons in 1805.

150

9. Comets

Encke remained puzzled as to why, during subsequent visits, the orbit of the comet appeared to be shrinking, with each return shaving several hours off previous orbital calculations. Encke was to notice such a small shortening of the orbit firstly because of the frequency of visits made by the comet, and secondly – and more importantly – because of Newton’s law of gravity, which takes into account other potential influences from planetary bodies. Another question concerned the reason behind the comet’s apparently slow winding down in a spiral towards the Sun, a trait also displayed by Halley’s Comet. Was this an outside force working on the comet, or simply a loss of mass affecting orbital patterns? German astronomer, mathematician, physicist, and geodesist Friedrich Wilhelm Bessel (1784–1846) suggested that the expulsion of material from a comet near to perihelion was acting like the motor of a rocket, each time upon rounding the Sun, propelling it into a different orbit. Bessel’s proposal was right. Bessel’s own interest in comets, among his other achievements, is notable. In 1804, he wrote a paper on Halley’s Comet, calculating the orbit using data from observations made by English astronomer and mathematician Thomas Harriot (1560–1621). Harriot himself was notably the first person to make a drawing of the Moon through a telescope, on July 26, 1609, over 4 months before Galileo Galilei. A comet first recorded by French amateur astronomers Jacques Lebaix Montaigne (1716–1785) and Charles Messier in 1772, then later sighted by Jean-Louis Pons in 1805, it was eventually shown by Austrian military officer and astronomer Baron Wilhelm von Biela (1782–1856) in 1826 that all of the sightings were of a periodic comet, falling into the same category as Encke’s and Halley’s Comet, respectively. Biela, having identified that the comet had an orbital period of around 6.6 years, predicted that it would return in 1832, and it duly did so. After a poor apparition in 1839, the comet was recovered in the skies on November 26, 1845, by Italian astronomer Francesco de Vico (1805–1848). Vico is remembered for finding a remarkable number of comets in a relatively short space of time, including, initially, the sighting of a new comet later to be named “Miss Mitchell’s Comet.” Vico, observing from Rome, was the first to report the comet’s discovery in Europe in 1847. However, it had been sighted by American astronomer Maria Mitchell (1818–1889) two days earlier, earning the comet its name. Mitchell, the first

Late Modern Period

151

American woman to work as professional astronomer, was duly presented with a gold medal for her discovery by King Frederick VI (1768–1839) of Denmark, on which was inscribed in Latin “Non Frustra Signorum Obitus Speculamur et Ortus” (“Not in vain do we watch the setting and rising [of the stars]”) At the time of the sighting of Biela’s Comet in 1845, and due to its faintness in the skies, nothing seemed out of place. However, observations made by American astronomer and naval officer Matthew Fontaine Maury (1806–1873) on January 14, 1846, noted that there was something unusual, the fact that the comet was not alone, noting that a companion body was present. With the astronomical world intrigued, many astronomers turned their attention to the apparent fragmentation of the comet. It seemed the comet had broken up into two separate components during its journey, both fragments still traveling together along Biela’s predicted orbital path. The two portions of the comet (now named “Comet A” and “Comet B”) traveled successfully around the Sun and left as they had arrived. Biela’s Comet was rediscovered on its return in 1852 by Italian astronomer Angelo Secchi (1818–1878) – first “Comet A” on August 26, then “Comet B” on September 16. Although other segments could well have existed but were too faint to spot, A and B alternated in brightness during the period of observation, with A last seen on September 26 and B on September 29. In both cases, it was Otto Wilhelm von Struve who made these final sightings as, following the visit of 1852, the double comet was never seen again. The expected return in 1859 and 1865 produced no comet. The comet’s break-up and subsequent disintegration left a serious question mark over what had happened to the body during its orbit. Subsequent orbital calculations indicated that the nuclei had probably split around 500 days before the 1845 apparition, with later models suggesting the comet had split earlier, near aphelion in late 1842. However, during a scheduled return of Biela’s Comet in 1872, and as if to mark its demise, a glorious shower of meteors, boasting an hourly rate of 3000, lit up the skies in November 1872, more or less where the comet was supposed to have reappeared, and just 2 months after Biela was due to cross the skies in October. The Bielid shower is more commonly known as the Andromedids, as they radiate from the constellation of Andromeda, although the stream itself has significantly faded.

152

9. Comets

At the time of heightened awareness around Biela’s Comet, the potential destructive capabilities of the comet became a hot topic of discussion, with a possible impact risk from stray fragments of the comet. On November 27, 1885, an iron meteorite fell in northern Mexico, at the same time as an outburst from the Andromedid meteor shower, when a documented 15,000 meteors per hour were sighted. The Mazapil meteorite (named after Mazapil, a municipality in the Mexican state of Zacaecas) was initially linked with Comet Biela, but the theory has fallen out of favor over the years, as the processes of differentiation required to produce an iron body are not believed to occur in comets.

Comet of 1910 Imagine a world where a revolution in communications technology is taking place, where the globe is being transformed. Countries that seem far apart and remote are on the verge of being connected and drawn closer together, where sound and vision pierce the darkness, forging ties for better or worse across continents, and drawing nations to take more than just a passing interest in those in far distant corners. The comet of 1910, also known as the Daylight Comet, appeared when there was much expectation around the return of Halley’s Comet. There was considerable media interest in the return of Halley, which was in turn passed onto the public, and so much so was the preoccupation with Halley’s that the Daylight Comet came as something of a surprise. The Daylight Comet has many claimants to its discovery, but it is thought to have first been witnessed by diamond miners in the Transvaal before dawn on January 12, 1910, by which time it was already a naked-eye object. It was Scottish astronomer Robert Thorton Ayton Innes (1816–1933) who is credited as the first astronomer to sight the comet, observing from the Transvaal Observatory in Johannesburg on January 17. In 2007, Comet McNaught became the brightest comet in over 40  years, easily visible to the naked eye in broad daylight. Named after the prolific discover of comets, Scottish-Australian astronomer Richard McNaught (born 1956), the Great Comet of 2010 was the second brightest comet since 1935, discovered while McNaught was making a routine sweep of the sky from Siding Spring Observatory (Fig. 9.1).

Comet of 1910

153

Fig. 9.1.  Comet McNaught. (Courtesy of Steph Seip/David Levy)

Innes had turned his attention to the comet after being alerted two days previously by the editor of a Johannesburg newspaper. On the morning of January 17, and perhaps believing that the sighting was a mistake, as Halley’s Comet was not due for several months yet, an assistant to Innes spotted the comet, shining above the horizon just above where the Sun would shortly rise. Later at midday, Innes viewed the comet as a snowy-white object, brighter than Venus, several degrees from the Sun. He sent out a telegram alerting the world to its presence, stating that a “Great Comet” had been sighted, although “Great Comet” was interpreted as “Drake’s Comet” by the telegraph operator, so a correction was necessary. The Daylight Comet had brightened rather suddenly when it was first visible in the southern hemisphere, and after reaching perihelion on January 17, was to adorn the northern hemisphere skies with a majestic sweeping tail that reached up to 50 degrees in length by early February. At its brightest, the comet outshone Venus and was viewed by millions across the globe.

154

9. Comets

With the media already on a heightened state of readiness ahead of Halley’s return, when Halley’s comet did arrive, the stage seemed set for another dose of ‘comet fever.’ However, some of the press were to see Halley’s arrival rather differently, latching on to the some of the doom merchants with talk of the comet’s tail encountering Earth, a tail which contained poisonous gases! With telescopes very much in demand and a public eager to purchase them, hotels in large cities offered special packages that included rooftop viewings of the comet. Elsewhere, anti-comet pills were being hawked! However, not all adopted such a stance, as there was a mix of songs to serenade the heavenly visitor, and poetry also versed for the comet’s arrival. The appearance of both comets certainly caused a stir in 1910, but unlike perhaps other phenomena in the night sky, it’s a fascination with this particular heavenly body that was to engage the world in wonderment.

The Ultimate Recording Methodology? Of the records that exist on comets throughout history, no other comet has utilized such a variety of recording methods for one body as Halley’s has. Halley’s Comet has been sighted by many civilizations over thousands of years, and by charting how our ancient ancestors saw, perceived, and ultimately documented Halley, this surely delivers the zenith in astronomical archives beyond the recording of our own Moon, Sun, and Solar System throughout the generations. For here, we have a returning body that on each approach is greeted differently, and viewed each time with new eyes, new thoughts, and new concepts. From stone tablets, to a woven tapestry, from scribed parchment to humankind dispatching probes to visit Halley’s, no greater benchmark exists for such a phenomenon, which through its own reoccurring presence has offered itself time and time again as a spectacle to be painted, drawn, sketched, written, televised, filmed, and eventually “made contact with.” Cometary references by ancient astronomers are few, with so much of the potentially detailed work that would confirm such sightings of Halley’s Comet at that period lost to the ravages of time, or simply undiscovered. A brief Chinese account dating from 240 b. c. remains the earliest identifiable record of Halley’s Comet, before the Babylonian tablets of 164 b. c. and 87 b. c.

The Ultimate Recording Methodology?

155

The 240 b. c. recording of the return of the comet mentions an appearance in the eastern aspect of the sky between May 24 and June 23. After conjunction, a further 16 days of observations on the comet were collected during its western apparition. Perihelion for the 240 b. c. return occurred on May 25, with the comet’s closest approach to Earth measured at a distance of under 67 million km. The next return saw Halley’s Comet come even closer, at under 16 million km. The 198 b. c. return saw Halley’s Comet first sighted in the constellation of Taurus to the east, in the area of the Pleiades, and later sighted to the west in Sagittarius between October 21 and November 19. There is no reference on either Babylonian tablet as to the dates of the comet’s first sighting to the east, but the second sighting dates are mentioned, with a general idea of when it was probably seen. The 87 b. c. return of Halley’s Comet was at a distance more in line with that of the 240 b. c. return, with a closest approach measured at less than 67  million km. Chinese accounts at the time recollect the sight of a comet in the eastern aspect of the sky. The Han-shu records reference the comet thus: “In autumn during the seventh month (August 10 to September 8) there was a ‘bushy star’ in the east.” The Babylonian account, despite coming from only a fragment of a tablet, talks of the comet’s tail, with its position noted sometime between July 14 and August 11, perihelion occurring on August 6. The 12 b. c. apparition of the comet was chiefly documented by the Chinese, Babylonian records seemingly having not survived the passage of time, although it is fair to say that it is likely that an account was made. The motion of the comet during this return is accurately accounted for by the Chinese, as it moved from Gemini to Scorpius. The comet’s first appearance was documented on August 26; its last charted appearance before fading out of sight was noted on October 20. These exact dates give a total duration of visibility for Halley’s Comet during this visit at 56 days. The comet’s closest approach to Earth occurred at 24 million km, with perihelion on October 10. The return was considered among a number of portents preceding the death of Roman statesman Marcus Vipsanius Agrippa (63–12 b. c.). An account at the time reads: “The star called comet hung for several days over the city and was finally dissolved in flashes resembling torches.”

156

9. Comets

Halley’s Comet next returned in b. c., first sighted on January 31, with the last documented sighting on April 10, having passed through several zodiacal signs. Perihelion occurred on km. During this apparition, Roman-Jewish scholar and historian Titus Flavius Josephus (a. d. 37–100), who lived through the siege and fall of Jerusalem, makes reference to the comet’s apparition. He mentions several portents leading up to these events, one of his descriptions noting a phenomenon in the sky, possibly referring to Halley’s Comet. While only speculation exists about what he was actually referring to, it seems a distinct likelihood that it was Halley’s. His reference to a “star resembling a sword” is quite striking in more ways than one. During the a. d. 141 return, references were made by Chinese records on the color of the comet, detailing it as “pale blue.” The Chinese also made a very accurate measurement of the comet’s nucleus. First sighted on March 27 to the east, last visible on April 22 to the west, perihelion occurred on March 22, with the comet’s closest distance to Earth measured at under 25 million km. For the a. d. 218 return of Halley’s Comet, we rely mainly on the Chinese for records of any substance, with the first sighting noted on April 14. Visible in the western aspect of the sky, the comet’s motion is logged as being sighted between the constellations of Auriga and Virgo. Perihelion occurred on May 17, with the closest distance from Earth measured at within 64 million km. There is reference to the comet being sighted from Europe during this return in the contemporary work of Lucius Cassius Dio, a Roman statesman and historian. Dio, who was to publish 80 volumes of his Roman History during his lifetime, lists the comet as a portent signaling the death of emperor Caesar Marcus Opellius Severus Macrinus Augustus (Emperor Macrinus, 165–218 a. d.). A fairly unremarkable return was noted by the Chinese for a. d. 295, strangely sketchy in any detail, with only the month of discovery (May) documenting the comet’s appearance. First seen in the constellation of Andromeda, last seen in Leo, it is not known whether the lack of information on the return is because of a particularly poor apparition of the comet, or whether records of any substance simply haven’t survived. Equally, and not impossibly, sustained poor weather conditions may have been to blame. A very close approach of Halley’s Comet occurred in a. d. 374, with the comet literally skimming Earth at just over 12 million km at its nearest encounter. At this distance, the comet must have presented itself with one of its most splendid appearances

The Ultimate Recording Methodology?

157

in our skies, with Chinese records referencing a “bushy star” sighted in Aquarius on March 6, then a “broom star” sighted in Libra on April 2. Another comet is also documented at this time, which probably goes some way to confusing records of the period. However, this other comet seemed to have had different motions, and, as there are references to this second comet appearing in different parts of the sky, we can rule it out as being associated with Halley’s in any way, The 451 a. d. return of Halley’s Comet is well documented. This apparition also coincided with the time of the Battle of Chalons, in which Roman general Flavius Aetius (a. d. 391–454) engaged his 50,000-plus troops against Attila the Hun (a. d. 406– 453) and a similarly numbered compliment of men. Attila was defeated at the battle. References are made to a comet being seen around June 10. This return also saw, according to documents, the comet in the skies for more than 2 months. However, it was not a particularly near encounter with Earth, similar to the comet’s previous return, some 74 million km at closest approach during this apparition, with perihelion on June 28. From its “pale blue” appearance of a. d. 141 to a “pure white” offering during the return of a. d. 530, the Byzantine chroniclers of the time describe what they saw in September of that year as a “huge and terrible star” whose rays (tail) extended towards the zenith. Visible for a total of 20 days, the chroniclers referred to the comet as Lampadias, as it resembled a burning torch in the sky. Halley’s Comet next appeared in a. d. 607, and despite its distance from Earth measuring just over 12 million km, in line with the approach of a. d. 374, accounts of the return from the Chinese and from observers in Europe lapse into another vague phase of documentation, with the comet on view for what appears to be 2 months. There are also references to other comets being sighted at this time. Although the a. d. 684 return seems to have been virtually unreported across Europe, it was documented for the first time by the Japanese, with a reference made also to a different comet sighted at this time. There is a reference made to this other comet in the Life of Pope Benedict II (a. d. 635–685). The account refers to the comet as being “an absolutely shadowy star, resembling the Moon when covered with clouds.” Halley’s Comet was first depicted in the Nuremburg Chronicle on this return, although there is speculation with regard to a link between this sighting

158

9. Comets

and the date of the chronicle. There is a possibility that there are other, earlier, recorded sightings in the chronicle, but the a. d. 684 drawings do seem to tie in with this apparition. First sighted by the Chinese, and indeed the Japanese, in September 684, the comet made for a spectacle the western sky, with an impressive tail of some 10 degrees. Referred to as a “glittering beam” by Byzantine chroniclers, the a. d. 760 return saw the comet on view for 50  days  – first sighted in Aries, then much later in Virgo. With the sighting of another comet also noted during this time, this particular appearance of Halley’s Comet is regarded as having serious astrological consequences, especially since later in the year, on August 15, a solar eclipse occurred. The sight of two comets at once caused a great deal of disquiet, perhaps because of the impressive spectacle that it created, with both Halley’s Comet and the other comet viewed in separate parts of the sky. From under 61 million km at closest approach to the Earth in a. d. 760, the return of a. d. 837 was to see Halley’s make its closest known approach in history, barely 10 times the Moon’s distance, at just over five million km. With Earth’s gravitational field having a distinct influence on the comet, this is perhaps responsible for the comet’s trajectory being altered, so much so that it might never make such a close approach to Earth again. Although other outside influences may still reshape future returns of Halley’s Comet, the encounter of a. d. 837 must still have been a magnificent sight, with the comet speeding across the sky at around 2 degrees an hour, sporting a tail spanning some 60 degrees, with a distinct second tail also visible. Sightings were recorded in China, Japan, Germany, the Byzantine Empire, and the Middle East. Holy Roman Emperor Louis the Pious (778–840) feared the comet was a signal of his downfall and tried to ward off its influence with fasting, prayer, and alms for the poor. With observations made throughout Europe and the East, the encounter of a. d. 837 is also a significant reminder that, even if periodic comets follow a reasonably stable orbit, gravitational forces from other bodies can have grave influences in altering orbital paths. If Halley’s Comet on this return had arrived a week earlier or less, it would have passed in between Earth and the Moon, with, at this distance, gravity causing a considerably more radical shift to the comet, although only conjecture can surmise whether that effect would have been positive or negative in influence on future Earth encounters.

The Ultimate Recording Methodology?

159

The return of Halley’s Comet is not well referenced in a.d. 912, with the only a small amount of documented evidence. However, there are references to the comet made by the Japanese, and a further reference by Baghdad chronicler Ibn al-Jawzi (a. d.1116–1201), an Islamic scholar and prolific writer, author of over 700 books, to not one but three comets. The return was also captured in the Annals of Ulster, which state “A dark and rainy year. A comet appeared.” The annals reflect the times of medieval Ireland, written in Irish, with some entries in Latin. Despite the Chinese rediscovering the comet in a. d. 989, it is an Arab chronicle record that notes a “planet with a tail,” sighted and tracked over Cairo for 22 days. After the very much documented return of Halley’s Comet in 1066, the comet’s next apparition in 1145 was recorded by the scribe Eadwine, a monk of Christ Church, Canterbury, in England (now Canterbury Cathedral). A reference is made by Eadwine in the form of a drawing of the comet accompanied by a note in Old English (in which it is a “hairy star”), which is an augury. Augury is the practice from the ancient Roman practice of interpreting omens from the observed flight of birds. Following the visitation by Halley’s Comet in 1066, the English evidently took comets seriously. This was thought to relate to the appearance of Halley’s Comet in 1145, but another of May 14, 1147, is recorded in the Christ Church Annals, and the 1145 one is not. There are further comets recorded in 1165 and 1167, so the evidence from astronomy has not settled the question. All of these findings are included in the Eadwine Psalter, a heavily illuminated twelfth century psalter (volume containing book of Psalms), named after Eadwine, who was thought to be perhaps the “project manager” on the work. The dating of the manuscript has been much discussed, mainly on stylistic grounds (regarding both the script and the illustrations). Ultimately, the Eadwine Psalter was left unfinished in England, like many other ambitious manuscript projects. The comet’s 1222 appearance is sometimes credited with inspiring Genghis Khan to send his Mongols to invade Europe, and its 1456 return famously overlapped with the Ottoman Empire’s invasion of the Balkans. Italian artist Giotto di Bondone (1267– 1337) painted the Adoration of the Magi between 1305 and 1306, depicting the comet as the Star of Bethlehem in the nativity scene. The image is believed to have been inspired by the artist’s observation of the passage of Halley’s Comet in 1301. In 1378, the comet is recorded in the Annales Mediolanenses as well as in East Asian sources.

160

9. Comets

Western records of Halley’s Comet were virtually non-­ existent or at least far less detailed than those that the Chinese had been making, that is, until the return of the comet in 1456. Italian physician, astronomer, mapmaker, and mathematician Paolo dal Pozzo Toscanelli (1397–1482) was to sight the comet and, over a period of a month, make a detailed study of its movement across the heavens. Toscanelli calculated its positional measurements to within a degree, marking the first time such detailed data was collected, a significant shift in accuracy, away from the traditional style of observation used by Oriental astronomers. The 1456 return of the comet also saw the Ottoman Empire invading the kingdom of Hungary, culminating in the Siege of Belgrade in July of that year. According to one story that first appeared in a 1475 posthumous biography and was subsequently embellished and popularized by French scholar Pierre-Simon, Marquis de Laplace (1749–1827). Pope Callixtus III (1378–1458) excommunicated the 1456 appearance of Halley’s Comet, believing it to be an ill omen for the Christian defenders of Belgrade. However, no known primary source supports the authenticity of this account. In a papal bull, a type of public decree or charter issued by a pope named after the leaden seal (bulla), Callixtus III, on June 29, 1456, called for a public prayer for the success of the crusade, but contained within it is no reference to the comet. By August 6, when the Turkish siege was broken, the comet had not been visible in either Europe or Turkey for several weeks. Halley’s Comet was also sighted in Kashmir and was depicted in great detail by Srivara, a Sanskrit poet and biographer to the sultans of Kashmir. He read the apparition as a cometary portent of doom foreshadowing the imminent fall of Sultan Zayn al-Abidin (1418/1420–1470). After witnessing a bright light in the sky, which most historians agree as being Halley’s Comet, Zara Yaqob (1399–1468), emperor of Ethiopia from 1434 to 1468, founded the city of Debre Berhan (“City of Light”) and made it his capital for the remainder of his reign. There is a credible reference made to Halley’s Comet during its apparition of 1531. Guru Nanak (1469–1539) refers to lamma tara (“long star”) in one of the hymns in the Sri Guru Granth Sahib. Guru Nanak was the founder of Sikhism and the first of the ten Sikh gurus. His words are registered in the form of 974 poetic hymns in the holy text of Sikhism, known as the Sri Guru Granth Sahib.

The Ultimate Recording Methodology?

161

The 1531 return, as previously mentioned, also had a great bearing on certain aspects of cometary observations, with German astronomer Peter Apian’s notable documention that cometary tails always point away from the Sun, a reference later published in detail in his great work Astronomicum Caesareum. The drawing in Astronomicum Caesareum of Halley’s Comet with its angled tails pointing away from the Sun is as lavish as the rest of the illustrations contained within the publication. Thomas Harriot left the science world an account of the return of Halley’s Comet in 1607, along with the Great Comet of 1618. The 1607 papers contain a record of the observations, a log of seeing conditions, and some preliminary calculations, while the 1618 papers are much more extensive. From September 6–25, the Great Comet of 1618 was visible to the naked eye. In 1618, at least three comets were known to have caused alarm among citizens, 1618 marking the start of the 30 Years’ War. English scientist Sir Isaac Newton (1642- a. d.1727) stated that four comets were visible during the year, “the second and fourth were probably the same” having probably rounded the Sun and simply reappeared on the other side. In 1680, Halley’s Comet appeared brightly in the sky. Sir Isaac Newton noticed the comet on November 19, and over the next week it disappeared behind the Sun. A comet was observed coming out the other side of the Sun in December 1680. If this was the same comet then its path must have been surely bent a great deal in order for it to go around the Sun and reappear on the other side. Also in 1680, 24-year-old Sir Edmond Halley (1656–1742) observed a large comet. With both Brahe and Kepler unable to offer any solid explanation for the behavior of comets, it wasn’t until Newton used his new law of gravity that a solution to the problem was to be presented that all could agree upon. Newton, along with friend and colleague Halley, set about explaining the orbits of comets, also accounting for their one-off appearance or subsequent reappearance. Newton tried desperately to have the 1680 comet run on a straight trajectory, as Kepler had demanded six decades before. But it wasn’t to be, with Halley pointing out to Newton during one of their meetings that the 1680 comet probably had a “sharply curved” trajectory, not straight at all! Newton realized that a force, which he called gravity, must have been responsible. Newton’s discovery of gravity was nothing to do with an apple falling – it was made by making careful observations of comets.

162

9. Comets

Using the new law of gravity, Halley set about working out the orbits of 24 comets that had been observed from 1337 to 1698, applying the principle to each one. However, with poorly detailed observational records that left a great deal of room for speculation and conjecture, Halley was unable to place any of the comets into separate categories, let alone define any projected orbits. In 1705, Halley published his observations in a book entitled Synopsis of the Astronomy of Comets. However, during the study of the 24 comets, Halley had interestingly enough noted that the comets of 1531, 1607, and 1682 did have orbits that made them appear at approximately 76-year intervals, leading Halley to conclude that the comet was one and the same, appearing at regular intervals; indeed, perhaps here was the proof of not only a curved orbit but also of a periodic comet. With these new calculations, Halley made the prediction that this comet did travel in an elongated orbit and therefore predicted that in 1758 it would return to our skies. During the interim time before the comet was to return, Halley was appointed second Astronomer Royal, serving as such between 1720 and 1742, a prestigious position first held by John Flamsteed from 1675–1719. Right on cue, the comet returned with perihelion occurring on March 13, 1759. However, it was the evening of December 25, 1758, that is of particular significance, as it was German amateur astronomer Johann Georg Palitzsch (1723–1788) who discovered a weak spot of light in the constellation of Pisces at the very moment the then unnamed Halley’s Comet was returning. Raised by a strict father to be a Saxon farmer, Palitzsch had secretly studied as much astronomy as he could from the books he could afford. It would appear all the covert work paid off, ultimately propelling Palitzsch onto the astronomical stage with the recovery of the comet. Having learned contemporary astronomy from the book Vorhof Der Sternwissenschaft (“The Forecourt of Astronomy”) by Christian Pescheck, his own determination is testimony to exactly what can be achieved through amateur astronomy, and yet another example of the valuable contributions made from the world outside of the professional. A lunar impact crater in the southeastern part of the Moon has been named after him, along with asteroid 11,970 Palitzsch. Deserved testimony to the man who rediscovered Halley’s Comet. Sadly, Halley was not to see the fruit of his labors, passing away at the age of 85 in 1742. He did not live long enough to see his triumph in celestial mechanics, but his work was to set a milestone in revolutionizing the field of cometary studies.

10. Astronomical Observatories A Dedicated Place to Observe the Skies Ancient observers of the night sky were able to look at the heavens without much atmospheric disturbance, bar unfavorable meteorological conditions and naturally created hindrances. The skies, although not totally favorable, must have offered a great deal more than sites in present day, better than average viewing conditions, with a clearer, more clinical, and crisper appearance, with pollution and in particular light pollution being things of the future. Those very same skies that were so crystal clear, allowing the human eye to probably gain an extra portion of a magnitude when observing, are, barring dark sky reserves, very much in the minority today. The International Dark-Sky Association (IDA) has been striving to restrict the inroads made by artificial pollution, with the purpose of preserving the dark sky and promoting astronomy. Dark sky reserves are protected areas that offer exceptionally clear night skies and that are protected from human encroachment. There are six types of designations that categorize how the IDA has drawn a line in the sand to shield and protect the skies, and as of May 2019, there are over 115 certified sites in the world. As science has moved on, it became more and more apparent that the best way to study the sky was to go beyond our own personal protection barrier, which is the atmosphere. Humankind’s endeavor to push onwards would see the advent of a space telescope and subsequently better, more powerful instruments to follow. A new dawn was emerging where an instrument located in outer space could observe without the problems faced by ground-based observations of light pollution and distortion of electromagnetic radiation (scintillation). Furthermore, ultraviolet frequencies, X-rays, and gamma rays that are blocked by Earth’s atmosphere would finally have that necessary barrier removed, and a whole new world of space exploration would allow us to peek further into the depths of space. But before we look at these revolutionary © Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_10

163

164

10.  Astronomical Observatories

changes in observing, let’s look at what scientists were able to see from Earth’s surface at dark sky locations.

Ground-Based Observatories Optical observatories have a long and distinguished history, and before the progression of observations made from space, pioneered many aspects of astronomy without which we would not have been prepared to further push back the boundaries with the likes of the Hubble Space Telescope and others. The predecessors of astronomical observatories were monolithic structures that tracked the positions of the Sun, Moon, planets, and other celestial bodies chiefly for timekeeping or calendrical purposes. Nevertheless, historians would probably argue that whereas the primary purpose was for such affairs, that does not detract from the fact that many early civilizations had a far greater understanding of the universe around them than they are often given credit for.

Stonehenge One such structure is that of Stonehenge, constructed in England over the period from 3000 to 1520 b. c. Situated in Wiltshire, England, Stonehenge consists of a ring of standing stones, with each stone standing around 4 m high, 2.1 m wide, and weighing around 25 tons. The stones are set within earthworks in the middle of the densest area of complex Neolithic and Bronze Age monuments in England, including several hundred burial mounds. The construction parallels a timeline with the astrologer-priests in Babylonia, who observed the motions of the Sun, Moon, and planets atop terraced towers known as ziggurats. Although documentation exists to confirm this, no evidence has been found of any astronomical instruments that may have been used. The Stonehenge timeline also parallels the Mayan people of the Yucatan Peninsula in Mexico, who carried out the same practice as the astrologer-priests, conducting their observations at El Caracol, a dome-shaped structure somewhat resembling a modern optical observatory. However, as with the Babylonian observers, no evidence has been found of any scientific instrumentation used, even of a rudimentary nature. Added to UNESCO’s list of World Heritage Sites in 1986, Stonehenge and its purpose remain the subject of much debate,

Ground-Based Observatories

165

with even the actual construction techniques used giving little away. However, a general consensus here, and probably the most accepted theory of how the stones were transported to the site, would seem to point towards prehistoric people moving the megaliths by creating a track of logs upon which the large stones were rolled. A challenge to this notion suggests a type of sleigh running on a track greased by animal fat. As for Stonehenge’s purpose, many theories have been put forward as to its function – astronomical observatory and calendar being a widely accepted interpretation of the construction. British archaeologist Geoffrey John Wainwright (1937–2017) suggested Stonehenge was more of a place of healing, the primeval equivalent to Lourdes, a small town in the foothills of the Pyrenees, famed for its water and one of the world’s most important sites of pilgrimage and religious tourism. However, British archaeologist Professor Mike Parker Pearson (born 1957) of Sheffield University begs to differ, suggesting that Stonehenge was part of a ritual landscape, an extensive archaeological tract seemingly dedicated to ceremonial purposes in the Neolithic and early Bronze Ages (c. 3500–1800 b. c.). There is no arguing, though, that the site is aligned in the direction of the sunrise of the summer solstice and the sunset of the winter solstice, most notably supported in the work of British-­ born American astronomer Gerald Stanley Hawkins (1928–2003). Hawkins was professor and chair of the astronomy department at Boston University, and credited with much work conducted in the field of archeoastronomy, discovering that apart from the known and accepted two alignments, there were in fact dozens. Using the Harvard-Smithsonian IBM computer for his research, which used aspects of the stones in relation to how the night sky would have appeared in 1500 b. c., 13 solar and 11 lunar correlations were found. With no mention of any astronomical hardware being used by the Babylonians or Mayans, perhaps the first observatory that actually utilized instruments for accurately measuring the positions of the celestial objects was one built about 150 b. c. on the island of Rhodes, by the greatest of the pre-Christian astronomers, Hipparchus of Nicaea (c.190–120 b. c.), known to have been a working astronomer at least from 162 to 127 b. c. At the observatory, he discovered precession of the equinoxes, developed the magnitude system, and observed the appearance of a new star. Instrumentation used would have been simple, such as a gnomon, the astrolabe, and the armillary sphere. Hipparchus is credited with the invention or improvement of several astronomical instruments that were used for a long time for naked-eye observations.

166

10.  Astronomical Observatories

Wurdi Youang It is interesting to note that despite the international recognition of Stonehenge, there are several such sites, probably lesser known, that pre-date the stones in England. Along with two sites in Ireland, Loughcrew, and Newgrange, as well as one in Armenia, Zorats Karer, there is Wurdi Youang, an aboriginal stone arrangement at Mount Rothwell, near Little River, Victoria. Located to the northeast of the You Yangs hills, between Bacchus Marsh and Werribee, the arrangement, which is comprised of around 100 basalt stones, may well have been ceremonial in nature, as there are many other stone arrangements of a similar nature in the southeast of Australia. The stones range from small to waist-high rocks, arranged in a diamond shape that is about 50 m wide. However, research suggests that a series of stones located to the west of the arrangement’s western apex mark the positions of the setting Sun at the equinoxes and solstices. Estimated to be potentially as old as 11,000 years (based on carbon dating of nearby sites), a survey conducted at Wurdi Youang shows that the suggested alignments are accurate to within just a few degrees. In addition to the information gathered – which, if accurate, would make Wurdi Youang the world’s oldest astronomical site – the straight side of the stone arrangement, which diverges from its eastern apex, also indicates the setting position of the Sun at the solstices to within a few degrees, and at the equinoxes the Sun sets over three prominent stones at the apex. If the dating of Wurdi Youang is accurate, it would also pre-date the Egyptian pyramids. The stones in the arrangement also reflect the surrounding landscape, with the rocks matching three mountains nearby if an observer stands in certain positions. Although often not recognized, sites such as Wurdi Youang show a sophisticated understanding of the universe and science held by aboriginal people. Although much of this knowledge was dismissed by colonizers in Australia, a growing number of aboriginal people are reclaiming and reviving this past knowledge. In turn, this would suggest a longstanding knowledge of astronomy held by the aboriginal people. The area where Wurdi Youang is situated is inhabited by the Wathaurong people, an indigenous Australian tribe, part of the Kulin Alliance, made up of five indigenous tribes in south central Victoria. The Wathaurong people have inhabited the area for over 25,000 years, and the tribe elders are uncertain of the pur-

Ground-Based Observatories

167

pose behind the stone arrangement. This is mainly due to the fragmenting of information following the banning by missionaries in the area of the traditional language, customs, and ceremonies. However, it is understood that the land has been maintained by the same family since early colonial times, which would eliminate any European origin.

Goseck Circle Possibly the oldest and best of known of circular enclosures is that of the Goseck Circle, situated in the Byrgenlandkreis district of Germany. The site was discovered in 1991 by pilot and keen archaeologist Otto Braasch (born 1936) on an aerial survey map, one of many surveys conducted by Braasch who, over a period of some 25 years, has explored European heritage sites from the air, taking aerial photographs of structures and surrounding landscapes. On this one particular survey over the undiscovered Goseck Circle, Braasch captured circular edges under a wheat field, the cropmarks being easy to spot during a season of drought, and despite the site being in an advanced state of decay, its discovery at least gave archaeologists and those who were to preserve the site a chance to attempt to stop the erosion. The construction dates to approximately the forty-ninth century b. c., and it seems to have remained in use until about the forty-seventh century b. c. The circle consists of a concentric ditch 75 m across and two palisade rings containing entrances in places aligned with sunrise and sunset on the winter solstice days and smaller entrances aligned with the summer solstice. The site has undergone reconstruction in order to present the Goseck ring as it would probably have looked soon after being initially built, with archaeologists and state officials rebuilding the wooden palisade of the circle using 1675 oak poles at a height of 2.5 m. In order to attempt to make the posts look as authentic as possible, woodworkers worked with hand tools. The absence of any buildings inside the enclosure has presented archaeologists with a puzzle, but it did seem to counter the argument that the Goseck Circle was used as a fortification of some type. Perhaps one of the best preserved and extensively investigated structures, the site mirrors other constructions and pottery fragment finds of the same era at enclosures in Elbe and the Danube region, all of which show similar solstice alignments. All told, across the region, the era would reflect a traditional phase

168

10.  Astronomical Observatories

between Neolithic linear pottery and Stroke-ornamented ware cultures. The linear pottery culture is considered a major archaeological horizon of the European Neolithic era, evolving as a successor into the Stroke-ornamented ware culture, or STK, after the manner in which their pottery was decorated. Sites situated in the Czech Republic, Austria, and Croatia also dictate the Goseck Circle is not one of a kind, but in terms of being the most well-­ preserved, there is no finer example. The debate about the Goseck Circle’s astronomical credentials remains, with some archaeologists likening the site to Stonehenge, with wood replacing stone – labeling it with the unofficial stamp of Goseck Henge or the German Stonehenge, with another speculatively tangible parallel placing Stonehenge and the Goseck Circle on the same latitude! At the center of the debate is whether or not the site was used to monitor the Sun throughout the year or only on specific notable days, and thus whether to call the Goseck Circle a “solar observatory” or not, as some of the marketing material suggests. Archaeologist Ralf Schwarz suggests the structures at the site allowed coordinating an easily judged lunar calendar with the more demanding measurements of a solar calendar using the calendar calculations. Others claim the Sun and its annual calendar played a key role in the rituals performed at the site, with animal and human bones found, along with the pottery that had been unearthed. Thanks to the aerial surveys of enthusiasts such as Braasch, many other ditches and potential sites have been photographed through aerial surveys, but only a fraction, some 10%, have been inspected. The Goseck Circle is open to the public and forms an important link in a chain of “sky way” attractions across Europe that is related to the study of how astronomy was practiced in ancient times.

Kokino Situated in the Republic of North Macedonia, Kokino is a Bronze Age archaeological site approximately 30 km from the town of Kumanovo, about 6 km from the Serbian border. It was discovered in 2001 at a place called Tatic’s Stone near the village of Kokino by archaeologist and director of the museum at Kumanovo, Jovica Stankovski, along with Gorje Cenev. The two subsequently published a claim that the site contains a megalithic observatory and a section used for sacred rites.

Ground-Based Observatories

169

Built on a mountaintop 1013 m above sea level, the site stands upon a neo-volcanic plate made of andesite rocks. The mountain was later dubbed a “holy mountain” following the discovery of not only the remains of fractured ceramic vessels, molds for bronze and jewelry, but the fragments of other vessels filled with offerings. Aside from these finds, there are four impressive stone thrones there facing east towards the horizon. After measurements were taken by local physicists, it was claimed that not only was Tactic’s Stone a sacred site but it should also be recognized as a megalithic observatory. Accompanying the four stone thrones are seven more markers shaped from vertical standing rocks nearby. These markers indicate the rising positions of the Sun on the summer and winter solstices, and on the spring and autumn equinoxes. Next to the markers for the solstice of the Sun there are markers that were used for measuring the movements and phases of the Moon. All of the construction was designed in such a way so that on an exact day the rays from the Sun would pass through the marker and light up one of the thrones! With some speculation, it has been suggested that on special event days, a great fire would have burned behind the thrones on the mountaintop, a fire so large in nature that it could have easily been seen by all inhabitants of the surrounding areas, up to 30 km distant. One can draw parallels from Kokino to Stonehenge and the Cambodian temples, with regard to being considered as lunar calendars that show phases of the Moon, and even in some cases the 19-year eclipse cycle.

Cheomseongdae One can also not dismiss from the arena of ancient prototype observatories (akin to a private observational post) an astronomical observatory in Gyeongju, South Korea. Cheomseongdae is the oldest surviving astronomical observatory in Asia, constructed in the seventh century in the kingdom of Silla, which along with Baekje and Goguryeo formed the Three Kingdoms of Korea. Cheomseongdae, which means “star-gazing tower” in Korean, was built during the second year of the reign of Queen Seondeok (c. 595/610–647), the 27th Silla monarch, as an aid to the farming community. As a further aid, the queen also announced a whole year of tax exemption for the peasants and reduced taxes for the middle class!

170

10.  Astronomical Observatories

Cheomseongdae stands 9.17 m high and consists of three parts. Firstly, there is the base or stylobate, which in classical Greek architecture is the top step of the crepidoma, a multi-­level platform on which a structure is built. The column for the Cheomseongdae sits upon this base, cylindrical in construction, with a square top. Midway up the body stands a square window and entrance to the inside of the structure. The base of Cheomseongdae measures 5.7 m wide and is constructed from a layer of twelve rectangular stones, which may represent the 12 months of the year. From the base to the window, the tower is filled with earth and rubble, with access only to be gained by means of a ladder. The window itself separates the body of the column into twelve layers of stones both above and below, symbolizing the 12 months in a year and the twenty-four solar terms. Observational work would have been carried out from the top of the structure, likely using an armillary instrument – a model normally composed of rings showing positions and important circles on the celestial sphere. That said, the observatory, like those of the Chinese and Japanese of the same epoch, was not constructed purely for science, but also for soothsaying. Astrology would appear to be the prime motivation. The Cheomseongdae, which has remained unchanged in appearance for over 1300 years, in construction terms resembles the methodology and style used in the Bunhwangsa temple in Gyeongju, built in 634 under the rule of Queen Seondeok. In its original format, the Bunhwangsa temple covered several acres and was one of four main temples of the Silla kingdom. According to Eun Hen Lee, a historian of science at Yonsei University in Seoul, it is possible that just as the Chinese ruling elite were interested in the movements of bodies in the sky for guidance on political and social matters, the same could be applied to Queen Seondeok. Interestingly, records document that the Cheomseongdae observatory sighted at least 29 comets! Research would seem to suggest that Queen Seondeok had the intention that Cheomseongdae be built to share the knowledge of astronomy. Some research suggests that the shape of the structure is in line with the Chinese theory of round-heaven, square-Earth, and that the layers of stones themselves are meant to represent Queen Seondeok. Despite a slight listing of the Cheomseongdae to the northeast, the structure remains standing. The National Research Institute of Cultural Heritage in Korea is carrying out regular inspections and working closely with the Gyeongju municipal government, which

Ground-Based Observatories

171

oversees the site’s management and preservation. It’s inspiring that to note that Queen Seondeok saw fit to have such a curious tower constructed, and while the founding reason behind its construction may not have been entirely scientific in nature, the fact that it was built with the heavens as a central motivation speaks well of her intentions. It is interesting to note the Korean participation in the world of astronomical affairs, which on an international scale is somewhat overshadowed by the Japanese and most certainly by the Chinese. Korean records exist of three of the six observed supernovae in our galaxy in the last two millennia, a. d. 1054, 1572, and 1604, with the 1604 outburst observed for several months by the Koreans. However, and quite interestingly, according Lee, no records exist of SN 1006 in Korea. Indeed, the very origins of Korean ancient astronomy date back to the prehistoric era. Astronomical signs in the prehistoric age are star-like cup marks carved on cover stones of dolmens. It is evident that ancient Korean kingdoms established their own bureaus of astronomy, built observatories, and employed administrators designed to observe astronomical phenomena. Dating back to the first century b. c., over 20,000 extensive historical records and relics have passed down from generation to generation. One such piece of outstanding work to come from Korea is the Joseon dynasty’s astronomical chart. Engraved with 1467 stars, it is the second oldest surviving chart of its nature in recorded history, proving the importance of international participation in how we have monitored, documented, and recorded the skies throughout history. Unlike Chinese charts, in which all the mapped stars are depicted as being the same size, the Korean chart clearly notes that the stars themselves are of different sizes. The chart, carved on a stone plate in the year 1395, reflect a general undertaking by kings and nobility of the time that astronomy was to be supported and encouraged. Yi Seong-gye, or the Taejo (1335–1408), who was the founder and king of the first Joseon dynasty, in 1392, needed a medium to prove that he had established a new dynasty with the mandate of heaven in order to consolidate its legitimacy and heighten pride as a strong and lawful monarch. Fortunately, at that time, a rubbed copy of a stone-carved astronomical chart was delivered to him. The stone carving, made in Goguryeo (37 b. c–a.d. 668), was known to have been submerged in the Taedong River and lost during the war that led to the eventual fall of the ancient kingdom.

172

10.  Astronomical Observatories

Taejo ordered his court astronomers, including neo-Confucian scholar Gwon Geun (1352–1409), to produce a new astronomical chart by supplementing the ancient version. After further observations of the skies to eliminate positional and other errors arising over seven centuries, the result was a far more detailed and precise chart containing not only the names of the stars and constellations but rich astronomical data. Produced on black stone measuring 48 inches in width, 83 inches in height and 5 inches in depth, aside from the 1467 stars visible from Korea, the engraving showed 264 constellations and their names, the ecliptic and equatorial lines, and 365 scales around. The map positioned the heavenly bodies in their natural order and in their respective celestial fields. The epoch of the stellar positions is estimated to be near the first century for the stars with declination less than 50 degrees, and to be near a. d.1395 for stars with declination higher than 50 degrees. The chart has more than three times as many constellations as Western astronomical charts produced during the same period, which have 88 constellations. The outermost circle measures 30 inches in diameter and has the North Star at the center along with the Sun’s ecliptic and the equator equidistant from the North Pole and South Pole. The chart delineates the movements of the five visible planets (Mercury, Venus, Saturn, Mars, and Jupiter) and subsequent seasonal divisions. The whereabouts of the astronomical charts remained unknown until the 1960s, when the original stone carving was found abandoned on the grounds of Changgyeong Palace in Seoul. A family needing a table for their picnic there happened to find a stone block under the eaves of the Myeongjeongjeon pavilion. While covering the rectangular stone with a cloth to place their food upon it, the family noticed the block was carved with strange patterns and numerous small dots. It was none other than one of the most priceless astronomical relics brought to light, just discarded in grass and trampled on by countless feet over half a century! During its time in use and before being discarded then luckily eventually recovered, numerous copies were printed and disseminated throughout the kingdom, until it was superseded by Western planispheres in the nineteenth century. The map is the 228th national treasure of South Korea, and is exhibited at the National Palace Museum in Seoul. One of the great figures to emerge from the Joseon dynasty was Korean scientist and astronomer Jang Yeong-sil (c.1390-

Ground-Based Observatories

173

post-1442). Yeong-sil was responsible for the construction of a number of brilliant astronomical instruments that serve as evidence of not only his own vast scientific knowledge but that of the Korean contributions internationally to the development of science as a whole. Despite his peasant upbringing, the talents of the aspiring scientist were identified by King Sejong the Great of Joseon (1397–1450), allowing him to work as a government official at the palace. In his time, Jang created five astronomical instruments and ten timekeeping instruments, including a celestial globe, sundial, and water clock. International cultures and societies evolve at different rates, with the first systematic observations in Islam reported to have taken place under the patronage of al-Mamun (786–833). As with many other private observatories from Damascus, one of the oldest continuously inhabited cities in the world, to Baghdad, in modern times second largest city in the Arab world, meridian degrees were measured, solar parameters established, and detailed observations of the Sun, Moon, and planets undertaken.

Gaocheng Astronomical Observatory In an era in which there was a shift from the so-called proto-­ observatories, those more akin to private observational posts such as Cheomseongdae, the construction of ‘true observatories’ had begun to develop, and specialized research institutes emerged. One such observatory is the Gaocheng astronomical observatory. Also known as the Dengfeng Observatory, the site has a long tradition of astronomical observations, dating from the time of the Western Zhou (c. 1045–771 b. c.), the first half of the Zhou dynasty of ancient China, up to the early Yuan dynasty, which ruled from 1273 to 1368, subsequently followed by the Ming dynasty. It is believed that Duke Wen of Zhou had erected at this place an observatory to observe the Sun, stemming from an interest in mathematics, astronomy, and astrology. According to the Zhoubi Suanjing – one of the oldest Chinese mathematical texts dedicated to astronomical observation and calculation (“Zhoubi” referring to the Zhou dynasty and “Suan Jing” to classic arithmetic) – the observatory took on the appearance of a sundial. During the Tang dynasty, astronomer, mathematician, and mechanical engineer Yi Xing (683–727) expanded on the idea, building 30 standardized gnomons (part of the sundial that casts the shadow), which were spread out over China to measure to the

174

10.  Astronomical Observatories

equation of time, dependent on the geographical location. Ten of these sites were aligned along the meridian to the east of Greenwich from central Asia down to Vietnam in order to determine the circumference of Earth and derivations from a perfect sphere, and one such observatory was at Gaecheng. In order to fulfil the scientific requests of the Tang court, Yi Xing had been placed in charge of a terrestrial survey, its purpose being multifarious but including accurately measuring the circumference of Earth. The early part of the Yang dynasty saw the building of the great observatory in 1276 on the order of Kublai Khan (1215–1294), who reigned from 1260 right up until his death in 1294. Used to observe the movements of the Sun, the stars, and record time, the calculations helped to produce the new Shoushi calendar (season-­ granting calendar) of 1281, which was meant to last for 364 years, the longest period a calendar would be used in Chinese history. Two notable names working at the observatory included Guo Shoujing (1231–1316) and Wang Yun (1235–1281). Built of bricks and stone, the observatory was instructed of two main parts: the body, and what was known as the shigui (the ruler used to measure the sky). The structure has a trapezoidal shape and is regarded as the oldest astronomical platform in China, and during its time played an important role because it was determined to be the ‘Earth core,’ which means the most central point on the surface of the planet. Indeed, positioned south of the Gaecheng Observatory, in the temple dedicated to Zhou Gong, a Shingui chart made by Yi Xing can be found, where, according to the Zhou Li (“Rites of Zhou”), it is the center of Earth! It is interesting to note that with regard to Zhou Gong, this particular accolade stems from the admiration shown by Chinese philosopher Confucius (551–479 b. c.) towards the Duke of Zhou. The admiration was so intense that he would dream of Zhou Gong; hence, the saying in chess to “play chess with Zhou Gong,” referring to being in a state of sleep or dreaming blissfully. The observatory became the first in a series of 27 observatories, so-called “observation stations,” built in the early Yang dynasty.

Uraniborg Observatory Uraniborg Observatory is credited by some scientists as being the first observatory to change the face of astronomy forever. It

Ground-Based Observatories

175

was a dedicated astronomical observatory and alchemy laboratory built on Hven, a small Swedish island situated between Zealand and Scania, Sweden, which was part of Denmark at the time. Established and operated by astronomer Tycho Brahe, the facility was built c.1576–1580 and was dedicated to Urania, the muse of astronomy, and named Uraniborg, or the Castle of Urania. From the ancient Greek, Urania means “heavenly” or “of heaven,” and it was the first custom-built observatory in modern Europe, though not the last to be built without a telescope as its primary instrument. Brahe himself laid the cornerstone to the observatory on August 8, 1576. Measuring just 7.5 sq. km, the island of Hven was the world’s premiere destination for scientists and philosophers in the sixteenth century, for here resided the most advanced research institution the world had ever seen. However, its beginning was completely non-scientific. Working under the patronage of King Frederick II of Denmark (1534–1588), Brahe had been dispatched abroad to find architects and engineers to produce the lavish and quite ambitious building projects that the king had envisaged. Brahe, on his return, made his own plans to settle in Basel, Switzerland, a city at the northwestern edge of the country near the river Rhine, located where the Swiss, French, and German borders meet. However, in a cunning plan to keep Brahe in Denmark, and to reward Brahe for his service, what could pass as a bribe was offered to the astronomer, in the form of an island as a place for him to conduct his studies in astronomy and chemistry, an offer that was seemingly too good to refuse. Uraniborg, which was completed in 1580, consisted of a square three-story building constructed mostly of red brick, approximately 15 m a side, and was extended to the north and south by a semi-circular tower on each of these walls. It was in these, on the middle floor, that the primary instruments were housed, such as sextants and quadrants, some of Brahe’s own design, some of which he had modified. The instruments were placed intermittently on purpose-built balconies along the towers. The construction was undertaken in the style of the Flemish Renaissance by the architect of the royal Danish court, Hans van Steenwinckel the Elder (1550–1601), and sculptor Johan Gregor van der Schardt (c.1530/1–c.1581), working in close cooperation with Brahe. A year later, in 1581, Brahe, who apparently found Uraniborg too small and too vulnerable, added to the construction with a smaller Stjernsborg (“star castle” in English, “castle of the

176

10.  Astronomical Observatories

stars” in Danish or Latin) being built on an adjacent site. Brahe’s Stjernsborg, which was constructed 80 m south of Uraniborg, was an underground observatory, with no buildings higher than ground-floor level. Stjernsborg consisted of five round towers with conical domes called crypts. The astronomical techniques used at both Uraniborg and Stjernsborg spread throughout Europe over the coming years. But sadly, with a change of ruler, the successor to Frederick II, Christian IV (1577–1648), affairs took a distinct turn for the worse. This was coupled with a decline in Brahe’s popularity and an outright dislike of Brahe by Christian IV, and resulted in the two highly respected structures being destroyed after Brahe’s death in 1601. However, from the ruins, which saw Brahe measure the positions of the stars and planets with unprecedented accuracy, the knowledge gained – including voluminous amounts of data – was bequeathed to Johannes Kepler, who published it and used the data as the basis for his famous three laws of planetary motion.

Paris Observatory The foremost astronomical observatory of France has its roots in the ambitions of French politician Jean-Baptiste Colbert (1619– 1683) who, while serving under King Louis XIV (1638–1715), had plans to extend France’s maritime power and international trade. With Louis XIV promoting its construction, and predating Royal Greenwich Observatory with its completion in 1671, 4 years before Royal Greenwich, Colbert’s vision was realized. Designed by architect Claude Parrault (1613–1688), best known for his participation in the design of the east façade of the Louvre in Paris, the building work at the observatory was further extended in 1730, 1810, 1834, 1850, and 1951. Italian optician and astronomer Giuseppe Campani (1635–1715), with Louis XIV ordering several long-focus lenses from him at the height of abilities, was considered the best maker of optical instruments of his time. Along with his brother, Matteo Campani-Alimenis, the two were experts in grinding and polishing lenses, especially for very long focal length aerial telescope objectives, which was what Louis XIV had commissioned. With these new lenses, astronomer and mathematician Giovanni Domenico Cassini (1625–1712) made some landmark discoveries in astronomy. Originally an astronomer at the Penzano Observatory, near Bologna, Italy, Cassini was made director at the

Ground-Based Observatories

177

Paris Observatory in 1671. He is also credited with introducing Indian astronomy into Europe, and made a staggering host of discoveries, including observing and publishing his observations of the surface markings on Mars, the determination of the rotation periods of Mars and Jupiter, and the joint discovery with Robert Hooke of the Great Red Spot on Jupiter (c. 1665). However, it is his work with regard to Saturn that he is perhaps most noted for. Firstly, there was the discovery of four of the satellites of Saturn. In what Cassini referred to as Sidera Lodoicea (the stars of Louis), he discovered Iapetus and Rhea in 1671, and Tethys and Dione in 1684. The name Sidera Lodoicea, intended to honor Louis XIV, was modeled on Sidera Medicea, “Medicean star,” the Latin name used by Galileo to name the four Galilean satellites of Jupiter, Io, Europa, Ganymede, and Callisto, in honor of the Florentine house of Medici. Cassini had also noted that Iapetus, the third-largest satellite of Saturn, which he discovered during October 1671, was eluding him when attempting to sight it on the eastern side of the planet. Discovered on the western side, Cassini had waited for it to emerge on the eastern side, but had failed to rediscover its presence as predicted. After a second attempt to sight Iapetus failed, Cassini finally observed the satellite on the eastern side in 1705 while using an improved telescope, finding that Iapetus had lost two magnitudes on the eastern side. Although such a puzzle may well have stumped others, Cassini correctly surmised that Iapetus has a bright hemisphere and a dark hemisphere, and that it was tidally locked, a term also referred to as gravitational locking or captured rotation, meaning that the satellite always kept the same face towards the planet. This means that the bright hemisphere is visible from Earth when Iapetus is on the western side of Saturn, and that the dark hemisphere is visible when Iapetus is on the eastern side. In his honor, the dark hemisphere was later named Cassini Regio, “Regio” being a term used in planetary geology for a large area that is strongly differentiated in color or albedo from its surroundings. The conclusions reached by Cassini were later confirmed by much larger and more powerful telescopes. Many theories exist as to the curious and dramatic differences in coloration between Cassini Regio, the dark region, and the bright region, which in turn is divided up into Roncevaux Terra north of the equator and Saragossa Terra to the south. The name Roncevaux Terra is after the Battle of Roncevaux Pass in 778, subject of the epic French poem Chanson de Roland,

178

10.  Astronomical Observatories

“The Song of Roland” – interestingly, the oldest surviving major work of French literature. Roland was a Frankish military leader under Charlemagne, or Charles the Great (742–814). Saragossa Terra (“Terra” referring to extensive landmasses) is also linked with the same poem. There are possible references here to either a character, King Marsile, said to be the last of the Spaniards to make a stand against the Franks, or the town of Marsilion, eventually taken by the French. Alternatively, it may simply relate to Saragossa, or Zaragoza in Spanish, the battle of which took place during the War of Spanish Succession. It is astonishing to think that many years later, on September 10, 2007, an orbiter bearing Cassini’s name would pass Iapetus at a distance of just 1227 km, taking close-up images of the very surface that gave some differing appearances when first viewed. Another demonstration of how humankind, which once recorded the spectacle through an optical aid alone, was to later document and image such phenomena by totally different means, hundreds of years later, and yet both are viewing the very same object. Two extremes of recording the same object – testimony to the man Cassini and craft Cassini. The incredible list of achievements by Cassini also includes the famous Cassini division, discovered in 1675 from the Paris Observatory. The Cassini division is a region measuring 4700 km in width that sits between Saturn’s A ring and B ring, a gap almost as wide as the planet Mercury. The world’s first national almanac was published by the Paris observatory in 1679. The Connaissance des temps (“Knowledge of Time”) is the oldest such publication in the world, published without interruption since 1679. Its volumes have two parts, a section of ephemerides, containing various tables, and articles contributed on various deeper topics by famous astronomers, making the publication a widely sought-after piece of literature. The 1679 edition used eclipses in Jupiter’s satellites to aid seafarers in establishing their longitude. The 33-inch Meudon great refractor was used at the observatory, in conjunction with observations made by E. M. Antoniadi (1870–1944), to help disprove the existence of canals on the surface of Mars. The Meuden was a double telescope initially completed in 1891, with the secondary having a 24-inch aperture lens for photography, making it one of the largest active ‘scopes in Europe at the time.

Ground-Based Observatories

179

Antoniadi was a keen observer of Mars, making a name for himself with the observational data produced. Initially, Antoniadi supported the theory of Martian canals, but after work conducted at the Paris Observatory, he reversed his backing of the notion, concluding that the canals were simply an optical illusion. His visual contribution, which was made during the 1909 opposition of the planet, was supported by photographs taken by the then newly constructed Baillaud dome at the Pic du Midi Observatory. The images taken here from the top of the French Pyrenees were instrumental in placing the Martian canal, or Martian construction work theory, firmly out of favor. Despite spectroscopic analysis, which came to the fore during this time clearly indicating that no water was present on Mars, the idea was still defended by some, most notably American science writer Waldemar Kaempffert (1877–1956). Along with making the first but sadly flawed map of Mercury, with his incorrect assumption that Mercury had a synchronous orbit, Antoniadi is also famed with creating the Antoniadi scale of seeing, which incorporates a five-point weather condition-related system. In 1913, the Paris Observatory, using the Eiffel Tower as an antenna, exchanged sustained radio signals with the U. S. Naval Observatory in Arlington, Virginia, to determine the exact difference of longitude between the two institutions. This was not the first time the Eiffel Tower, originally built for an exhibition in celebration of the French Revolution, was used as a broadcasting mast, the first signals being transmitted on November 5, 1898. French scientific instrument maker Eugene Adrien Ducretet (1844–1915) caused quite a stir when he successfully transmitted the signals from the third floor of the Eiffel Tower to the Pantheon, some 4 km away.

Royal Greenwich Observatory Commissioned for navigational purposes in 1675 by King Charles II (1630–1685), the foundation stone at the Royal Greenwich Observatory, whose site was chosen by Sir Christopher Wren (1632–1723), was laid on August 10. Alongside its navigational duties, its primary contributions were in practical astronomy, star positions and almanac publication, plus timekeeping. The observatory began publishing The Nautical Almanac in 1766, with data for 1767, which established the longitude of Greenwich as

180

10.  Astronomical Observatories

a baseline for time calculations. The almanac’s popularity among navigators led in part to the adoption in 1884 of the Greenwich Meridian as Earth’s prime meridian and a starting point for international time zones. At the time of the construction of the observatory, King Charles II created the post of Astronomer Royal, the first of which was John Flamsteed (1646–1719), who laid the foundation stone at the observatory. During his scientific career, Flamsteed prepared a 3000-star catalog named the Catalogus Britannicus, and a star atlas called Altas Coelestis, both of which were published posthumously. Flamsteed is also responsible for making the first recorded observations of Uranus, although he mistakenly cataloged it as a new star in the constellation of Taurus, documenting the planet as “34 Tauri.” The first recording of “34 Tauri” was made in December 1690, making it the earliest recorded sighting of Uranus. Ironically, Flamsteed also cataloged a star named 3 Cassiopeia, but this particular record, unlike that of “34 Tauri,” remained uncorroborated. American astronomical historian William Ashworth proposed that what Flamsteed had actually seen was the most recent supernova of the time, an event that would leave as its remnant the strongest radio source outside of the Solar System, known in the third Cambridge catalog as 3C 461, commonly called Cassiopeia A. The supernova occurred approximately 11,000 light years away within the Milky Way. It is estimated that light from the stellar explosion first reached Earth approximately 300 years ago. Since Cassiopeia A is circumpolar from the mid-northern latitudes, this is probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth. However, it remains possible that it was indeed recorded as a sixth magnitude star by Flamsteed on August 16, 1680. The observatory was gradually transferred from Greenwich to Herstmonceux in Sussex from 1948 to 1957, in a search for clearer skies, subsequently moved to the Institute for Astronomy at the University of Cambridge in 1990. A controversial cost-cutting measure announced by the Particle Physics and Astronomy Research Council in 1997 brought about the shutdown of the observatory in 1998. The institution’s equipment and operations, including the William Herschel Telescope and other instruments located on La Palma in the Canary Islands, were consolidated under the UK Astronomy Technology Center, headquartered at the Royal Observatory in Edinburgh, Scotland. Some of the instruments were returned to the Old Royal Observatory, which was renamed the Royal Observatory Greenwich.

Radio Astronomy

181

Radio Astronomy Radio astronomy was born in the early 1930s, when American physicist and radio engineer Karl Guthe Jansky (1905–1950) first discovered radio waves emanating from the Milky Way. Jansky, working for the Bell Laboratories, was trying to determine the origin of a source of noise that was showing up in receivers operating in the 20 MHz region of the radio spectrum. Jansky built a steerable antenna and began searching for the source of the noise by taking directional measurements. To Jansky’s surprise, he discovered that the noise was from a source that was extraterrestrial. Jansky’s findings led him to publish his discoveries, but despite expecting positive and encouraging feedback that may have led to a much more in-depth undertaking to pinpoint the source, the astronomical community in general dismissed the findings as either irrelevant or just curious at best. However, fortunately, not all of the community was dismissive of Jansky’s discoveries, with electronics engineer Grote Reber (1911–2002) reading through the published work. Reber speculated that the signals Jansky was hearing were in fact of thermal origin, caused by very hot objects, and as such should be easier to detect at higher frequencies. Since the original work was conducted at 20 MHz (about 15-m wavelength), and with a beam width of about 25 degrees, Reber, a keen amateur radio enthusiast, wanted to narrow the effective beam width in order to refine the detail. In order to achieve this, Reber reasoned that he would need to build a receiver and antenna considerably more advanced than that of Jansky’s. In the summer of 1937, Reber, using his own resources, funding, and boundless enthusiasm, built the first parabolic reflector radio telescope. The telescope was massive, measuring 9.5 m in diameter, focusing to a radio receiver 8 m above the dish. As Reber built the telescope without any financial help or construction assistance, this was a fine achievement. The entire assembly was built on a tilting stand, allowing it to be pointed in various directions, though not turned. Work on the telescope was finally completed in September 1937. As the term “radio telescope” hadn’t even been coined yet, we can certainly attribute the first building of such a ‘scope to Reber. For nearly a decade after the telescope’s construction in 1937, Reber was the world’s only radio astronomer. However, and rather sadly, Reber was unable to prove his hypothesis with his first receiver, which operated at 3300 MHz, as the receiver failed to detect signals from outer space. Undeterred,

182

10.  Astronomical Observatories

he built another receiver, which operated on 900 MHz; this, too, failed to bring any results. For Reber, it was a case of third time lucky, with 160 MHz proving successful in 1938, confirming what Jansky had discovered. Reber went on to detail the first radio map of the galactic plane, completing a radiofrequency sky map in 1941, making further observations and extending the map in 1943. As well as his published work, which included “Cosmic Static,” Reber’s data was published as contour maps showing the brightness of the sky in radio wavelengths, also revealing the existence of radio sources in Cygnus A and Cassiopeia A for the first time. It was the search for static and noise that led to the development of the radio telescope, and the introduction and future expanding of this particular branch of astronomy, making its part in the science as important as the observational branch. Certain astronomical phenomena have sound characteristics, with, across the genre of radio astronomy, a mixture of signal properties such as frequency, phase, amplitude, and in some cases, repetitive patterns. It is possible from these signals to produce a mathematically assembled “radio picture” of these cosmic objects, allowing for both the potential to study an object through a telescope and build a pictorial representation of the object from its sound. As you can imagine, a great deal more work goes into the production of an image from a radio telescope than one that can be virtually instant through optical means. Each little point in the image is stored in computer memory as an individual pixel. For a single-dish telescope, such as the Parkes 18-m dish stationed in New South Wales, Australia, the telescope scans across an object and receives radio waves from each little point across the object being studied. Some of the points in the object emit more energy than others. Each pixel is individually stored with the computer, converting this information into a series of numbers. If radio waves are weak at any particular position on the object, a small number would be recorded in the pixel, with no radio wave received registering a zero in the pixel. A higher concentration of radio waves would obviously reflect a higher number in the pixel, with astronomers then applying different colors to distinguish different areas of intensity, gradually building up an overall picture of the object. The process can take hours, perhaps days, with the final data process possibly running into weeks, dependent on the object and how many pixels and associated colors it ultimately commands. Extraterrestrial radio signals are extremely weak, so weak that, as an example, if all the signal energy ever received from all

Radio Astronomy

183

the radio telescopes ever built around the world were combined (signal sources from objects other than the Sun), there would not be the collective total energy output to melt a solitary snowflake. The aim of the radio telescope is to capture a wide area of signals and focus them into a much smaller field, much in the same way that a reflecting optical telescope operates, the term “radio optics” referring to this similarity. Since the term “light” really means electromagnetic radiation, all the same basic equations and formula, theories, and principles can be applied to radio, infrared, and visible light. The difference is that optical telescopes operate at much higher frequencies and microscopic wavelengths, while radio telescopes work at significantly lower frequencies and longer wavelengths. Resolution in optical astronomy can be paralleled by beam width in radio astronomy. Essentially a very sensitive radio receiver and basically an energy measuring device, the large antennas seen on most telescopes are built that large in order to make their “beam patterns” as small as possible. The beam pattern is the two-dimensional areas as projected upon the celestial sphere, to which the telescope will be sensitive. A small beam pattern endows the telescope with the ability to resolve the level of signals arriving from regions separated only by a small angular distance. Multiple antennas are sometimes combined as “arrays” to enhance resolution. Widely separated antennas may have their signals combined in an “interferometer” arrangement, where resolutions can be obtained that surpass those of optical telescopes. Applicable in both optical and radio astronomy, this array of separate telescopes, mirror segments, or radio telescope antennas work together as a single telescope to provide higher resolution images of astronomical objects. Although used in optical astronomy, the widest use of astronomical interferometer is in radio astronomy, in which signals from radio telescopes are combined. A mathematical signal-processing technique known as aperture synthesis is used to combine the separate signals to create highresolution images. At the shorter wavelengths used in optical and infrared astronomy, it is more difficult to combine the light from separate telescopes, because that light must be kept coherent within a fraction of wavelengths over optical paths, requiring very precise optics. At optical frequencies (blue-green light 600,000 GHz or wavelength of .0005 mm), a 1-m perfect mirror will have a beam width of approximately .00003 degrees. The same mirror operating at radio frequencies (30 GHz, for example, with a wavelength of 1 cm), will have a beam of approximately 6 degrees.

184

10.  Astronomical Observatories

Observatories Above Earth Despite the formidable array of ground-based observatories that combine the latest cutting-edge technology to continue the evolution of how we record the night sky, the introduction of manned missions and then deep sky probes added greatly to our knowledge of our universe. Each successive instrument packed in more and more computing power by the square inch, and the advent of one particular piece of equipment revolutionized the documenting of our universe, the Hubble Space Telescope (HST). Launched into orbit on April 24, 1990, at 12:33: 51 UTC from Kennedy Space Center the Hubble Space Telescope was to enter into service on May 20, 1990, with its low Earth orbit (LEO), maintaining an altitude of 2000 km (approximately one-­third of the radius of Earth). The International Space Station (ISS) also conducts operations in LEO and, to date, all crewed space stations as well as the majority of satellites have been deployed here (Fig.10.1).

Fig. 10.1.  Hubble Space Telescope. (Courtesy of NASA.)

Observatories Above Earth

185

The altitude record for human spaceflights in LEO was held by Gemini 11, with an apogee of 1374.1 km, with Apollo 8 the first mission to carry humans beyond LEO on December 21–27, 1968. Astronauts Charles “Pete” Conrad, Jr. (1930–1999) and Richard Francis Gordon, Jr. (1929–2017) flew Gemini 11, Conrad, becoming the third man walk on the Moon during the Apollo 12 mission, which was the sixth manned flight in the Apollo program and the second in that program to land on the Moon. Launched on November 14, 1969, from Kennedy Space Center, four months after Apollo 11, Conrad walked on the lunar surface during November 19–20. Gordon remains only one of 24 people to have flown to the Moon. Apollo 8 was the second manned spaceflight mission flown in the Apollo space program. Launched on December 21, 1968, it became the first manned spacecraft to leave LEO, reach the Moon, orbit it, and return home. Unfortunately, LEO itself has become quite a crowded area, with plenty of our own space debris, aside from the cosmic debris, which causes a significant threat to humanity. Because of the frequency of object launches, a growing concern has developed over the possibility of orbital collisions, which can be dangerous or even deadly. With literally thousands of objects in orbit, and with many more countries involved than ever before, collisions creating a so-called domino effect are not just paper-based probability theories but a real threat, subsequently earning the label of the Kessler syndrome. We know the domino effect to be a chain reaction produced when one event sets off a chain of similar events; the Kessler syndrome (also called collisional cascading), proposed by NASA scientist Donald J. Kessler (born 1940), is a scenario in which the density of objects in LEO is high enough that collisions between objects could cause a cascade where each collision generates space debris that in turn generates the possibility of further collisions. Kessler first proposed the idea in 1978, in an academic paper titled “Collision Frequency of Artificial Satellites: The Creation of a Debris Belt.” The paper established Kessler as an authority on the subject. The HST, named after American astronomer Edwin Hubble, ranks alongside NASA’s great observatories, including the Compton Gamma Ray Observatory, the Chandra X-Ray Observatory, and the Spitzer Space Telescope. Hubble is regarded as one of the most important astronomers of all time for his work in the fields of extragalactic astronomy and observational cosmology (Fig. 10.2).

186

10.  Astronomical Observatories

Fig. 10.2.  Deployment of the Compton Gamma Ray Observatory. (Courtesy of NASA)

The HST was not the first space telescope; that accolade belongs to the Orbiting Astronomical Observatory 2 (OAO-2), which was nicknamed “Stargazer.” That said, we have to delve deeper into history to find the very roots of the concept of a space telescope. The notion of placing a telescope in space to make observations outside of Earth’s atmosphere can be traced back to Austro-­ Hungarian-­born German physicist and engineer Hermann Oberth (1894–1989). Oberth is considered to be one of the founding fathers of rocketry and astronautics and is credited with first suggesting that a telescope could be launched into orbit to help overcome the distortions caused by the atmosphere. As rocket launchings became more commonplace, the idea became feasible, and in 1969, approval was given for the launch of a Large Space Telescope (later to be renamed the Hubble Space Telescope). Its development would take longer than preparing for a trip to the Moon. Along with the European Space Agency (ESA), NASA moved forward on the plan that would eventually become Hubble.

Observatories Above Earth

187

The U. S. Congress approved funding for the telescope in 1977, along with the funding of the space shuttle program, providing a new craft that together with the telescope would dovetail to provide an instrument orbiting above Earth that could be maintained and serviced at regular intervals. German astronomers Wilhelm Beer (1797–1850) and Johann Heinrich Madler (1794–1874) discussed the advantages of not only having a telescope in space but more specifically one based on the Moon. Beer and Madler produced the first exact map of the Moon entitled Mappa Selenographica in 1834–1836, publishing a description of the Moon in Der Mond nach seinen kosmischen und individuellen Verhaltnissen, “The Moon according to its cosmic and individual circumstances,” in 1837. Many decades later, both these publications remained at the forefront of the then latest understanding of the Moon. Beer and Madler came to the conclusions that the lunar features do not change and that the Moon has no atmosphere or water. It wasn’t until 1868 that fellow German astronomer Johann Friedrich Julius Schmidt (1825–1884) published a map that superseded that of Beer and Madler in its accuracy and detail. Schmidt spent many years studying the Moon before eventually producing the map, and such was his talent and emerging authority on lunar detail that his revelation that the Linne Crater had considerably changed its appearance was taken very seriously. Along with his own drawings of the Moon and earlier work on the lunar surface produced by German astronomer Johann Hieronymus Schroter (1745–1816), Schmidt stated that “at the time of oblique illumination [it] cannot at all be seen,” whereas at high illumination it was visible as a bright spot. Linne is a small lunar impact crater located in the western Mare Serenitatis, named after Swedish botanist Carl von Linne (1707–1778). Schmidt claimed that the crater had changed from its normal appearance of a somewhat deep crater into simply a mere white patch. The idea was later dismissed as a transient lunar phenomenon (TLP), a term created by amateur astronomer and broadcaster Sir Patrick Moore (1923–2012) in his co-authorship of NASA Technical Report R-277, The Chronological Catalog of Reported Lunar Events, which was published in 1968. A TLP is a short-lived light, color, or change in the appearance of the Moon, claims of which date back at least 1000 years. Aside from such events as outgassing, from which the lunar atmosphere

188

10.  Astronomical Observatories

probably originates as warmer material below the surface of the Moon escapes, and impact cratering, which are direct strikes on the lunar surface from cosmic debris, the Moon does not alter its appearance. However, the genuine misinterpretation of lunar phenomenon is not consigned to that of Schmidt, with Sir William Herschel on the night of April 19, 1787, reporting three red, glowing spots on the dark part of the Moon. Along with Houston radioing the Apollo 11 mission to observe and determine a bright glow on the Moon’s surface that had been observed by astronomers in West Germany, many other sightings are documented. In an effort to categorize such phenomena, Transient Lunar Phenomena have been divided into four classes: • • • •

Outgassing Impact events Electrostatic phenomena Unfavorable observation conditions.

With the use of Beer’s private observatory in Tiergarten, Berlin, which housed a 9.5-m refractor built by Bavarian physicist and lens maker Joseph Ritter von Fraunhofer (1787–1826), Beer and Madler also created the first globe of the planet Mars in 1830, and 10 years later, in 1840, produced a map with an incredibly accurate calculation of the rotation period of the Martian world. They calculated the period with an accuracy of just 1.1 s shy of today’s accepted rotation, 24 h, 39 min, and 35 s if gauged by a solar day, or 24 h, 37 min and 22 s for the sidereal day. Mars rotates about 40 min slower than Earth. Fraunhofer himself discovered and studied the absorption lines in the spectrum of the Sun, now known as Fraunhofer lines. Craters on both the Moon and Mars, along with an asteroid, have been named in Beer’s honor, with a crater on the Moon and Mars named after Madler, who is regarded as one of the great and eminent astronomers of the nineteenth century. However, although Beer and Madler proposed a lunar-based telescope, the idea of a telescope in space was first suggested by American theoretical physicist and astronomer Lyman Strong Spitzer, Jr. (1914–1997) in 1946, 11 years before the Soviet Union launched the first satellite, Sputnik 1, on October 4, 1957. Spitzer was an early proponent of space optical astronomy in general, and in particular of the project that eventually produced the Hubble Space Telescope. Spitzer’s proposal called for a large telescope that

Observatories Above Earth

189

would not be hindered by Earth’s atmosphere, and with lobbying through the 1960s and 1970s he would ultimately see such a vision being produced, in the form of the HST. Once known as the Space Infrared Telescope Facility (SIRTF), the Spitzer Space Telescope (SST) would later be renamed in his honor – a fitting tribute to the man who made major contributions in the areas of stellar dynamics, plasma physics, thermonuclear fusion, and space science. At a cost of $720 million, the SST was launched on August 25, 2003, from Cape Canaveral, its original mission duration being planned for 5 years, 8 months, and 19 days; the craft would operate for many years past its expected “expiry date.” As of May 15, 2009, the liquid helium coolant on board the SST was exhausted. Without the liquid helium to cool the telescope to the very low temperatures needed for its continued operation, most of the instruments became no longer usable. Aside from the main telescope, the SST carries the following: an Infrared Array Camera (IRAC), which operates simultaneously on four wavelengths; an Infrared Spectrograph (IRS); and a Multiband Imaging Photometer for Spitzer (MIPS), which has three detector arrays in the far infrared. With the depletion of the liquid helium coolant, only IRAC remains operational. SST made valuable contributions to astronomy, with the first images taken showing a glowing stellar nursery, a disc of planet-­ forming debris, and organic material in the distant universe. One of its most noteworthy contributions came in 2005, when the SST became the first telescope to capture light from exoplanets, namely the “hot Jupiters” HD 209458 b and TrES-1b, although it did not resolve that light into actual images. However, this was the firsttime extrasolar planets had actually been seen visually. Before this advance, observations had been indirectly made by drawing conclusions from the behaviors of the stars the planets were orbiting. The term “hot Jupiters” refers to a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods. The close proximity of the planets to the stars around which they orbit result in hot temperatures that have earned them their name. A hot Jupiter orbit would typically be less than one-tenth the distance between Earth and the Sun. Hot Jupiters are found in about 1% of planetary systems. Gas giants with a large radius and very low density are sometimes referred to as “puffy planets” or “hot Saturns,” due to their density being similar to that of Saturn.

190

10.  Astronomical Observatories

Given the nickname Osiris, the exoplanet detected by the SST orbits the star HD 209458 in the constellation of Pegasus, some 159 light years distant. HD209458 is an 8th magnitude star, very similar in nature to our Sun. At magnitude 8, the star cannot be seen with the naked eye, but good binoculars or a small telescope will reveal it. Spectroscopic studies first revealed the presence of a planet around the star on November 5, 1999. The exoplanet HD 209458 b has an orbital radius of seven million km with a surface temperature of 1000 degrees C (1800 degrees F). The exoplanet TrES-1b orbits 02652–01324, an orange dwarf star, in the constellation of Lyra, about 523 light years away. The planet’s mass indicates that it is a Jovian-like planet, similar in bulk composition to that of Jupiter. However, unlike Jupiter, it orbits very close to 02652–01324. TrES-1b was discovered orbiting the star by the Trans-Atlantic Exoplanet Survey, using the transit method, in which the planet was detected crossing its parent star. The Trans-Atlantic Exoplanet Survey, which is no longer operational, was made up of three relatively small Schmidt telescopes, just 4 inches in diameter, located at the Lowell Observatory in Arizona, the Palomar Observatory in California, and a site in the Canary Islands. Armed with CCD cameras that conducted automated sweeps of the sky from these locations, five exoplanets were discovered in total. In 2004, the SST reported the sighting of a faintly glowing body that may be the youngest star ever seen. With Spitzer trained directly on the core of a cloud of gas and dust known as L1014, a dark nebula in constellation of Cygnus, the object appeared in an area that ground-based observatories and the European Space Agency’s (ESA), Infrared Space Observatory (ISO – a predecessor to the SST) had previously been reported as completely dark. After much debate, the conclusion was that the cloud harbored at its core a very young low-mass star, which was named L1014 IRS, with speculation that what SST had witnessed was the earliest stages of star formation. However, some astronomers believe L1014 IRS to be a brown dwarf or even a rogue planet at the earliest stages of formation. Brown dwarfs are objects that are too large to be called planets and too small to be stars. They are thought to form in the same way stars do, from a collapsing cloud of gas and dust. Many brown dwarfs have been found embedded in such clouds. The SST also discovered in April 2005 that Cohen-Kuhi Tau/4, a pre-main-sequence binary T Tauri star system 420 light years distant in the constellation of Taurus, had a planetary disk

Observatories Above Earth

191

that was vastly younger and contained less mass than previously theorized, leading to new understandings of how planets form. Also in 2005, while studying some of earliest images made by the SST, astronomers were led to believe that the telescope may have captured the light of the first stars in the universe! An image of a quasar in the constellation of Draco, intended to help calibrate the SST, was found to contain an infrared glow after the light of the known object was removed, convincing several astronomers working at the Goddard Space Flight Center in Washington, D. C. that the numerous “blobs” in the glow were the light of stars that formed as early as 100 million years ago after the Big Bang, redshifted by cosmic expansion. In April 2015, the SST conducted work alongside the Optical Gravitational Lensing Experiment (OGLE), a Polish astronomical project. The project, which commenced in 1992, is attempting to discover microlensing events. Microlensing is the only known method capable of discovering planets at truly great distances from Earth. An astronomical effect, microlensing was predicted by Einstein’s General Theory of Relativity. As an example, take the light generated from a star. When the light emanating from a star passes very close to another star on its way to an observer on Earth, the gravity of the intermediary star will slightly bend the light rays of the source star, causing the two stars to appear farther apart than they normally would. If the source star is positioned not too close to the intermediary star when seen from Earth, but precisely behind it, this effect is multiplied. Light rays from the source star passes on all sides of the intermediary, or “lensing star,” creating what is known as an “Einstein ring.” Even the most powerful ground-based telescopes cannot resolve the separate images of the source star and the lensing star between them, seeing instead a single giant disk of light, known as the “Einstein disk,” where a star had previously been. The resulting effect is a sudden dramatic increase in the brightness of the lensing star, by as much as 1000 times. This typically lasts for a few weeks or months before the source star moves out of the alignment with the lensing star, and brightness subsides. Together with the Swift Observatory, another NASA spacecraft launched on November 20, 2004, to carry out gamma-­ ray astronomy, Spitzer and the Optical Gravitational Lensing Experiment jointly discovered one of the most distant planets ever identified, a gas giant roughly 13,000 light years from Earth. It was the first time two space telescopes had observed the same micro-

192

10.  Astronomical Observatories

lensing event, all made possible because of the large separation between the two spacecraft, Swift in low-Earth orbit, with Spitzer more than one AU distant in an Earth-trailing heliocentric orbit. This separation provided significantly different perspectives of the brown dwarf, allowing for constraints to be placed on some of the object’s physical characteristics. The SST was the last mission of the NASA Great Observatories program, which saw four specialized telescopes, including the HST, launched between 1990 and 2003. Aside from the SST and HST, there were the Compton Gamma Ray Observatory and the Chandra X-Ray Observatory, each in their own right contributing a great amount of data that could never have been achieved from ground-based observations. However, all of the advantages of such telescopes being placed in space do come at a high price, mainly that of maintenance. Apart from being vastly more expensive to build and place outside Earth’s atmosphere in the first place, should failure occur, the financial impact of repair can be literally astronomical, which is why the era of the space shuttle made such a difference with regard to the HST. Hubble, though, was designed to accommodate regular servicing and equipment upgrades, with five service missions flown by NASA between December 1993 and May 2009. However, long before the HST and its counterparts were launched above Earth’s atmosphere, the Orbiting Astronomical Observatory 2 was to break new ground in space observations, beginning as the forerunner for much greater optical advances in space. Launched on December 7, 1968, an Atlas-Centaur rocket delivered the OAO-2 into a nearly circular 750-km altitude orbit. NASA’s Stargazer achieved LEO and collected data in ultraviolet on many sources including comets, planets, and galaxies. OAO-2 was last heard from in January 1973, but with its two major instruments on board facing in opposite directions, one of its chief discoveries were large halos of hydrogen gas around comets. OAO-2 happened to be in service during the discovery of a nova on February 13, 1970, by Japanese astronomer Minoru Honda (1913–1990). Nova Serpentis 1970, which appeared in the constellation of Serpens in 1970, was important for science because it was one of the first to be observed in multiple wavelength bands including infrared, visible, ultraviolet, and radio. One of the observations made by OAO-2 of the nova that stood out among all the data collected was that the nova became brightest in the infrared 100 days after it was first discovered! Honda, who discovered

Observatories Above Earth

193

twelve comets between 1940 and 1968, was also the first to report the very bright V1500 Cygni (Nova Cygni 1975). The OAO-2 had, on board at one end, the Smithsonian Astrophysical Observatory, also called the Celescope, which, during its length of service, mapped 10% of the sky in several ultraviolet passbands, a range of wavelengths that pass through a filter. In the case of the Smithsonian Astrophysical Observatory, four 12-inch Schwarzschild telescopes that fed into Uvicons, various filters, photocathodes, and electronics aided the collection of data in the passbands. The other end of the OAO-2 housed the Wisconsin Experiment Package (WEP), which in turn had eleven different telescopes for ultraviolet observations. WEP observed over 1200 targets in ultraviolet light before the mission ended in early 1973. During this time, in which a private rivalry was taking place, the importance of space was slowly moving up the agenda of many countries, with the Soviets launching their own space telescope, an ultraviolet telescope named Orion 1, released into the icy darkness from Salyut 1 in 1971. Orion 1 and Orion 2 were a series of two instruments flown to conduct ultraviolet spectroscopy of stars. The Orion 1 space astrophysical observatory was installed in the orbital station Salyut 1, itself a landmark achievement, being the first space station of any kind to be launched into LEO as part of the Salyut program, with five more successful launches of seven more stations to follow. Orion 2 was installed on board Soyuz 13 in December 1973, a spacecraft modified to become the first manned space observatory. The Salyut (“Salute” or “Fireworks”) program spanned a period of 15 years from 1971 to 1986, with the bulk of the missions a success, although two launches failed. The aim of the program was dual purpose, both scientific and military, with four crewed scientific research space stations and two crewed military reconnaissance space stations. The scientific side was an attempt to address the long-term effects of living in space, whether a crew’s general mental and physical state would survive in zero gravity, and in hindsight, the Salyut program was probably very much ahead of its time in the concept, thinking, and strategy. To gain a foothold in space is one enormous step itself, but to have that foothold maintained so that access to a wider platform of exploration can follow was and still is perhaps the true test, given the economic state of the country involved and the literally never-­ending challenge of space.

194

10.  Astronomical Observatories

That said, public attitude towards the ongoing conquest of space also plays a significant role in the overall model of continually pushing back the boundaries of what can be feasibly achieved, and the cost of failure. An enduring American legend holds that the U. S. space program enjoyed broad enthusiastic support during the race to land a man on the Moon. In reality, the only time when more than half of the American public believed Apollo was worth the expense came at the time of the Apollo 11 lunar landing in 1969, when Neil Armstrong took humanity’s first steps on alien soil. Even then, only 53% of the public believed such a momentous historical occasion had been worth the cost. The later Apollo missions were met with general apathy, as it appeared that the very aim of the program had been achieved, placing a man on the Moon. It is therefore vitally important that the pursuit of space in terms of cost and potential human loss is a valid, positive, and ultimately rewarding one. The military aspect of the Salyut program cannot be ignored, and certainly wasn’t at the time. The conducting of space experiments for the good of humankind was tainted somewhat with the use of Salyut as cover for the USSR to fly its highly secretive military Almaz (“Diamond”) stations. The Almaz space station cores were designed as military stations by Soviet mechanics scientist, aviation, and military engineer Vladamir Chelomey’s (1914–1984) OKB-52 organization, designs that were produced long before the Salyut program commenced. Chelomey, who invented the first Soviet pulse jet engine, had a fierce rival in Soviet rocket engineer and spacecraft designer Sergei Korolev (1906–1966), and his OKB-1 organization. Both organizations were involved in the production of missiles and various space and launch vehicles. The pair most notably locked intellectual horns over the Soviet manned lunar program. As early as 1961, the Soviet leadership had made public announcements about landing a man on the Moon and establishing a lunar base. Chelomey had been instructed to develop a Moon flyby program with a projected first flight by the end of 1966. Korolev was tasked to develop the Moon landing program with a first flight by the end of 1967. In 1966, two cosmonaut training groups were formed, one commanded by Soviet test pilot, aerospace engineer, and cosmonaut Vladimir Komarov (1927–1967), who was the first person to fly in space twice, commanding Voskhod 1, the first spaceflight to carry more than one crew member, and

Observatories Above Earth

195

Soyuz 1, of which he was a solo pilot. Tragically, parachute failure caused his Salyut capsule to crash into the ground after reentry on April 24, 1967, making him the first human to die on a spaceflight. His team included Yuri Gagarin (1934–1968), the first human to journey into outer space when his Vostok 1 spacecraft completed one orbit of the Earth on April 12, 1961. The second team was headed up by Air Force Major General and Soviet cosmonaut Alexei Leonov (born 1934), the first person to conduct extravehicular activity (EVA), exiting the capsule during the Voskhod 2 mission, carrying out a spacewalk that lasted for 12 min. Although the Soviets, who had geared themselves up with an extensive program in the design and engineering of a potential manned lunar craft, not to mention the hours spent on training, had every intention of being the first to set foot on the Moon, it wasn’t to be – although the first human-made object to reach the surface of the Moon was Soviet, with Luna 2 touching down on the lunar surface just east of Mare Imbrium near the craters Aristides, Archimedes, and Autolycus. This historic moment on September 13, 1959, was mirrored by America’s Ranger 4 on April 26, 1962, as it too preformed the first hard (unpowered) Moon landing. The hard landing of craft on the Moon, as with any venture into space, is fraught with danger plus an array of many variables that can compromise a mission or ultimately cause its demise. This was very much the case with Luna 1, which due to a ground control system malfunction saw the probe miss its target, the Moon, by 5995 km. That said the mission, although an overall failure, did provide vital information to assist in the understanding of the universe, including observations of the Van Allen radiation belt, noting the existence of a small number of high-energy particles contained within. Also, Luna 1 conducted the first ever measurement of the solar wind. Having missed the Moon, Luna 1 with a twist of irony became the first spacecraft to leave geocentric orbit. The more cynical observer of spaceflight history may suggest an inevitable intertwining of both science and military purposes with regard to the conquest of the stars, even where the Moon is involved. Although Salyut is typical of this, it is hardly alone. However, it does highlight one particular aspect, that for the good of humankind and its overall bettering in the guise of Salyut, the rather darker and politically motivated side of exploration as with Almaz will always exist, as perhaps one cannot exist without the other, given the financial input it commands.

196

10.  Astronomical Observatories

Three crewed military reconnaissance stations were launched under the guise of Salyut from 1973 to 1976, Salyut’s 2, 3, and 5. Salyut 2 was the first Almaz military space station to fly, but it quickly ran into trouble after 2 weeks in operation, the station losing altitude and becoming depressurized after the third stage of the rocket that launched the craft, a Proton, exploded due to pressure changes within the tanks. The explosion created a significant cloud of debris that followed the path of Salyut 2, later striking the craft and most importantly leading to the loss of its two solar panels, rendering Salyut 2 unusable, as it was unable to generate power, leading to orbital decay. The station, which never saw a crew on board, was launched on April 3, 1973. Its orbit steadily declined after the explosion and subsequent issues that developed. Re-entering into Earth’s atmosphere on May 28, 1973, three pieces of the craft were cataloged as surviving a fiery burn-up over the Pacific Ocean. It is important to remember the Salyut program, even if there was controversy about its missions. Salyut broke several spaceflight records, including several mission-duration records, and achieved the first-ever orbital handover of a space station crew to another, an aspect almost taken for granted in modern spaceflight. Salyut also achieved various spacewalk records. COS-B was the first ESA mission to study gamma ray sources. Launched by NASA on behalf of the European Space Research Organization (ESRO) on August 9, 1975, the satellite spent 6.5 years creating a map of the Milky Way and a list of around 25 gamma ray sources. However, with regard to capturing the public’s imagination about just what can be seen when using a telescope above Earth’s atmosphere, the Hubble Space Telescope reigns supreme. Not only because its name honors Sir Edwin Hubble, but it also relays in basic terms exactly what it is doing as space, something that the casual person with just a passing interest in space can easily relate to – a telescope in space. Costing $1.5 billion in 1990, much was pinned on the success of the HST, perhaps a burden that initially seemed too great. Promoted as the observatory that would deliver dazzling and unprecedented views of space that would rewrite human understanding of the cosmos, the anticipation surrounding its debut in LEO was unparalleled. Here, as with Apollo 11 and the first man on the Moon, the wait to see just what the HST could deliver reached fever pitch, as the promise of rich and vibrant views of

Observatories Above Earth

197

nebulas and galaxies, plus all manner of astronomical phenomena, awaited an eager scientific community and a curious public. However, disappointment was to reign down on NASA, as a slip-up during Hubble’s construction phase left its main mirror flawed, with images beamed back during “first-light” reflecting a fuzzy, out of focus universe, a far cry for the promised crisp view of the cosmos. Analysis showed the cause of the problem was that the mirror had been polished to the wrong shape. Despite it probably being the most precisely figured optical mirror ever made, it was deemed too flat, introducing severe spherical aberration, a flaw in which the light reflecting off the edge of the mirror focuses on a different point from the light reflecting off its center. The results were devastating to the images, so much so, an inquest was to follow into just how such a mistake could have occurred. The Allen Commission, headed by Lew Allen, Jr. (1925–2010), then director of the Jet Propulsion Laboratory, set out to determine how such an error could have arisen. The conclusion found failings within NASA itself for quality control shortcomings, but NASA was to blame optical manufacturers Perkin-Elmer for its lack of procedure implementations with regard to supervision of the manufacturer of the mirror, and not assigning its best optical scientists to the task. With an internal inquiry, NASA realized the importance of correcting the situation as quickly as possible, not only to save face but to reassure the public that these sorts of mistakes during the current space era could be put right, something NASA had been more than capable of showing during the Apollo 13 incident. The first Hubble Space Telescope servicing mission, STS-61, launched on December 2, 1993, saw the space shuttle Endeavour restore Hubble’s vision with the installation of a new main camera and a corrective optics package. The mission, and the fifth flight of Endeavour, was the most complex undertaken in the space shuttle era, with its 11-day schedule seeing crew members make five spacewalks (EVAs), an all-time record. Armed with a bank of new instrumentation upgrades and new solar arrays, STS-61 saved Hubble from its three-year plight, catching up with the HST on day two of its mission. Right from the outset, the HST was designed with many different mission parameters in mind, least of all the ability to be regularly serviced, which, given the initial trouble after launch, was a parameter that literally saved the entire project. Five servicing missions were flown by NASA’s space shuttle fleet

198

10.  Astronomical Observatories

(SM1, 2, 3A, 3B, and 4), active between 1993 and May 2009. Servicing missions were delicate operations that began with maneuvering to intercept the telescope in orbit and carefully retrieving the HST with the shuttle’s mechanical arm. Here are the Hubble Space Telescope servicing missions: • STS-61. SM1 – space shuttle Endeavour – December 1993. Installation of several instruments and other equipment over a ten-day period. Most importantly, the installation of COSTAR. • STS-82. SM2 – space shuttle Discovery – February 1997. • STS-103. SM3A – space shuttle Discovery – December 1999. • STS-109. SM3B – space shuttle Columbia – March 2002. • STS–125. SM4 – space shuttle Atlantis – May 2009. The HST was due to have the last service mission in February 2005, but the Columbia disaster in February 2003 meant a grounding of all space shuttle operations until further notice. After one of the most difficult and trying times in not just the history of NASA but in spaceflight in general, the decision was taken to resume operations to the HST for the final time. The work accomplished on the mission rendered the telescope fully operational. On board Hubble, all the instruments are placed in so-called radial instrument bays and axial bays. Four radial bays are placed around the sides of the telescope. Four axial bays behind the mirror at the end of the telescope carry rectangular box-shaped instruments. Various instruments during the duration of Hubble’s mission have occupied both the radial and axial bays. The capability of Hubble is far superior to ground-based telescopes. Ground-based telescopes can seldom provide a resolution better than 0.5–1.0 arc seconds, except for very short times under the very best of observing conditions. Hubble’s resolution is about five to ten times better, or 0.05–0.1 arc seconds. The HST’s mirror-based optical system collects and focuses light that once collected, is then analyzed by the instrumentation on board. The optical system, called the Optical Telescope Assembly (OTA), gives Hubble a unique view of the universe and it gathers, records, and documents data from infrared, visible, and ultraviolet light. It is the modern-day equivalent of artwork on a cave wall, carved images on a tablet of stone, the very quill that conjures the image on a parchment. All are relative, and all attributable to the evolution of humankind’s progressive ability to preserve for others by different means what is being seen.

Observatories Above Earth

199

The OTA is supported by a graphite epoxy skeleton. Found in tennis rackets and golf clubs, graphite epoxy was chosen for the frame of the OTA because it is lightweight, stiff, and strong. Graphite epoxy composite materials are being used increasingly for numerous space applications, with engineers interested in these materials because of their favorable mechanical characteristic of high strength/high stiffness to weight ratio and potential for zero or near-zero coefficient of thermal expansion. Though the skeleton contracts slightly when water vapor embedded within it escapes into space, the graphite epoxy is resistant to expansion and contraction caused by extreme temperature fluctuations experienced as the HST orbits Earth. Temperature fluctuations could also potentially warp Hubble’s mirrors, so the mirrors are kept at a constant 70 degrees Fahrenheit. Hubble used two mirrors, laid out in a Cassegrain telescope design to collect and focus light. They consist of a 2.4-m primary mirror, and a 12-inch secondary mirror. As with the Cassegrain telescope set-up, light travels down the length of the telescope, striking the concave, bowl-shaped, primary mirror. The light reflects off of the primary mirror and travels back toward the front of the telescope. At this point, it hits the secondary mirror, which is convex, or dome-shaped. The secondary mirror concentrates light into a beam the size of a dinner plate that travels back towards and then through a hole in the primary mirror. The light is then directed into the HST’s instrumentation for analysis. One distinct difference from the standard Cassegrain mirrors is how the HST’s mirrors are defined. They are both curved hyperbolically, a much deeper curve than a standard Cassegrain mirror, a variation called the Ritchey-Chretien design (RCT or RC), which provides sharper images over a wider field of view. The same design was present on the Spitzer Space Telescope. The RCT design eliminates off-axis optical errors, the coma. In optics, especially telescopes, the coma or comatic aberration refers to aberration inherent to certain optical designs due to imperfection in the lens or other components. The light is spread out over some region of space rather than focused to a point, causing the image formed by the lens to be blurred or distorted, with the nature of the distortion dependent on the type of aberration. The RCT has a wider field of view free of optical errors compared to a more traditional reflecting telescope configuration. Since the mid-­ twentieth century, a majority of large telescopes have embraced the Ritchey-Chretien design, with the two 10-m Keck telescopes

200

10.  Astronomical Observatories

Fig. 10.3.  Keck observatory, Mauna Kea, Hawaii. (Courtesy of NASA)

at Mauna Kea in Hawaii, and the four 8.2-m telescopes comprising the Very Large Telescope in Chile, plus some of the ground-based observatories using the design. The Ritchey-Chretien telescope was invented in the early 1910s by American astronomer George Willis Ritchey and French astronomer Henri Jacques Chretien (1879–1956). Ritchey worked closely with American solar astronomer George Ellery Hale (1868–1938), best known for his discovery of magnetic fields in sunspots (Fig. 10.3). Ritchey and Hale worked initially at Yerkes Observatory in Wisconsin and then Mt. Wilson Observatory in California, with Ritchey playing a significant role in designing the mirrors at Mt. Wilson. After a disagreement with Hale, and following a trip to Paris where he promoted the construction of large telescopes, he returned to America in 1930 and obtained a contract to build a Ritchey-Chretien telescope for the U. S. Naval Observatory. Indeed, the last telescope he produced remains in service at the naval observatory Flagstaff Station, Arizona. Aside from the creation of the Ritchey-Chretien design, Chretien was also responsible for the creation of the anamorphic widescreen process, using an anamorphic system called Hypergonar, which resulted in the CinemaScope widescreen technique! The size of the primary mirror on the HST allows it to collect 40,000 times more light than the human eye. Though the primary mirror is large, it was designed to be as lightweight as possible.

Observatories Above Earth

201

Instead of a solid core, Hubble’s primary mirror has a honeycomb core, dramatically reducing its weight. Both mirrors are coated with thin layers of aluminum and magnesium fluoride. The aluminum provides the mirror’s reflectivity, and the magnesium fluoride layer provides a coating on top of the aluminum to protect it from oxidation as well as to increase reflectivity of ultraviolet light. Both mirrors and coatings are remarkably smooth, and while Hubble’s primary mirror was ground to the right smoothness, it was not ground to the correct curvature, which led to the error of spherical aberration. The curvature of the mirror was off by less than one millionth of a meter, but was sufficient to leave Hubble with blurred vision. However, even with the flaw, the HST was able to conduct science-based observations not possible from the ground. Installed in 1993, COSTAR (Corrective Optics Space Telescope Axial Replacement) contained small mirrors on robotic arms that corrected the light beams entering Hubble’s original scientific instruments. Orbiting at an average altitude of 569 km, completing one orbit in 97 min at a speed of 28,000 km/h, the HST has delivered some of the most breathtaking views of the universe in which we live. This gigantic eye measuring 13.2 m in length and weighing 11,110 kg, with a maximum diameter of 4.2 m, has opened our eyes to a cosmos that was hitherto shielded by Earth’s atmosphere. Transmitting about 120 gigabytes of science data every week, the HST draws power from our Sun via two 7.62-m solar panels. All of Hubble’s pictures and data are stored on magneto-optical disks, which begs the question, how will future generations store the images of sky that they behold? These are the instruments as of May 2019 currently in use∗ and those replaced: • COSTAR – Corrective Optics Space Telescope Axial Replacement. COSTAR was the instrument designed to correct the initial optical problem suffered by the HST, and in essence is the HST’s ‘glasses,’ the corrective addition that allowed the HST to see again. COSTAR is not really a scientific instrument; it is a corrective optics package that displaced the High-Speed Photometer (HSP) during Servicing Mission 1. COSTAR is designed to optically correct the effects of the primary mirror’s aberration on the Faint Object Camera (FOC). All the other instruments, installed since HST’s initial deployment, were designed with their own corrective optics.

202

10.  Astronomical Observatories

• COS – Cosmic Origins Spectrograph.∗ COS breaks down ultraviolet radiation into components that can then be studied in finer detail. It is used to examine galaxy evolution, the formation of the planets, the rise of the elements needed for life, and the “cosmic web” of gas that exists between galaxies. The instrument was designed to perform high-sensitivity medium and low-resolution spectroscopy of astronomical objects, and its installation significantly enhanced the spectroscopic capabilities of HST at ultraviolet wavelengths, providing astronomers with unparalleled opportunities for observing faint sources of ultraviolet light. The instrument was installed on HST during Servicing Mission 4 in May 2009. • ACS – Advanced Camera for Surveys.∗ ACS conducts surveys of the universe and studies the nature and distribution of galaxies. It studies ultraviolet emissions from stars, takes pictures of other planets in our Solar System, and is used to search neighboring stars for the possible existence of other planets. The ACS is classed as a third-generation HST instrument, installed during Servicing Mission 3B. During Servicing Mission 4, the ACS was repaired after an electronic malfunction in 2007. • STIS – Space Telescope Imaging Spectrograph.∗ The STIS is a very versatile instrument. It acts somewhat like a prism, separating light from the cosmos into its component colors. The instrument is used to study black holes, the composition of galaxies, and the atmospheres of planets orbiting other stars. The STIS provides spatially resolved spectroscopy in the UV and optical, high spatial resolution echelle spectroscopy in the UV, and solar-blind imaging in the optical. The STIS was installed aboard HST during Servicing Mission 2 in 1997 and operated until an electronic failure in 2004. It resumed operations with all ultraviolet and optical channels in 2009 after it was successfully repaired during Servicing Mission 4. • NICMOS – Near Infrared Camera and Multi-Object Spectrometer.∗ NICMOS is Hubble’s heat sensor. Its sensitivity to infrared light makes it useful for observing objects obscured by interstellar gas and dust (such as stellar birth sites and planetary atmospheres) and is also used for peering into the deepest regions of space possible. NICMOS has three adjacent but not contiguous cameras designed to operate independently, each with a dedicated array at a different magnification scale. • FGS – Fine Guidance Sensors.∗ The FGS are basically not unlike finder scopes, locking on to “guide stars,” measuring their posi-

Observatories Above Earth









203

tions relative to the object that is being viewed. Together with the configuration established, adjustments based on these precise readings allow Hubble to maintain a position of literally being pointed in the right direction. The sensors also perform the task of conducting celestial measurements. The FGS, in addition to being an integral part of the HST Pointing Control System (PCS), provide astronomers with the capability of precision astrometry and milli-arcsecond resolution over a wide range of magnitudes. FOC – Faint Object Camera. The FOC was one of the four original axial instruments aboard the HST and was designed to take imaging observations of astrophysical sources from the near ultraviolet to the near infrared. The instrument was removed from the HST during Service Mission 3B in March 2002. WFPC1 – Wide Field and Planetary Camera 1. The WFPC1 was used from April 1990–November 1993 to obtain high resolution of images of astronomical objects over a relatively wide field of view and a broad range of wavelengths. WFPC1 was replaced by WFPC2 during the first servicing mission to HST in 1993. WFPC2 – Wide Field and Planetary Camera 3. For many years, the WFPC2 was the HST’s workhorse camera. Before being replaced by WFC3 during Servicing Mission 4 in 2009, it recorded images through a selection of 48 color filters covering a spectral range from far-ultraviolet to visible and near-infrared wavelengths. The “heart” of the WFPC2 consisted of an L-shaped trio of wide-field sensors and a smaller, high-resolution (planetary) camera placed at the square’s remaining corner. The astronomical phenomenon captured by the WFPC2 in stunning resolution and excellent quality were released as public outreach images over the years, making the WFPC2 the most used instrument in the first 14 years of Hubble’s life. Indeed, the WFPC2, about the size of a baby grand piano, has been dubbed Hubble’s “savior” camera and after a return flight courtesy of the space shuttle, resides as a display piece at the Smithsonian National Air and Space Museum in Washington, D. C., alongside parts from its predecessor, WFPC1. WFC3 – Wide Field Camera.∗ The WFC3 can be used to study objects everywhere from the far-distant universe to our very own Solar System. It helps examine the way galaxies evolve over time, studying the history of individual galaxy evolution and the mystery of dark energy, the force that appears to be accelerating the expansion of the universe. The WFC3 is a

204

10.  Astronomical Observatories

fourth-generation UVIS/IR imager, installed in May 2009 during Servicing Mission 4, replacing the WFPC2. • FOS – Faint Object Spectrograph. The FOS was one of the four original axial instruments aboard the HST. It was designed to make spectroscopic observations of astrophysical sources from the near-ultraviolet to the near-infrared. The instrument was removed from the HST during Servicing Mission 2 in February 1997. • GHRS – Goddard High Resolution Spectrograph. The GHRS was one of the four original axial instruments on board the HST. It was designed to take spectral observations of astrophysical sources. The instrument was removed from the HST during Servicing Mission 2 in February 1997. • HSP – High Speed Photometer. The HSP was one of the four original axial instruments onboard the HST. It was designed to make very rapid photometric observations of astrophysical sources in a variety of filters and passbands from the near ultraviolet to the visible. The HSP was removed from HST during the first servicing mission in December 1993. Despite its age and only modest size compared to the vast 8–10-m telescopes built for ground-based observations, Hubble has constantly outperformed many of them, and at its zenith must be considered to be at the pinnacle of optical and ultraviolet astronomy until a replacement is installed. Racking up an impressive 1.3 million observations since first light in 1990, Hubble has peered back into the very distant past, to locations more than 13.4 billion light years from Earth. Hubble has helped astronomers estimate the age of the universe, 13.8 billion years old, roughly three times the age of Earth, and has been instrumental in determining the rate at which the universe is expanding. Hubble has discovered that nearly every major galaxy is anchored by a black hole at its center. Hubble discovered two new moons orbiting Pluto, Nix, and Hydra. The moons were measured at a distance of approximately 44,000 km away from Pluto, 2–3 times as far from Pluto as Charon, the previously known moon. Measuring approximately 64–200 km in diameter, these tiny moons are dwarfed by Charon, which measures 1170 km wide, with Pluto itself measuring 2270 km in diameter. Both tiny moons are 5000 times fainter than Pluto. Hubble’s presence in orbit has been almost sentry-like, a lookout post even, ready to focus in on any astronomical event, such as, in 1994, the rare cometary impact, taking images of a

Observatories Above Earth

205

huge plume of debris created as Comet Shoemaker-Levy 9 plowed into Jupiter. In 1995, Hubble took one of its most famous photographs, that of the Eagle Nebula, later named the “Pillars of Creation.” HST also assisted in the production of a 3-D map showing the distribution of dark matter in the universe. Astronomers also received their first image of an exoplanet when in 2008 Hubble photographed Fomalhaut b. Active from 2009 to 2013 was ESA’s Herschel Space Observatory, the largest infrared telescope ever launched. As with NASA’s Great Observatories program, Herschel was the fourth to be launched of four significant missions, named Cornerstone, part of ESA’s Horizon 2000 program. Herschel followed SOHO/ Cluster II, the Solar and Heliospheric Observatory, XXM-Newton, an X-Ray Space Observatory, and Rosetta. The Rosetta spacecraft, along with Philae, its lander module, performed a detailed study of comet Churyumov-Gerasimenko. Launched from French Guiana, the Herschel Space Observatory sifted through star-forming clouds to trace the path by which potentially life-forming molecules, such as water, form. Its mission parameters included investigating galaxy formation in the early universe and the evolution of galaxies. The observatory made over 35,000 scientific observations with more than 25,000 h’ worth of data from 600 different observing programs. The observatory was instrumental in the discovery of an unknown step in the star forming process. Launched by Arianespace from French Guiana on December 19, 2013, the Gaia space observatory is designed for astrometry – the measuring of positions, distances, and motions of the stars with unprecedented accuracy. The mission aims to construct by far the largest and most precise 3D space catalog ever made, totaling approximately one billion astronomical objects including planets, asteroids, comets, and stars. Gaia is part of ESA’s Horizon 2000+ long-term scientific program along with the LISA Pathfinder, a mission that tested technologies needed for the Laser Interferometer Space Antenna (LISA) and BepiColombo, a joint ESA and Japan Aerospace Exploration Agency (JAXA) reconnaissance mission to Mercury, using two unique spacecraft. In 1989, the ESA satellite Hipparcos (High Precision Parallax Collecting Satellite), led the way with the first space experiment solely devoted to precision astrometry. The resulting Hipparcos Catalogue, a high-precision compendium of more than 118,200 stars, was published in 2007. The lower-precision Tycho

206

10.  Astronomical Observatories

Catalogue, of more than a million stars, was published at the same time, while the enhanced Tycho-2 Catalogue of 2.5 million stars was published in 2000. Both Tycho catalogs were based on observations made using Hipparcos. The information obtained by Gaia’s astrometric measurements will in turn yield information on the kinematics (motions of bodies and systems of bodies, the geometry of motion), and subsequently an insight into the physical origin of the Solar System and our own Milky Way. Among a great array of tasks during its mission, Gaia will provide spectrophotometric measurements detailing physical properties of all the stars observed, characterizing their luminosity, effective temperature, gravity, and elemental composition.

The Future of Space Travel Despite all the space observatories launched, there are more in the planning stages and on the drawing board. There can be no doubt about the advantages of a having a telescope in space, with each new addition performing greater, more intricate tasks, while continuing to look deeper into space with a more significant number of finely tuned instruments on board. Space observatories will always be required, but in a larger, more complex picture, they form just a part of the overall vision that must be honored in space if humankind is to continue to not only push back the scientific boundaries but also the physical boundaries that limit them in the form of manned spaceflight. The two are inseparably intertwined, and one cannot properly function if the other is not prepared to advance alongside it. NASA, ESA, the Indian Space Research Organization (ISRO), the Soviet space program, later succeeded by Roskosmos, along with both the China National Space Administration and the Japanese Space Agency, will all strive to place their technology at the forefront of what is becoming a very crowded segment of space around Earth. Several factors will determine each individual project, with the Moon having returned to favor from some countries as a target for potential development, although not always with science top of the list of reasons why. Mars, too, drifts in and out of focus as the next logical step in the progression away from Earth, but the undertaking is enormous, let alone hazardous and extremely

Gamma Ray, X-ray, and Infrared – Multi-­Messenger Astronomy

207

expensive. However, with a budget in place and properly trained crew, it is an achievable goal. The need for humankind to move beyond where we are now is not only essential but vital to the progression of our development of space, and while placing hardware in LEO has become routine, with a sideways shift evident in making the Moon once again become a conquest that in many ways has already been achieved, Mars must surely stand out as the next logical step to try and embrace humankind’s glorious exhale from Earth outwards. To stagnate would be a travesty to all those who gave their lives making it this far, and to the vast amount of people who live and work for the advancement of our understanding of space itself through manned missions, the biggest of which would be a Martian rendezvous. Many souls have been lost as the boundaries and barriers have been pushed back and overcome – from the tragic loss of Vladimir Komarov in 1967, one of the first group of cosmonauts selected to attempt space travel, and the very first fatality in space, to the three cosmonauts who manned Soyuz 11, the only manned mission to board the world’s first space station, Salyut 1. Their mission ended in disaster when the crew capsule depressurized during preparations for re-entry. The three crew members of Soyuz 11 are the only humans known to have died in space. To the seven astronauts lost on STS-51-L, the Challenger space shuttle disaster on January 28, 1986, and the space shuttle Columbia disaster of February 1 2003, where seven more lost their lives. Also, to those who strived to firstly put the likes of Apollo 13 into space, and then ultimately bring home the crew when the odds of achieving this seemed very much against them seeing home again.

 amma Ray, X-ray, G and Infrared – Multi-­Messenger Astronomy Besides optical and radio, advances over the years have meant astronomy has entered a brand-new arena of observation, that of studying the universe through a different set of “eyes,” eyes that would allow humankind to view phenomena on a contrasting level, one that would unlock various secrets that up until now have been hidden. The possibilities of using this new technology would not just be restricted to delving into areas of space yet to

208

10.  Astronomical Observatories

be investigated, but would give astronomers the chance to study every inch of the sky that had already been observed, adding a sort of layer effect on top of optical and radio. Here, a new chapter in the recording of astronomical phenomena, far removed from cave art and ancient texts but a continuation of the thread that has woven its way through the fabric of humankind, touching all who have used various means of recording the night sky. Here, just as the likes of bright stars and phases of the Moon were recorded on parchment, they are being observed again centuries later with new techniques, meaning that the thread has connected those who saw the same object, like the Sun, but gazed at it in different times. As was the case in the past, today’s observations will be just another steppingstone to a new and alternative way to see the Sun again in the future, as the thread continues its weaving passage through both space and time. It has long been known that X-rays emitted from astronomical objects are absorbed by Earth’s atmosphere, so any instruments required to detect such X-rays must be positioned at high altitude or, preferably, in space itself. Emissions are expected from astronomical objects that contain extremely hot gases. The existence of solar X-rays was confirmed at the very early stages of rocket flight. The first cosmic X-rays were discovered by a sounding rocket in 1962. These sounding rockets were actually rockets captured by the U. S. Army at the end of World War II. From the White Sands Missile Range in southern New Mexico, these rockets were converted to carry scientific instruments into Earth’s upper atmosphere. Named Scorpius X-1, this was the first extrasolar X-ray source discovered, although the possible existence of such phenomena was first proposed by Italian experimental physicist Bruno Benedetto Rossi (1905–1993), who, at the time, set about encouraging the necessary officialdom to sponsor searching in space for possible emissions. As a result of his efforts, a team led by Professor Riccardo Giacconi (1931–2018) and an Aerobee 150 rocket was launched on June 12, 1962, carrying a highly sensitive soft X-ray detector that had been designed by scientist Frank Paolini. Despite veering slightly off course (the intended study source being the Moon prior to the launch of astronauts), Scorpius X-1 was detected 9000 light years away in the constellation of Scorpius. Had there been no unintended course deviation, it might not have been found! The discovery led to further rocket flights, making it clear over the coming years that Earth is being showered by X-rays

Gamma Ray, X-ray, and Infrared – Multi-­Messenger Astronomy

209

from virtually everywhere. So bountiful were the signals that they exceeded the Sun’s entire energy output by a factor of 100 and exceeded the Sun’s X-ray output by a factor of about 100 million! Naturally, after finding the source in Scorpius, the hunt began to find the “star” associated with emitting the X-ray light. The answer came in the form of a blue object in the constellation of Scorpius, V818 Scorpii, which continues to emit X-rays even today. The flux of V818 Scorpii varies from day to day. It is a neutron star paired with a low mass star, its magnitude ranging from +11.9 to +12.8. In the 1970s, the field of X-ray astronomy grew with a series of satellites that were built on the work of the 1962 discovery, the first of which was named Uhuru. Uhuru was the proposal of Giacconi and fellow scientist Herb Gursky (1930–2006), with the pair arguing the craft were required to enter space in order to make longer duration studies of X-ray sources. Giacconi and Gursky (Gursky being the man who actually launched the Aerobee 150 rocket on June 12, 1962), both experts in the field, intended for Uhuru to survey the sky for cosmic X-ray sources and determine precisely their source and location. Uhuru, or the X-ray Explorer Satellite, SAS-A (“Small Astronomy Satellite”), was launched on December 12, 1970, the first satellite with the specific purpose of performing X-ray astronomy. Uhuru spent several years scanning the heavens until its mission ended in March 1973, and among the results were the discovery of binary X-ray sources such as Cen X-3, Vela X-1, and Her X-1, and the first strong candidate for an astrophysical black hole, Cygnus X-1. In time, Cygnus X-1 became recognized as the first such source to be generally accepted as a black hole, remaining one of the most studied astronomical objects in its class. All told, Uhuru discovered 300 new X-ray sources. Cygnus X-1 is one of the strongest X-ray sources we can detect from Earth, and it is believed that the black hole was not produced by a supernova but may have been the result of a massive star that collapsed without an explosion. Although the discovery was a major step in the field of X-ray astronomy, the next course of action was to determine exactly where the source was; it seemed positioned somewhere deep in the heart of the constellation of Cygnus, the Swan. The source appeared to be very close to a star named HDE 226868. However, that wasn’t the radio source of the X-ray and radio emissions because it wasn’t hot enough to generate such

210

10.  Astronomical Observatories

strong radiation. Further observations revealed something large enough to be a black hole, orbiting a system with a blue supergiant star. The system itself could be at least five billion years old, which is about the right age for a 40-solar-mass star to live, lose a portion of its mass, and then collapse to form a black hole. The radiation is likely coming from a pair of jets that extend out from the black hole – which would be capable enough to produce such strong X-ray and radio signals. The 1970s also saw the launch of Ariel 5, the Small Astronomy Satellite (SAS-3), the Orbiting Solar Observatory (OSO), and the High Energy Astronomy Observatory (HEAO-1), all contributing to the research of X-rays and all instrumental in developing the field at an astounding pace. Ariel 5 was a joint British and American space telescope launched on October 15, 1974, from the San Marco platform in the Indian Ocean. Ariel 5 carried six experimental payloads, including research in X-rays and photons. The craft, though, was noted in its mission, which ended on March 14, 1980, for the discovery of V616 Monocerotis, the nearest known black hole to Planet Earth. Also known as V616 Mon, the black hole is located about 3000 light years away and has between 9–13 times the mass of the Sun. Cygnus X-1 is the next closest black hole at a distance of 6070 light years away. The 1980s and following decades saw more advanced and sophisticated satellites launched, including the European X-ray Observatory (EXOSAT), ASTRO-C, renamed Ginga (Japanese for ‘galaxy’), the Rossie X-ray Timing Explorer (RXTE), Rontgensatellit (ROSAT) – in German, X-rays are called Rontgenstrahlen in honor of Wilhelm Rontgen (1845–1923) – the Advanced Satellite for Cosmology and Astrophysics (ASCA), and the Italian-Dutch satellite for X-ray astronomy named BeppoSAX, with ‘Beppo’ derived from Italian physicist Guiseppe Paolo Stanislao “Beppo” Occhialini (1907–1993) and ‘SAX’ standing for “Satellite per Astronomia a raggi X,” or “Satellite for X-ray Astronomy.” This decade also saw the launch of the US-UK-Netherlands Infrared Astronomical Satellite (IRAS), on January 25, 1983. IRAS, the first space observatory to map the entire sky in infrared wavelengths detected, went into polar orbit at an altitude of 900 km, being blasted into space from the Vandenberg Air Force Base in California courtesy of a Delta rocket. In 2003, 20 years later, (SST), formerly the Space Infrared Telescope Facility (SIRTF). At a cost of $720 million, Spitzer,

Gamma Ray, X-ray, and Infrared – Multi-­Messenger Astronomy

211

named after American theoretical physicist Lyman Strong Spitzer, Jr., the craft outlived its expected duration in space, retiring in January 2020, with notable results including the finding that our very own Milky Way has a more substantial bar structure across its core than previously thought. These bars affect both motions of stars and interstellar gases within the galaxy. While collating and examining the vast amount of data sent back by the SST, some 400 h of observations, astronomers also discovered that Spitzer, on one of its earliest images, had captured the light of the first stars in the universe. The 1990s saw the launch of the Compton Gamma Ray Observatory (CGRO), which spent time in orbit from 1991 to 2000. The CGRO was recognized for its advancement in the study of gamma rays, but it wasn’t the first telescope of its nature to be launched. That credit belongs to Explorer 11, an ingenious telescope in a satellite that was to provide the first view of the universe at the shortest wavelength of the electromagnetic spectrum. The Explorer 11 (S15) was the first Earth-orbital satellite to carry a space-borne gamma-ray telescope. Launched on April 27, 1961, by a Juno II rocket, Explorer 11’s mission returned dramatic results, detecting 22 gamma-ray events and 22,000 from cosmic radiation, radiation that mainly originates from outside our Solar System from distant galaxies. During a period of 4 months after becoming correctly positioned in orbit around Earth, Explorer 11 provided nearly 20 miles of data on microfilm. Reconstruction of the data allowed gamma-ray times of arrival to be determined to 0.1 s, and where the gamma-ray detector (measuring just 20 inches high, 10 inches in diameter, and weighing just 30 pounds) was pointed to about 5 degrees. The CGRO, launched in 1991, mapped thousands of celestial gamma-ray sources, with mysterious bursts situated throughout the sky, implying that their sources are at the distant reaches of the universe, rather than in the Milky Way. One of NASA’s “Great Observatories,” the CGRO, named in honor of American physicist Arthur Holly Compton (1892–1962), operated until 1999. Compton was the scientist behind the “Compton effect” caused by the transfer of energy from a photon to an electron, confirming the dual nature of electromagnetic radiation as both a wave and particle. Deployed by the space shuttle Atlantis (STS-37) on April 11, 1991, the 16-ton satellite CGRO was the heaviest payload ever flown at the time, at a cost of $617 million. Its findings included

212

10.  Astronomical Observatories

one of the brightest gamma-ray bursts (GRB) recorded at the time, 990,123, which was the first GRB for a which a simultaneous optical flash was detected. The burst was picked up by the CGRO on January 23, 1999, with the Robotic Optical Transient Search Experiment (ROTSE-I) telescope in Los Alamos, New Mexico, sighting the visible-light image on the same day as it occurred. ROTSE-I (of which there were sequel versions) was able to respond as it was directly receiving signals from an instrument on the CGRO, literally responding in seconds, without any human intervention. CGRO paved the way for further missions such as the ESA International Gamma-Ray Astrophysics Laboratory (INTERGRAL), launched on October 17, 2002; NASA’s Swift Gamma-Ray Burst Mission, later renamed the Neil Gehrels Swift Observatory launched on November 20, 2004 (after American astrophysicist Cornelis A. “Neil” Gehrels, 1952–2017); and NASA’s Fermi Gamma-ray Space Telescope (FGST), formerly called the Gamma-­ ray Large Area Space Telescope (GLAST), launched on June 11, 2008. Also launched in the 2000s was the LISA Pathfinder, formerly known as the Small Missions for Advanced Research in Technology-2 (SMART-2). LISA’s mission was to pave the way for future missions by testing in flight the very concept of gravitational wave detection. This decade also saw the launch on June 30, 2001, of the Wilkinson Microwave Anistropy Probe (WMAP), previously known as the Microwave Anisotropy Probe (MAP). WMAP produced an image of the early universe that contained intricate detail, making for one of the most important scientific results in recent years prior to the WMAP’s launch. Following WMAP was the Planck Space Observatory, which set out to map the anisotropies of the cosmic microwave background (CMB). The ESA mission, which launched on May 14, 2009, produced an all-sky map of the cosmic microwave background, suggesting that the universe is slightly older than thought. According to the map, subtle fluctuations in temperature were imprinted on the deep sky when the universe was about 370,000 years old, the imprint reflecting ripples that arose as early in the existence of the universe as the first nonillionth of a second! Search results carried out by both X-ray, gamma-ray, infrared, and microwave satellites and observatories continue to be analyzed today, with the data collected not only taking years to actually

Gamma Ray, X-ray, and Infrared – Multi-­Messenger Astronomy

213

study, but as a useful source reference that can be examined against any newly obtained findings. One such case relates to the Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), which was launched on July 23, 1999. Named after Indian-American astrophysicist Subrahmanyan Chandrasekhar, CXO provided astronomers with the first light image of supernova remnant Cassiopeia A, as well as recording the first X-ray emission from the supermassive black hole, Sagittarius A∗, at the center of the Milky Way. The latter finding led to an even greater discovery while researchers were scrutinizing the massive amount of data sent back by the CXO. In April 2018, news broke of research that suggested that as many as dozen black holes may lie at the center of the Milky Way, supporting a widely held theory that “supermassive” black holes at the centers of galaxies are surrounded by many smaller ones. A Columbia University-led team of astrophysicists made the discovery of the black holes, which are gathered around Sagittarius A∗ (Sgr A∗). As a part of extensive research, it was discovered that Sgr A∗ was surrounded by a halo of gas and dust that provides a perfect breeding ground for the birth of massive stars, which live, die, and could eventually turn into black holes. As an addition to the black holes that may well form naturally following the death of a star, outside of the halo, smaller black holes are believed to fall under the influence of supermassive black holes (SMBHs), and as the smaller holes lose energy, they subsequently get drawn in, eventually being held captive by the SMBHs. Although a suspected majority of black holes that fall under the influence of a SMBH remain isolated, some capture and bind to a passing star, forming a stellar binary. In a search of finding X-rays emitted from these binary systems, the team, led by astrophysicist Chuck Hailey, sifted through archival data collected from the Chandra X-ray Observatory, hunting down possible X-ray signatures of black hole-low mass binaries in their inactive state, discovering 12 within 3 light years of Sgr A∗. Black holes in an isolated state emit little or no detectable X-rays, but in a mated state as a stellar binary, X-ray bursts are detectable – weak, but consistent and steady. Further investigation that analyzed the properties and spatial distribution of the identified binary systems, concluded that there could well be anywhere from 3000 to 5000 black hole-low mass binaries and about 10,000 isolated black holes in the area surrounding Sgr A∗.

214

10.  Astronomical Observatories

Much is still to be learned about black holes, but the work of such greats as English theoretical physicist Professor Stephen Hawking (1942–2018) has meant that astronomers have a significantly better insight into the workings of these strange yet intriguing phenomena. Just a few years before his death, Hawking stated that not all information is lost when something enters a black hole, and there might be a possibility to retrieve information from it. There lies an interesting prospect for future missions and an intriguing legacy as to what colleagues can develop over the years to come as we continue to push back the boundaries of our knowledge about black holes.

11.  Fossils, Tree Rings, and Ice Mother Nature’s Records Our documenting of the night sky throughout history is not bound to wording and artwork, as many other forms of historical records exist and potentially more ways to record may come to light as we re-visit and re-examine certain structures and archaeological finds whose true definition and original meaning may have been misinterpreted. Nature has many ways of preserving the past and, in so doing, helps us recall events of the past. Undisturbed and allowed to naturally record events in a manner unrecognized in years past, the planet reveals a history that probably relates a more accurate record of any past events than could ever have been imagined  – unchanged, unaltered, untarnished, and in the most natural form possible. The more we learn from what nature is trying to tell us, the better we may understand, as current custodians, how to not upset the equilibrium, and to ensure that information continue to be recorded in the form that has lasted centuries.

Fossils Fossils can yield a whole spectrum of information, information that can relate to the living habits of creatures long since extinct. We can gather data on their environment and the surroundings in which they lived, how old they were when they died, and in some cases, how they died. However, some fossils reach far beyond that capacity, imparting knowledge of events light years away, such as a supernova. Supernova ash has been discovered in fossils that were created by bacteria on Earth. Because the fossils contain a variety of iron that is most likely the product of a supernova event that occurred light years from Earth, the finding also suggests that the event might have played a role in an extinction event on Earth. Research has shown that supernovas generate a mildly radioactive © Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4_11

215

216

11.  Fossils, Tree Rings, and Ice

variety of iron known as iron-60. The outburst from a supernova hurls vast amounts of iron-60 – more than 5–10 times the mass of the Sun – out into space. Iron-60 that is produced in other natural ways creates only up to one-tenth as much. As such, iron-60 that is found on Earth and on our Moon is likely to be ash that has come from supernovas. Scientists have for many years suggested that a supernova at least 325 light-years from Earth blasted the planet with iron ash about two million years ago, and in an attempt to look for traces of the debris that could be associated with the supernova, have analyzed core samples of marine sediment, extracted from the Pacific Ocean, dating back to the respective timeline. Iron-60 was discovered within fossilized chains of magnetic crystals of a mineral known as magnetite. These so-called “magnetofossils,” measuring just billionths of a meter in size, were created by microbes known as magnetotactic bacteria, with scientists drawing the parallel that the core samples in which the iron-60 appear date back to around 2.6  million and 2.8  million years ago. Supernova debris apparently rained down on Earth for about 800,000 years, with iron-60 levels peaking about 2.2 million years ago. The connection would also coincide with the extinction event that claimed mollusks such as marine snails and bivalves, with a period of global cooling occurring during that time as well. The search for fossils and the clues they conceal within isn’t confined to Planet Earth. If Earth’s fossils can relate to us past life on our own planet, the finding of fossils on another world would provide conclusive evidence that life did exist, or in the extreme still does, on the likes of Mars, a planet that has provoked much speculation about its past. The discovery of fossils would be the only way to once and for all put a long-standing debate to rest. We know that most fossils studied on Earth are found in sedimentary rock, which is laid down in layers that slowly hardens into true rock. But most of Mars is made up of volcanic rock, more like the material that lines the bottom of Earth’s ocean floors. Though this rock also contains fossils, they are significantly harder to find. In an environment on Mars that perhaps billions of years ago was more hospitable, wetter perhaps, with plant life, the search for the clues to its past will seemingly only be found in the volcanic rock. This type of rock manifests itself with many fissures, cracks, and crevices, and microorganisms are adept at working their way into those cracks. When they eventually die, they remain inside the volcanic rock, where they can be preserved for millions of years,

Fossils

217

and it is here the best chance exists of determining if there really was life on Mars. Debate still surrounds the alleged microscopic fossils that were found within a meteorite in Allan Hills, Antarctica, on December 27, 1984, by a team of U. S. meteorite hunters from the Antarctic Search for Meteorites (ANSMET) project. Funded by the Office of Polar Programs of the National Science Foundation (NSF), scientists look for meteorite falls in the Transarctic Mountains, which are comprised of a range of uplifted sedimentary rock in Antarctica. The meteorite, which was thought to have been blasted off the surface of Mars by a meteor impact about 17  million years ago, was discovered while the team of geologists was venturing through the Allan Hills on snowmobiles. The meteorite, named Allan Hills 84001 (ALH 84001), originally formed four billion years ago on Mars and landed on Earth about 13,000 years ago. The more skeptical view is that it is not Martian bacteria, as one by one, every line of evidence for life has been given a non-­biological explanation. However, ALH 84001 is not alone. Another discovery, ALH 77005, has displayed another tantalizing clue, the presence of a mineralized and filament-like organic material embedded inside the rock. ALH 77005 was discovered in 1977 by the Japanese National Institute of Polar Research mission (1977–1978). The meteorite, estimated to be 175 million years old, is similar to the Shergotty meteorite, which fell at Sherghati, India (formerly spelled Shergotty), in 1865. About three-quarters of all known Martian meteorites are Shergottites. Like other Martian meteorites, ALH 77705 is known to have originated on Mars because it has a composition similar to rocks and atmosphere gases analyzed by Mars spacecraft. The Curiosity rover, launched by NASA from Cape Canaveral on November 26, 2011, confirmed the connection between Mars itself and these meteorites, having analyzed the presence of argon in the Martian atmosphere, which was found to be the same as argon traces in meteorites. Closer to home, there is an abundance of places on our very own Moon that could harbor important insight to early life on Earth. Just as Mars was subject to meteorite impact from which its own debris sprang forth, the same applies to Earth. Meteorites found on Earth that were created by impacts on the Moon and Mars suggest that cosmic bodies regularly have rocks propelled at each other.

218

11.  Fossils, Tree Rings, and Ice

Fig. 11.1.  ALH 84001. (Courtesy of NASA.)

That said, after all the missions to the Moon, not one single rock from the hundreds of lunar samples recovered was an Earth meteorite on the Moon (Fig.  11.1). In essence, what scientists would be looking for is the equivalent of ALH 84001, a Mars to Earth scenario, whereby a chunk of rock that contained microscopic fossils was ejected from Earth, landing up on the Moon!

Tree Rings Dendrochronology is the scientific study of dating tree rings to the exact year they were formed. Tree-ring dating also supplies valuable data to dendroclimatology, the study of climate and atmospheric conditions during different periods in history, gathered solely from the examination of the rings. The data collected from the study of tree rings is of great use to many people from many walks of life, including the archaeologist, for the purpose of dating materials and artifacts made from wood. Indeed, when used in conjunction with other methods, tree rings can be used to plot events.

Tree Rings

219

Aside from the use in dendrology, which allows the dendrologists, tree scientists, to determine local climate conditions, with the added application in the field of forestry management and conservation, chemists also find use from the tree rings, a method by which radiocarbon dates are calibrated. However, it’s the insight given to the field of paleoclimatology that finds its link to astronomy, where environmental conditions of the past, locally or globally, are displayed in the ring structure, and with the gained insight, perhaps the wood also offering a lesson about climate change in the future. Could the rings, therefore, show great climatic shifts and offer a reason for any shifts, perhaps from an outside influence, like the impact from some cosmic debris? Trees evolved around 380  million years ago, with the tree ancestors taking on the appearance of what we see today, but not in any properly formed sense. The dawn of the age of trees as we know them came with the evolution of wood in the late Devonian Period. The Devonian – so named as rocks from the period were first studied in Devon, England  – is a geological period of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2  million years ago, to the beginning of the Carboniferous, 358.9  million years ago. The Devonian Age, often dubbed the “Age of Fish” because of the substantial diversity of fish at the time, saw the first significant adaptive radiation of life on dry land, with free-sporing vascular plants beginning to spread across land, forming extensive forests that covered the continents. Trees as we recognize them today replaced the giant fern-type look of their predecessors, developing a woody, strong stem that would hold the tree steadfast in the years to come as it grew and flourished. Branches would form as the tree embraced the sunlight for photosynthesis reproduction. Each season of growth, a new ring is set down in the body of the tree, clearly visible in any stump, with a series of concentric rings circling the heart of the wood and fanning out towards the edge, the outer rings representing the youngest years of the tree. However, the rings aren’t uniform; some are thicker, some thinner, with a variance in how dark or how light they are. The differences represent conditions of the season or the year, and determining what influences caused what type of ring is at the center of dendrochronology.

220

11.  Fossils, Tree Rings, and Ice

To establish an overall pattern with regard to an event or climate shift, a single record of rings from a single tree is insufficient. In order to produce a credible sample and reflection of a certain time period, it is necessary to combine the records of literally hundreds or indeed thousands of tree rings, and only then can a pattern be established. It took the insightfulness of astronomer Andrew Ellicott Douglass (1867–1962) to pioneer the potential correlation between tree rings and the sunspot cycle, founding the discipline of dendrochronology. Douglass, born in Windsor, Vermont, started his discoveries in the field while working at the Lowell Observatory in Flagstaff, Arizona, working alongside mathematician and astronomer Percival Lowell, who formed the beginning of the effort that led to the discovery of Pluto fourteen years after his death, in 1930. However, a difference of opinion with regard to the existence of artificial canals on Mars, and visible cusps on Venus, meant the two were to fall out. Douglass cast doubt over Lowell’s controversial and ultimately incorrect opinion, causing Douglass and Lowell to eventually part ways. Douglass’ interest lay in solar flares, and it was his belief that sunspots were linked to changes in Earth’s climate. Armed only with sunspot records dating back to the 1600s, there was no way that Douglass could prove his theory without recorded weather patterns, which, when correlated with sunspot activity, might show the link that he firmly believed. After much research, Douglass believed that the answer could lie within tree rings. The theory never properly panned out for Douglass, but it did open up a new scientific gateway for further investigation with dendrochronology assisting many a discipline in the years that followed.

Solar Storms Douglass’ trail, that had seemingly gone cold, was to be reignited later. A team of researchers picked up Douglass’ baton, suggesting that tree rings were responsible for revealing an unexpected solar event that occurred 7000 years ago. The rings suggest that Earth was blasted with a period of solar activity so extreme that traces of the event could still be seen in the carbon signature of tree rings. A team of researchers led by Nagoya University in Japan claim that dating back to 5480 b. c. there was an unprecedented shift in the Sun’s magnetic activity, a shift the like of which has

Tree Rings

221

not happened since in human history. As we now know, the Sun’s activity is centered around an 11-year cycle, with the Sun becoming increasingly active and unleashing more solar storms and flares about halfway through the cycle, before falling relatively silent again. However, 7000  years ago, something occurred that was certainly not part of the cycle, an event that would make Douglass’ supposed link between solar activity and climatic conditions a matter for serious reconsideration. The team found evidence to suggest that a mysterious ‘solar event’ took place, making this conclusion while looking at the amount of the carbon-14 isotope in the rings of an ancient bristlecone pine tree. Carbon-14, or radiocarbon, is a radioactive isotope of carbon, its presence in organic materials the basis of the radiocarbon dating method, pioneered by chemist Willard Frank Libby (1908–1980). Libby, who won the Nobel Prize in Chemistry in 1960, made significant contributions to not only the development of the radiocarbon dating method while studying the science at the then newly formed Institute for Nuclear Studies at the University of Chicago. In 1939, Serge Alexander Korff (1906–1989) had discovered that cosmic rays generated neutrons in the upper atmosphere, these interacting with nitrogen-14 in the air to produce carbon-14. Korff, a pioneer in the study of cosmic ray neutrons, along with his passion as an inventor and explorer, cataloged cosmic ray-­ produced neutrons in the high atmosphere from balloons and rockets launched across the globe. It is said that upon Korff’s passing he left many legacies, among which were a so-called generation of astrophysicists who proudly referred to themselves as Korff’s balloonatics! Libby analyzed Korff’s findings and realized that when plants and animals die, they cease to ingest fresh carbon-14, thereby giving any organic compound a built-in nuclear clock. In 1949, it occurred to Libby that the amount of carbon-14 decay found in animal or plant could be used as a gauge of how long it had been dead. Carbon-14 has a half-life of 5730 years. That meant if Libby found a sample where the amount of carbon-14 was only half the amount that might be expected in a living creature, he knew the age of it would be about 5730 years. Libby published his theory in 1946, expanding on it in a monograph entitled Radiocarbon Dating in 1955. It was a technique that in later years was to revolutionize archaeology, paleontology, and other disciplines that dealt with ancient artifacts.

222

11.  Fossils, Tree Rings, and Ice

The synthesis of the isotope carbon-14 was discovered on February 27, 1940, by chemists Martin David Kamen (1913–2002) and Sam Ruben (1913–1943), at the University of California Radiation Laboratory in Berkeley. By bombarding matter with particles in the cyclotron, radioactive isotopes such as carbon-14 were ­generated. Using carbon-14, the order of events in biochemical reactions could be elucidated, showing the precursors of a particular biochemical product, revealing the network of reactions that constitute life. The very existence of carbon-14 was suggested by Franz Newell Devereux Kurie (1907–1972) in 1934. Kurie, an American physicist, was most famous for showing that the neutron was neither a dumbbell-shaped combination of a proton and electron nor an onion-shaped combination of an electron embracing a proton. Consequently, and until the discovery of the quark structure of hadrons, the neutron was assumed to be an elementary particle. Could the work of so many scientists spanning decades of research shed light on a strange solar occurrence just by the examination of the tree rings of a California bristlecone tree? Firstly, though, why the bristlecone pine? The term bristlecone pine covers three species of the pine tree family; all three are long-lived and highly resilient to harsh weather and bad soils. One of the three species, Pinus longaeva, is among the longest-lived life forms on Earth. The bristlecone pine, so-called because of its prickles on female cones, tends to grow in scattered subalpine groves at high altitude in arid regions of the western United States and is such a tough tree that its wood can survive intact for a long time after it is dead. During its potentially long lifetime, the bristlecone pine sucks up atmospheric carbon, storing the carbon within its rings each year of its life. When solar activity is weak, the amount of carbon-­14 in the atmosphere increases. When the team analyzed this particular pine, they saw uniquely high amounts of carbon-14 in the rings that they dated back to the year 5480 b. c., indicating a new type of solar event. In order to ensure the reliability of findings, measurements of carbon-14 levels in the bristlecone pine were examined at three different laboratories, one in Japan, the other two in the United States and Switzerland, respectively. Making comparisons with other tree-ring records, only two more events were found to be anywhere near similar, though both were less intense. One of the team members, A.J.  Timothy Jull, a radiocarbon scientist from

Tree Rings

223

the University of California, confirmed that bar two other cosmic ray events in a. d. 775 and 994, the newly discovered carbon-14 change identified in the tree rings was more abrupt and the most dramatic by far. The cause of the strange solar activity in 5480 b. c. remains a topic of debate, but the team, when drawing comparisons to the events of a. d. 775 and 994, respectively, could point to either a very weak Sun or a series of repeated, strong solar flares. Professor Fusa Miyake, lead researcher from Nagoya University, speculated that a change in magnetic activity of the Sun accompanied by strong solar bursts may account for the carbon-14 data seen in the tree rings. What we learned about the bristlecone pine tree is paralleled by the examination of Japanese cedar trees, these yielding the data behind an observed increase of 1.2% in the concentration of carbon-­14 in tree rings dating back to the year a. d. 775, one of the other two significant events. These cedar trees are large, evergreen trees, endemic to Japan, where they are also known as Japanese sugi pine, or Japanese red cedar in English. The timber from the tree is weather and insect resistant. The increase, which is about 20 times as high as the normal background rate of variation, is supported by a surge in another isotope, that of beryllium, which was detected in Antarctic ice cores associated with the event of 775. The event and associated carbon-14 levels found in the Japanese cedar trees appears to have been globally recorded, with the same signals discovered in tree rings in Germany, Russia, the United States, and New Zealand. Several hypotheses exist as to the nature and cause of the a. d. 775 event. The Anglo-Saxon Chronicle makes reference to a “red crucifix” seen after sunset in 775. The interpretation was thought to point to that of a supernova, but since no remnant of such an occurrence has been found for that year, a more plausible explanation is that of aurora borealis. This is mirrored by a reference made in China to an aurora recorded on January 12, 776, the only reference of its type from the mid-770 s. However, though close, it does not account for what was seen in 775, with the only possible corresponding reference made being one concerning a thunderstorm. However, and probably most likely, the event can be explained by the occurrence of an SPE (solar particle event), whereby a very strong solar flare is launched from the Sun’s surface, or an even more extreme event, that of a gamma-ray burst.

224

11.  Fossils, Tree Rings, and Ice

The a. d. 775 event remains the strongest spike in the record for cosmogenic isotopes, a period of records that spans some 11,000 years, with the event of 994 not as strong. Even if the event of 775 was a gamma-ray burst, it did not cause any catastrophic happenings on Earth. However, as no technology above the atmosphere, manned or unmanned, was around at the time, there may well be a different effect were a similar occurrence to happen in modern times. Power supplies, satellites, and communications would be subjected to a force that may well cause them great disruption.

Comet Impact or Supervolcano? Could the explosion of a comet in Earth’s atmosphere have contributed to the collapse of the Roman Empire in the West and ushered in the Dark Ages? Studies of tree rings dating back thousands of years have shown that the world experienced a sudden and catastrophic drop in temperatures in a. d. 540. According to tree ring expert at Queen’s University Belfast, Professor Emeritus of Paleoecology Michael Baillie, the scale of the disaster would have led to repeated crop failures, famines, and the spread of bubonic plague, responsible for wiping out around a third of the population of Europe. Baillie, an expert in dendrochronology, proposed upon examining tree rings that there were correlations between the rings and environmental downturns around 2354 b. c., 1628 b. c., 1159 b. c., 208 b. c., and a. d. 540 – the latter ushering in the Dark Ages and the fall of the Roman Empire. The plague of a. d. 542, triggered by 2  years of famines and bad harvests, also may have hindered the attempts of the Roman Emperor Justinian I to reconquer Western Europe, altering the political make-up of Europe. Baillie suggested that the studies of tree-ring chronologies from trees in Siberia, throughout Europe and North and South America, coincided with the second largest ammonium signal discovered in the Greenland ice in the last two millennia, the largest being in a. d. 1014. Ammonia and other parent molecules have long been associated with comets, with an icy nucleus made of varying amounts of water, carbon dioxide, ammonia, and methane. Perhaps, though, and more than just a coincidence, both ammonium signals occurred during heightened cometary-type activity. Around A. d, 400–600, there is evidence to suggest that there was an increased risk of cometary debris bombardment, based on fireball activity in the Taurid meteor stream, as recorded

Tree Rings

225

in Chinese and Mediterranean archives. A comet, or cometary fragments from the stream, could well have exploded in the atmosphere, surrounding the globe with a cloud of dust and water vapor. The explosion or sequence of explosions high in the atmosphere, as seen in 1994, when fragments Shoemaker-Levy 9 plowed into Jupiter, would, aside from blotting out sunlight, cause a significant climatic shift. The evidence could relate to a stream of cosmic debris, or a singular event, with a comet the size of Hale-Bopp involved. Hale-­ Bopp was one of the most widely observed comets of the twentieth century, visible to the naked eye for a record 18 months, and dubbed as the Great Comet of 1997. Its nucleus had an estimated diameter of between 30–40 km in diameter. However well-supported the argument might be, there still remains no impact crater that has been linked to an event around 540 onwards for several years. Despite much of the seabed being scrutinized by survey equipment, nothing had come to light. A counter challenge to an impact is that the comet or debris may have been destroyed in an airburst, scattering fragments far and wide with no attributable singular impact crater. In a challenge to the comet theory, other scientists have suggested a supervolcano or series of large volcanoes may be responsible, generating great plumes of dust that upon entering the atmosphere, encircled Earth, throwing the planet into a state of perpetual twilight. The supervolcano theory, though, has several problems associated with its proposed impact on a global scale. Firstly, and probably most damningly, no such record exists to support the presence of a volcano or series of volcanoes at this time, none that has been satisfactorily correlated as instigator of the event. Secondly, a volcano of such magnitude would produce a significant amount of acidity in the atmosphere, which in turn would be recorded in the polar ice caps. Numerous ice-core studies have been carried out in both Greenland and Antarctica, and none of these have found evidence for an acid layer around a. d. 536 of the sort that would be caused by the eruption of a supervolcano. Although some evidence was discovered, small acid layers that have been linked with 528 and 533, they were not sufficiently strong that they could be related to a large volcanic episode. Thirdly, of the five known surviving reports for the event, none of them offers an eruption as an explanation. At best, vague terminology is used in terms of an unusual Sun dimming or

226

11.  Fossils, Tree Rings, and Ice

a­ tmospheric veiling. Chinese accounts refer to obscured skies and summer frosts. Mediterranean historians also recording a “dry fog” event, which dimmed sunlight, describing the event as 12 or perhaps 18 months in duration. This length of time would appear to be too short when comparing the effects of the event on a global scale, which is thought to have lasted up to a decade. The Roman statesman, scholar of antiquity, and writer Cassiodorus (485–585) describes a dim Moon, and a Sun that lost its “wonted light” and appeared “bluish,” as if in “transitory eclipse throughout the whole year.” Strangely, and probably without worthy connection, the “bluish” appearance of the Moon can be caused by smoke or dust particles in the atmosphere, as happened after the forest fires in Sweden and Canada in 1950 and 1951, respectively. Also, following the eruption of Krakatoa in 1883, the Moon appeared blue for 2 years. Other less potent volcanoes have also resulted in turning the Moon a shade of blue: Mount St Helens in the state of Washington in 1980; El Chichon in Mexico in 1982; and Mount Pinatubo, located on the tripoint boundary of the provinces of Zambales, Tarlac, and Pampanga, in 1991. Other segments of data that collectively show a period of atmospheric change relating to an event that starts around a. d. 536 lasting until 540. Tree rings salvaged from Irish peat bogs indicate a series of colder than average summers at this time. Overall, the year 536 is noted as one of the coldest 2 or 3 years globally in the last 2000 years. Fennoscandia pine trees reflect a similar effect, with a correlation found in European oak tree data, all showing typical variations in tree-ring widths. Further tree ring analysis of bristlecone and foxtail pines in North America, along with Mongolian tree rings and Argentinian tree rings, offered convincing data. Decreases in the rate of ring tree growth corresponds to a global temperature decrease of −3 degrees C. Whatever the cause, volcano or comet strike, tree rings have provided perhaps an unusual record of past events, a record penned by Mother Nature herself.

Ice Just as tree rings record and encapsulate past events in the wood, ice, too, can be a great preserver of past events, entombing segments of history within its freezer – a perfect way to capture an

Ice

227

event of the time and hold it as though, when released, not a day has passed. During the Pleistocene, Earth was in the process of warming up, with temperatures slowly rising and glaciers retreating. However, an event occurred that triggered a cold snap substantial enough to leave its mark on the geological record – an event that saw Earth cool again, somewhere between 3–11 degrees Fahrenheit. Known as the Younger Dryas (named after a flower Dryas octopetala that grows in cold conditions and became common in Europe during this time), there has been much speculation as to its cause. The Younger Dryas (12,900–11,700) was a return to glacial conditions that temporarily reversed the gradual climate warming that was taking place after the Last Glacial Maximum (LGM). The last LGM saw ice sheets at the greatest extent, covering much of North America, northern Europe, and Asia. The impact on Earth’s climate was significant, causing drought, desertification, and a large drop in sea levels. Occurring at the end of the Pleistocene epoch and immediately before the current, warmer Holocene epoch, the Younger Dryas denotes the most recent and longest of several interruptions to the gradual warming over Earth’s climate since the severe Last Glacial Maximum. Was the Younger Dryas event the result of an asteroid strike perhaps, or volcanic activity, or some sort of massive freshwater flood that temporarily disrupted climate cycles based out of the North Atlantic? Although all are plausible, the lack of a meteorite crater meant that this particular hypothesis fell flat. However, work conducted by Professor Kurt Kjaer from the Natural History Museum of Denmark and University of Copenhagen, uncovered a 31-km-wide crater that could alter opinions on the trigger for the Younger Dryas event. Located 240 km from Thule Air Base, the United States’ northernmost Air Force base, researchers believe the crater is between three million and 12,000 years-old, placing it in the Pleistocene. Interestingly, Thule Air Base is located 1207 km north of the Arctic Circle, and 1524 km from the North Pole, on the northwest coast of Greenland. Thule’s arctic environment includes icebergs in North Star Bay, two islands (Saunders Island and Wolstenholme Island), a polar ice sheet, and Wolstenholme Fjord, the only place on Earth where four active glaciers join together. The impact crater lies beneath the Hiawatha Glacier in northwest Greenland, near Inglefield Land. It was originally mapped in

228

11.  Fossils, Tree Rings, and Ice

1922 by Danish geologist and arctic explorer Lauge Koch (1892– 1964), who noted that the glacier tongue extended into Lake Alida (near Foulk Fjord). Koch was a renowned leader of no fewer than 24 Danish government expeditions to Greenland. The discovery of the impact crater was by chance, as Kjaer and other members of a research team were in Greenland on other work, mapping arctic sea ice with NASA’s IceBridge project when they happened to stumble upon it. During the various airborne surveys undertaken to map the thickness of the ice, the crater became apparent, deep under the Hiawatha glacier. The crater appears as a circular bedrock depression, locked away beneath a kilometer of ice. From the interpretation of the crystalline nature of the underlying rock, together with chemical analysis of sediment washed from the crater, the impactor could well have been an iron meteorite with a diameter of 1.5 km. A volume of approximately 20 cu. km of rock would have been vaporized or melted. Should the impact crater be proven to be that of an asteroid or equivalent, it would be one of the 25 largest known impact craters on Earth. It has been suggested that the impact was only part of the reason behind the Younger Dryas event, merely the trigger for the other proposed explanation. Because of the crater’s location on the ice sheet, it is possible that the impact could have in turn caused exactly the kind of massive influx of freshwater to the North Atlantic that has been touted. An asteroid hitting an ice sheet could spawn a number of water-related effects, meaning that the actual strike was just the start of a sequence of events that incorporated more than just the impact itself. Before the discovery of the crater, other finds of significance were made, begging the question as to whether the creator of the large impact crater had company as it plowed through Earth’s atmosphere. Did it fragment, scattering the region with debris? The Inuit, indigenous peoples inhabiting the arctic regions of Greenland, Canada, and Alaska, found iron meteorites in the region. In 1957, an American surveyor found a 48-kg meteorite, and on July 31, 1963, metallurgist Vagn Fabritius Buchwald found the 20-ton Agpalilik meteorite (a fragment of the Cape York meteorite, and often referred to as ‘the Man’), on a nunataq (ridge or peak covered with ice and snow) near Moltke glacier, on the Agpalilik peninsula in the Thule district of northwest Greenland. It has been suggested that the Cape York meteorite was part of the main object that made the Hiawatha crater.

Antarctic Impacts

229

Cape York is a cape on the northwestern coast of Greenland, in northern Baffin Bay. In Greenlandic language, the name of the settlement Savissivik on the island close to the cape means “place of meteorite iron” (savik meaning iron or knife), alluding to the numerous meteorites from 10,000 years ago that have been found there, including the Cape York meteorite. With an estimated total weight of 58,200 kg, the Cape York meteorite is one of the largest meteorites in the world. The ice, though, conceals many other impacts. Nearby to the Hiawatha crater, a second unrelated crater has been discovered measuring 36-km wide, and like the Hiawatha crater, though seemingly obvious to some quarters of the scientific community, has not been definitively identified as an impact crater. Despite the discovery in the Hiawatha crater of minerals that appear to have been abruptly shocked by a dramatic event such as a meteorite impact, speculation remains. Situated 183 km southeast of the Hiawatha crater, this second impact contains the same distinctive rim and interior peaks as the other, with the impact structure formed more than 79,000 years ago, before any of the ice currently above the crater was in place.

Antarctic Impacts Gravity maps of the Antarctic continent have shown the possibility of multiple impact sites. Anomalies in readings mark spots where, hundreds of thousands of years ago, the frozen continent was struck by a succession of bodies, and in particular with regard to the Wilkes Land ice sheet, a giant singular impact. The anomalies discern themselves by reflecting slightly lower gravity readings, the result of fragments that have penetrated deep into the crust and shattered the rock. This could be interpreted as small singular strikes spread over a large area, or in the case of a much more substantial impact, that of a single body. First proposed by R.  A. Schmidt in 1962, geophysicist Dr. John G. “Jack” Weihaupt (1930–2014), from the University of Colorado, further hypothesized in a detailed paper in 1976 that a large ­negative gravity anomaly measuring at 234  km across and 848  m deep could have been the result of an asteroid or comet strike. Despite challenges to the claim, the Wilkes Land Anomaly has been classified as a “probable impact crater.” The Wilkes Land mass concentration (mascon) was first reported at a conference in May 2006 by a team of researchers led

230

11.  Fossils, Tree Rings, and Ice

by American geophysicist Ralph von Frese and American scientist Laramie Potts from Ohio State University. Using data collected by NASA’s GRACE satellites, they identified a 300-km-wide mass. The GRACE (Gravity Recovery and Climate Experiment) satellites were a joint mission between NASA and the German Aerospace Center. Twin satellites took detailed measurements of Earth’s gravity field anomalies. The mission, which was launched in March 2002 and concluded in October 2017, set out to measure these anomalies in order to discover how mass is distributed around the planet, and how it varies over time. The mass anomaly is centered within a larger ring-like shape visible in radar images of the land surface below the Antarctic ice cap. This combination suggested to von Frese and Potts that the feature may mark the site of a 480-km impact crater, buried beneath the ice. The crater measured 2.5 larger than the 180-kmr-­ wide Chicxulub crater, buried underneath the Yucatan Peninsula in Mexico, the center located near the town of Chicxulub, after which the crater is named. That was formed by a large asteroid or comet measuring 11–81 km in diameter. Due to the siting of the find made by von Frese and Potts, there are no direct samples to test for evidence of impact. Estimated to be around 500  million years old, further discussion ensued that such was the impact that it might have instigated the breakup of the so-called Gondwana supercontinent, which pushed Australia northward. Gondwana was an ancient supercontinent that broke up about 180  million years ago. The continent eventually split into the landmasses we recognize today: Africa, South America, Australia, Antarctica, the Indian subcontinent, and the Arabian Peninsula. The early version of Gondwana joined with the other landmasses on Earth to form the single supercontinent Pangaea by about 300 million years ago. Around 280–230  million years ago, though, Pangaea started to split. Magma from below Earth’s crust began pushing upwards, creating a fissure between what would become Africa, South America, and North America. As part of this process, Pangaea cracked into a northernmost and southernmost supercontinent. The northern landmass, Laurasia, would drift north and gradually split into Europe, Asia, and North America. The southern landmass, still carrying those bits and pieces of the future southern hemisphere, headed southward after the split. This was Gondwana.

Supernovae

231

Supernovae In 2001, a team of Japanese scientists drilled a 122-m ice core sample at the Dome Fuji station, an inland site in Antarctica. At a depth of about 50  m, corresponding with the eleventh century, they found three nitrogen oxide spikes, two of which were 48 years apart and easily identifiable as belonging to two supernova outbursts, SN 1006 and SN 1054. The team speculated that the third spike could be related to another supernova, visible only from the southern hemisphere. Additionally, the team saw a ten-year variation in the background levels of nitrogen oxide, almost certainly caused by the solar cycle, an effect that has been seen before in ice cores. This is one of the first times that a distinct 11-year solar cycle has been observed for a period before the landmark studies of sunspots conducted by Galileo. This is another thread running through the history of how astronomical observations have been recorded, with Galileo at the telescope eyepiece, and, centuries later, the results of a solar cycle found deep in Antarctic ice. The thread’s own twine incorporates two vastly different aspects of observing and collating evidence of the existence of the very same phenomena. Nature capturing moments in history and preserving them for reference in the future, just as a writer’s words embellish a page, or a pixel of data is incorporated on a computer image taken of a far distant galaxy, all reference points to the various and diverse ways in which phenomena in the universe have been recorded and stored throughout the centuries.

Glossary Absolute magnitude Brightness of a star or celestial object if seen from a standard distance of 10 parsecs. Achondrite A stony meteorite lacking chondrules. Albedo The ratio of the light reflected in all directions by a surface to the light incident on it. A perfectly reflecting surface has an albedo of 1, a perfectly absorbing surface has an albedo of 0. Altitude The angular distance between the direction to an object and the horizon. Altitude ranges from 0 degrees for an object on the horizon to 90 degrees for an object directly overhead. Altazimuth mount The simplest type of telescopic mount with two motions, altitude (vertical) and azimuth (horizontal). Amor asteroid A member of a class of asteroids who orbits cross Earth’s orbit. Angular momentum The momentum of a body associated with its rotation or revolution. For a body in a circular orbit, angular momentum is the product of orbital distance, orbital speed, and mass. When two bodies collide or interact, angular momentum is conserved. Annular eclipse A solar eclipse in which the Moon is too far from the Earth to block the entire Sun from view and a thin ring of sunlight appears around the Moon. Aperture The diameter of the main light-gathering lens or mirror, given in inches, centimeters, or meters. © Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4

233

234

Glossary

Apex The direction in the sky toward which the Sun is moving. Because of the Sun’s motion, nearby stars appear to diverge from the apex. Aphelion The point in the orbit of a Solar System body where it is farthest from the Sun. Apogee The point in an orbit of Earth that is furthest from the Sun. Apollo asteroid A member of a class of asteroids whose orbits cross the orbit of Earth. Apparent magnitude Brightness of a star or celestial object when observed at its great distance from Earth. Asteroid A small, planet-like Solar System body. Most asteroids are rocky in makeup and have orbits of low eccentricity and inclination. Asteroid Belt The region of the Solar System lying between 2.1 and 3.3 AU from the Sun. The great majority of asteroids are found in the Asteroid Belt. Astronomical unit (AU) The mean Earth-Sun distance, about 150,000,000 km. Aten asteroid An asteroid having an orbit with a semi-major axis smaller than 1 AU. Atom A particle consisting of a nucleus and one or more surrounding electrons. Aurora Australis Light emitted by atoms and ions in the upper atmosphere near the south magnetic pole. The emission occurs when atoms and ions are struck by energetic particles from the Sun. Aurora Borealis Light emitted by atoms and ions in the upper atmosphere near the north magnetic pole. The emission occurs when atoms and ions are struck by energetic particles from the Sun.

Glossary

235

Axis The imaginary line that an object, usually a planet, rotates around. Azimuth The angular distance between the northern point on the horizon eastward to the point on the horizon nearest the direction to a celestial body. Bailey’s beads Sunlight glimpsed through surface features around the limb of the Moon during a total solar eclipse. Also known as the diamond ring effect. Barred spiral galaxy A spiral galaxy in which the nucleus is crossed by a bar. The spiral arms start at the ends of the bar. Barycenter The center of mass of a system of bodies. Big Bang The theory that suggests that the universe was formed from a single point in space during a cataclysmic explosion. Big Crunch The theory that states that the universe will expand to its maximum point, then contract until it explodes. Big Rip The theory that states that all matter under the continued expansion of the universe will eventually rip the universe apart. Black hole A region of space from which no matter or radiation can escape. A black hole is a result of the extreme curvature of space by a massive compact body. Bolide A term used to describe an exceptionally bright meteor, possibly accompanied by a sonic boom. Bow shock The region where the solar wind is slowed as it impinges on Earth’s magnetosphere. Brightness Intensity of light received from a celestial object by the observer.

236

Glossary

C-type asteroid One of a class of very dark asteroids whose reflectance spectra show no absorption features, due to the presence of minerals. Capture theory An origin theory of the Moon that holds that it formed elsewhere in the Solar System and then was captured into orbit around Earth. Carbonaceous chondrite A stony meteorite that contains carbon-rich material. Carbonaceous chondrites are thought to be primitive samples of material from the early Solar System. Cassini’s division A conspicuous 1,800-km-wide gap between the outermost rings of Saturn. Celestial equator The circle where Earth’s equator, if extended outward into space, would intersect the celestial sphere. Celestial horizon The circle on the celestial sphere that is 90 degrees from the zenith. The celestial horizon is approximately the boundary between Earth and the sky. Celestial mechanics The part of physics and astronomy that deals with the motions of celestial bodies under the influence of their mutual gravitational attraction. Celestial poles The celestial poles are imaginary lines that trace Earth’s rotation axis in space. Celestial sphere An imaginary sphere surrounding Earth. The celestial bodies appear to carry out their motions on the celestial sphere. Centaurs Small astronomical bodies that generally orbit the Sun between Jupiter and Neptune. Centaurs cross the orbital paths of the major planets.

Glossary

237

Charge coupled device (CCD) An array of photosensitive electronic elements that can be used to record an image. CCD cameras are composed of silicon chips that are light sensitive, changing detected photons of light into electronic signals that in turn can be used to create images of astronomical objects. Chondrite A meteorite containing chondrules. Chondrule A small spherical body embedded in a meteorite. Chondrules are composed of iron, aluminium, and magnesium silicate rock. Chromosphere The part of the Sun’s atmosphere between the photosphere and the corona. Circumpolar stars Circumpolar stars never set or go below the horizon for observers from specific latitudes. Coma A spherical gaseous region that surrounds the nucleus of a comet. The coma of a comet may be 100,000 km or more in diameter. Comet A small, icy body in orbit around the Sun. When a comet is near the Sun, it displays a coma and a tail. Conjunction The appearance of two celestial bodies, often a planet and the Sun, in approximately the same direction. Constellation One of 88 regions into which the celestial sphere is divided. Continuous spectrum A spectrum containing neither emission nor absorption lines. Convection The process of energy transport in which heat is carried by hot, rising and cool, falling currents or bubbles of liquid or gas. Core The innermost region of the interior of Earth or another planet.

238

Glossary

Coriolis effect The acceleration which a body experiences when it moves across the surface of a rotating body. The acceleration results in a westward deflection of projectiles and currents of air or water when they move toward Earth’s equator and an eastward deflection when they move away from the equator. Corona The outermost layer of the Sun’s atmosphere. Gases in the corona are tenuous and hot. Coronal hole A low density, dim region in the Sun’s corona. Coronal holes occur in areas of open magnetic field lines, where gases can flow freely away from the Sun to form the solar wind. Coronal mass ejection A blast of gas moving outward through the Sun’s corona and into interplanetary space following the eruption of a prominence. Cosmic background radiation (CBR) Radiation observed to have almost perfectly uniform brightness in all directions in the sky. The CBR is highly redshifted radiation produced about a million years after the universe began to expand. Cosmic rays Extremely energetic ions and electrons that travel through space at almost the speed of light. Most cosmic rays come from great distances and may be produced in supernovas and pulsars. Cosmic string A tube-like configuration of energy that is believed to have existed in the early universe. Cosmology The study of the universe as a whole. Crater A roughly circular feature on the surface of a Solar System body caused by the impact of an asteroid or a comet. Crescent phase The phase of the Moon at which only a small, crescent-shaped portion of its near side is illuminated by sunlight. Crescent phase occurs just before and after new Moon.

Glossary

239

Critical density The value that the average density of the universe must equal or exceed if the universe is closed. If the density of the universe is less than the critical density, the universe will continue to expand forever. Crust The outermost layer of the interior of a planet or satellite. Dark energy A theoretical form of energy postulated to act in opposition to gravity. Dark matter Matter that cannot be detected or has not yet been detected by the radiation it emits. The presence of dark matter can be deduced from its gravitational interaction with other bodies. Declination The angular distance of a celestial body north or south of the celestial equator. Declination is analogous to latitude in the terrestrial coordinate system. Differential rotation Rotation in which the rotational period of a body varies with latitude. Differential rotation occurs for gaseous bodies such as the Sun or for planets with thick atmospheres. Differentiation The gravitational separation of the interior of a planet into layers according to density. When differentiation occurs inside a molten body, the heavier materials sink to the center and the light materials rise to the surface. Doppler effect The change in the frequency of a wave (such as electromagnetic radiation) caused by the motion of the source and observer toward or away from each other. Dust tail A comet tail that is luminous because it contains dust that reflects sunlight. The dust in a comet tail is expelled from the nucleus of the comet.

240

Glossary

Earthshine A dull glow that lights up the unlit part of the Moon because the Sun’s light reflects off Earth’s surface and back onto the Moon. Eclipse The obscuration of the light from the Sun when the observer enters the Moon’s shadow or the Moon when it enters Earth’s shadow. Also, the obscuration of a star when it passes behind its binary companion. Ecliptic The plane of Earth’s orbit around the Sun. As a result of Earth’s motion, the Sun appears to move among the stars, following a path that is also called the ecliptic. Electromagnetic wave A periodic electrical and magnetic disturbance that propagates through space and transparent materials at the speed of light. Light is an example of an electromagnetic wave. Electron A low-mass, negatively charged particle that can either orbit a nucleus as part of an atom, or exist independently as part of a plasma. Ellipse A closed, elongated curve describing the shape of the orbit that one body follows around another. Elliptical galaxy A galaxy having an ellipsoidal shape and lacking spiral arms. Elongation Angular distance of a celestial object from the Sun in the sky. Ephemeris A tabulation of the positions of a celestial object in sequence for a succession of dates. Equator The line around the surface of a rotating body that is midway between the rotational poles. The equator divides the body into northern and southern hemispheres. Equatorial jet The high-speed, eastward, zonal wind in the equatorial region of Jupiter’s atmosphere.

Glossary

241

Equatorial mount An equatorial telescope mount allows the observer to follow the rotation of the sky as Earth turns. Equatorial system A coordinate system, using right ascension and declination as coordinates, used to describe the angular location of bodies in the sky. Equinox Either of the two points on the celestial sphere where the ecliptic intersects the celestial equator. Escape velocity The speed that an object must have to achieve a parabolic trajectory and escape from its parent body. Event horizon The boundary of a black hole. No matter or radiation can escape from within the event horizon. Exosphere The outer part of the thermosphere. Atoms and ions can escape from the exosphere directly into space. Eyepiece The lens at the viewing end of a telescope. Fermi paradox The question that given the known size of the universe, why have we not been contacted and are still alone? Named after Italian physicist Enrico Fermi. Filament A dark line on the Sun’s surface when a prominence is seen projected against the solar disk. Fireball An especially bright streak of light in the sky produced when an interplanetary dust particle enters Earth’s atmosphere, vaporizing the particle and heating the atmosphere. Focal length The distance between a mirror or lens and the point at which the lens or mirror brings light to a focus.

242

Glossary

Focal plane The surface where the objective lens or mirror of a telescope forms the image of an extended object. Focal point The spot where parallel beams of light striking a lens or mirror are brought to a focus. Galactic bulge A somewhat flattened distribution of stars surrounding the nucleus of the Milky Way. Galactic disk A disk of matter containing most of the stars and interstellar matter in the Milky Way. Galactic equator The great circle around the sky that corresponds approximately to the center of the glowing band of the Milky Way. Galactic halo The roughly spherical outermost component of the Milky Way. Galactic nucleus The central region of the Milky Way. Galaxy A massive system of stars, gas, and dark matter held together by its own gravity. Gamma ray The part of the electromagnetic spectrum having the shortest wavelengths. Gegenschein A patch of very faint nebulous light sometimes seen in the night sky opposite the position of the Sun. Geosynchronous orbit An orbit in which a satellite's orbital velocity is matched to the rotational velocity of the planet. Globular cluster A tightly packed, spherically shaped group of thousands to millions of old stars.

Glossary

243

Granule A bright convective cell or current of gas in the Sun’s photosphere. Granules appear bright because they are hotter than the descending gas that separates them. Gravitational lens A massive body that bends light passing near it. A gravitational lens can distort or focus the light of background sources of electromagnetic radiation. Gravity The force of attraction between two bodies generated by their masses. Great Attractor A great concentration of mass toward which everything in our part of the universe is apparently being pulled. Greenhouse effect The blocking of infrared radiation by a planet’s atmospheric gases. Because its atmosphere blocks the outward passage of infrared radiation emitted by the ground and lower atmosphere, the planet cannot cool itself effectively and becomes hotter than it would be without an atmosphere. Habitable zone The range of distances from a star within which liquid water can exist on the surface of an Earth-like planet. Helioseismology A technique used to study the internal structure of the Sun by measuring and analyzing oscillations of the Sun’s surface layers. Heliosphere The region of space dominated by the solar wind and the Sun’s magnetic field. Hilda asteroids A group of asteroids with a 3:2 orbital resonance with Jupiter. Hubble’s law The linear relationship between the recession speeds of galaxies and their distances. The slope of Hubble’s law is Hubble’s constant.

244

Glossary

Hyperbola A curved path that does not close on itself. A body moving with a speed greater than escape velocity follows a hyperbola. Inclination The tilt of the rotation axis or orbital plane of a body. Inertia The tendency of a body at rest to remain at rest and a body in motion to remain in motion at a constant speed and in constant direction. Inertial motion Motion in a straight line at constant speed followed by a body when there are no unbalanced forces acting on it. Inferior planet A planet whose orbit lies inside Earth’s orbit. Infrared The part of the electromagnetic spectrum having wavelengths longer than visible light but shorter than radio waves. Interferometry The use of two or more telescopes connected together to operate as a single instrument. Interferometers can achieve high angular resolution if the individual telescopes of which they are made are widely separated. Interstellar matter Gas and dust in the space between the stars. Ion An atom from which one or more electrons has been removed. Ionization The removal of one or more electrons from an atom. Ionosphere The lower part of the thermosphere of a planet in which many atoms have been ionized by ultraviolet solar photons. Inferior conjunction A conjunction of an inferior planet that occurs when the planet is lined up directly between Earth and the Sun.

Glossary

245

Iron meteorite A meteorite composed primarily of iron and nickel. Isotopes Nuclei with the same number of protons but different numbers of neutrons. Jet Venting of gas from weak areas of a comet’s nucleus. Also, a narrow beam of gas ejected from a star or the nucleus of an active galaxy. Kardashev scale A method of measuring a civilization’s level of technological advancement, formulated by Russian astronomer Nikolai Kardashev. Kepler’s Laws of Planetary Motion Three laws, discovered by Kepler, that describe the motions of the planets around the Sun. Kinetic energy Energy of motion. Kinetic energy is given by one half the product of a body’s mass and the square of its speed. Kirkwood gaps Regions in the asteroid belt where a decreased number of asteroids are found, possibly the result of believed to be the result of gravitational interactions with Jupiter. Named after astronomer Daniel Kirkwood (1814-1895), who first observed these gaps. Kuiper Belt A region beyond Neptune within which a large number of comets are believed to orbit the Sun. Short period comets are thought to have originated in the Kuiper Belt. Lagrangian points Positions in an orbital configuration where a small body, under the gravitational influence of two larger ones, will remain approximately at rest relative to them. Named after 18th century Italian astronomer and mathematician Joseph-Louis Lagrange. Latitude The angular distance of a point north or south of the equator of a body as measured by a hypothetical observer at the center of a body.

246

Glossary

Lava Molten rock at the surface of a planet or satellite. Light The visible form of electromagnetic radiation. Light curve A plot of the brightness of a body over time. Light year A unit of length equal to the distance that light travels in one year in a vacuum, about 9.46 trillion km. Limb The apparent edge of the disk of a celestial body. Lithosphere The rigid outer layer of a planet or satellite, composed of the crust and upper mantle. Local Group The small cluster of galaxies of which the Milky Way is a member. Longitude The angular distance around the equator of a body from a zero point to the place on the equator nearest a particular point as measured by a hypothetical observer at the center of a body. Luminosity The rate of total radiant energy output of a body. Luminosity class The classification of a star’s spectrum according to luminosity for a given spectral type. Luminosity class ranges from ‘I’ for a supergiant to ‘V’ for a dwarf (main sequence star). Luminosity function The distribution of stars or galaxies according to their luminosities. A luminosity function is often expressed as the number of objects per unit volume of space that are brighter than a given absolute magnitude or luminosity. Lunar eclipse The darkening of the Moon that occurs when the Moon enters Earth’s shadow.

Glossary

247

Lunation A lunation or synodic month is the average time from one new Moon to the next. M-type asteroid One of a class of asteroids that have reflectance spectra like those of metallic iron and nickel. Magellanic Clouds Two irregular galaxies that are among the nearest neighbors of the Milky Way. Magma Molten rock within a planet or satellite. Magnetosphere The outermost part of the atmosphere of a planet, within which a very thin plasma is dominated by the planet’s magnetic field. Magnitude A number, based on a logarithmic scale, used to describe the brightness of a star or other luminous body. Apparent magnitude describes the brightness of a star as we see it. Absolute magnitude describes the intrinsic brightness of a star. Mantle The part of a planet lying between its crust and its core. Maria A dark, smooth region on the Moon formed by flows of basaltic lava. Mass A measure of the amount of matter a body contains. Mass is also a measure of the inertia of a body. Maunder minimum A period of few sunspots and low solar activity that occurred between 1640 and 1700. Mean Solar Time Time kept according to the average length of the solar day. Meridian The circle on the celestial sphere that passes through the zenith and both celestial poles.

248

Glossary

Mesosphere The layer of a planet’s atmosphere above the stratosphere. The mesosphere is heated by absorbing solar radiation. Messier objects List of deep sky objects compiled by comet-hunter Charles Messier, who was looking for objects that were not comets. Metallic hydrogen A form of hydrogen in which the atoms have been forced into a lattice structure typical of metals. In the Solar System, the pressures and temperatures required for metallic hydrogen to exist only occur in the cores of Jupiter and Saturn. Meteor A streak of light produced by a meteoroid moving rapidly through Earth’s atmosphere. Friction vaporizes the meteoroid and heats atmospheric gases along the path of the meteoroid. Meteor shower A temporary increase in the normal rate at which meteors occur. Meteor showers last for a few hours or days and occur on about the same date each year. Meteorite The portion of a meteoroid that reaches Earth’s surface. Meteoroid A solid interplanetary particle passing through Earth’s atmosphere. Microlensing event The temporary brightening of a distant object that occurs because its light is focused on Earth by the gravitational lensing of a nearer body. Micrometeorite A meteoritic particle less than a 50 millionths of a meter in diameter. Micrometeorites are slowed by atmospheric gas before they can be vaporized, so they drift slowly to the ground. Milky Way The galaxy to which the Sun and Earth belong. Part of it seen as a pale, glowing band across the sky. Minor planet Another name for asteroid.

Glossary

249

Molecular cloud A relatively dense, cool interstellar cloud in which molecules are common. Momentum A quantity, equal to the product of a body’s mass and velocity, used to describe the motion of the body. When two bodies collide or otherwise interact, the sum of their momenta is conserved. Near-Earth asteroid (NEAR) or Near Earth Object (NEO) Bodies whose orbit comes into close proximity with Earth. Neutrino A particle with no charge and probably no mass that is produced in nuclear reactions. Neutrinos pass freely through matter and travel at or near the speed of light. Neutron star A star composed primarily of neutrons and supported by the degenerate pressure of the neutrons. Neutronization A process by which, during the collapse of the core of a star, protons and electrons are forced together to make neutrons. Noctilucent clouds Cloud-like phenomenon in the upper atmosphere of Earth caused by the presence of ice crystals. Also known as “night shining.” North celestial pole The point above Earth’s North Pole where Earth’s polar axis, if extended outward into space, would intersect the celestial sphere. Nova An explosion on the surface of a white dwarf star in which hydrogen is abruptly converted into helium. Nucleus An irregularly shaped, loosely packed lump of dirty ice or rock several kilometers across that is the permanent part of a comet. Objective The main lens or mirror of a telescope. Occultation An event that occurs when one celestial body conceals or obscures another.

250

Glossary

Oort Cloud The region beyond the planetary system, extending to 100,000 AU or more, within which a vast number of comets orbit the Sun. When comets from the Oort Cloud enter the inner Solar System, they become new comets for us. Opposition The configuration of a planet or other body when it appears opposite the Sun in the sky. Orbit The elliptical or circular path followed by a body that is bound to another body by their mutual gravitational attraction. Organic molecule A molecule containing carbon. Oscillating universe A theory that the universe goes through continual phases of expansion and contraction. Outgassing The release of gas from the interior of a planet or satellite. Ozone A molecule consisting of three oxygen atoms. Ozone molecules are responsible for the absorption of solar ultraviolet radiation in Earth’s atmosphere. Parabola A geometric curve followed by a body that moves with a speed exactly equal to escape velocity. Parallax A shift in the direction of a star caused by the change in the position of Earth as it moves around the Sun. Parsec A unit of distance equal to about 3.26 light years. Penumbra The outer part of the shadow of a body where sunlight is partially blocked by the body. Perigee The point, in an orbit around Earth, that is nearest to Earth.

Glossary

251

Perihelion The point in the orbit of a body when it is closest to the Sun. Perturbation A deviation of the orbit of a Solar System body from a perfect ellipse due to the gravitational attraction of one of the planets. Photon A massless particle of electromagnetic energy. Photometry The measurement of the light being emitted from astronomical objects. Photosphere The visible region of the atmosphere of the Sun or another star. Planetesimal A primordial Solar System body of intermediate size that accreted with other planetesimals to form planets and satellites. Plasma tail A narrow, ionized comet tail pointing directly away from the Sun. Plate tectonics Theoretical explanation describing the movement of seven large plates and a number of smaller plates of Earth’s lithosphere. Potentially hazardous asteroid (PHA) One of a group of asteroids that carry a collision potential with Earth. Precession The slow, periodic, conical motion of the rotation axis of Earth or another rotating body. Prominence A region of cool gas embedded in the Sun’s corona. Prominences are bright when seen above the Sun’s limb, but appear as dark filaments when seen against the Sun’s disk. Proper motion The rate at which a star appears to move across the celestial sphere with respect to very distant objects.

252

Glossary

Protein A large molecule, consisting of a chain of amino acids that make up the bodies of organisms. Protostar A star in the process of formation. Pulsar A rotating neutron star with beams of radiation emerging from its magnetic poles. When the beams sweep past Earth, we see “pulses” of radiation. Quantum mechanics The branch of physics dealing with the structure and behavior of atoms and their interaction with light. Quasar A distant galaxy, seen as it was in the remote past, with a very small, luminous nucleus. Radial velocity The part of the velocity of a body that is directed toward or away from an observer. The radial velocity of a body can be determined by the Doppler shift of its spectral lines. Radiant The point in the sky from which the meteors in a meteor shower seem to originate. Radio galaxy A galaxy that is a strong source of radio radiation. Radioactivity The spontaneous disintegration of an unstable nucleus of an atom. Reflectivity The ability of a surface to reflect electromagnetic waves. The reflectivity of a surface ranges from 0% for a surface that reflects no light to 100% for a surface that reflects all the light falling on it. Reflector A telescope in which the objective is a mirror. Refractor A telescope in which the objective is a lens.

Glossary

253

Regolith The surface layer of dust and fragmented rock, caused by meteoritic impacts, on a planet, satellite, or asteroid. Resolution The ability of a telescope to distinguish fine details of an image. Resonance The repetitive gravitational tug of one body on another when the orbital period of one is a multiple of the orbital period of the other. Retrograde motion The westward revolution of a Solar System body around the Sun. Right ascension Angular distance of a body along the celestial equator from the vernal equinox eastward to the point on the equator nearest the body. Right ascension is analogous to longitude in the terrestrial coordinate system. Roche limit or Roche radius The distance from a planet or other celestial body within which tidal forces from the body would disintegrate a smaller object. Term formulated by French mathematician Édouard Roche. S-type asteroid One of a class of asteroids whose reflectance spectra show an absorption feature due to the mineral olivine. Seismic wave Wave that travels through the interior of a planet or satellite and is produced by an earthquake or its equivalent. SETI (Search for Extra-Terrestrial Intelligence) NASA-led project to search for extra-terrestrial intelligent life. Sidereal clock A clock that marks the local hour angle of the vernal equinox. Solar constant The solar energy received by a square meter of surface oriented at right angles to the direction to the Sun at Earth’s average distance (1 AU) from the Sun. The value of the solar constant is 1,372 watts per square meter.

254

Glossary

Solar flare A brief, sudden brightening of a region of the Sun’s atmosphere, probably caused by the abrupt release of magnetic energy. Solar maximum Period of greatest solar activity in the 11-year solar cycle. Solar minimum Period of least solar activity in the 11-year solar cycle. Spectral class A categorization, based on the pattern of spectral lines of stars, that groups stars according to their surface temperatures. Spectrograph A device used to produce and record a spectrum. Spectroscopy The recording and analysis of spectra. Spicule A hot jet of gas moving outward through the Sun’s chromosphere. Spiral arm A long, narrow feature of a spiral galaxy in which interstellar gas, young stars, and other young objects are found. Spiral galaxy A flattened galaxy in which hot stars, interstellar clouds, and other young objects form a spiral pattern. Star A massive gaseous body that has used, is using, or will use nuclear fusion to produce the bulk of the energy it radiates into space. Starburst galaxy A galaxy in which a very large number of stars have recently formed. Steady state theory A cosmological theory in which the universe always remains the same in its essential features, such as average density. In order to maintain constant density while expanding, the steady state theory required the continual creation of new matter. Stellar occultation The obstruction of the light from a star when a Solar System body passes between the star and the observer.

Glossary

255

Stellar parallax The shift in the direction of a star caused by the change in the position of Earth as it moves around the Sun. Stellar population Stars that are similar in spatial distribution, chemical composition, and age that form a group. Stony meteorite A meteorite made of silicate rock. Stony-iron meteorite A meteorite made partially of stone and partially of iron and other metals. Stratosphere The region of the atmosphere of a planet immediately above the troposphere. Sun dog An atmospheric optical phenomenon that consists of a bright spot to the left or right of the Sun, or equally together. Sunspot A region of the Sun’s photosphere that appears darker than its surroundings because it is cooler. Sunspot cycle The regular waxing and waning of the number of spots on the Sun. The amount of time between one sunspot maximum and the next is about 11 years. Sun pillar An atmospheric optical phenomenon whereby a shaft of light is seen extending upward or downward from the Sun. Superior conjunction A conjunction that occurs when a planet passes behind the Sun and is on the opposite side of the Sun from Earth. Supernova An explosion in which a star’s brightness temporarily increases by as much as a billion times. Type I supernovas are caused by the rapid fusion of carbon and oxygen within a white dwarf. Type II supernovas are produced by the collapse of the core of a star.

256

Glossary

Synchronous rotation Occurs when the period of rotation is equal to the period of revolution. An example of synchronous rotation is the Moon, for which the period of rotation and the period of revolution around Earth are both one month. Synodic month The length of time (29.53 days) between successive occurrences of the same phase of the Moon. Synodic period The length of time it takes a Solar System body to return to the same configuration (opposition to opposition, for example) with respect to Earth and the Sun. Tektite A small, glassy material formed by the impact of a large body, usually a meteor or an asteroid. Terminal velocity The speed with which a body falls through the atmosphere of a planet when the force of gravity pulling it downward is balanced by the force of air resistance. Thermosphere The layer of the atmosphere of a planet lying above the mesosphere. The lower thermosphere is the ionosphere. The upper thermosphere is the exosphere. Transverse velocity The part of the orbital speed of a body perpendicular to the Sun between the body and the Sun. Trojan asteroid One of a group of asteroids that orbit the Sun at Jupiter’s distance and lie 60 degrees ahead of or behind Jupiter in its orbit. Troposphere The lowest layer of the atmosphere of a planet, within which convection produces weather. Ultraviolet The part of the electromagnetic spectrum with wavelengths longer than X-rays, but shorter than visible light.

Glossary

257

Umbra The inner portion of the shadow of a body, within which sunlight is completely blocked. V-type asteroid The asteroid Vesta, which is unique in having a reflectance spectra resembling those of basaltic lava flows. Van Allen Belts Two doughnut-shaped regions in Earth’s magnetosphere within which many energetic ions and electrons are trapped. Velocity A physical quantity that gives the speed of a body and the direction in which it is moving. Visual binary star A pair of stars orbiting a common center of mass in which the images of the components can be distinguished using a telescope and which have detectable orbital motion. Wavelength The distance between the crests of a wave. For visible light, wavelength determines color. White hole A hypothetical region of spacetime that cannot be entered from the outside, although matter and light can escape from it. The reverse of a black hole. WIMPS Weakly interacting massive particles, 10 to 100 times the mass of a proton. Wormhole A speculative feature of a black hole that proposedly connects our universe with another universe. X-ray The part of the electromagnetic spectrum with wavelengths longer than gamma rays but shorter than ultraviolet. X-ray burst Sporadic burst of X-rays originating in the rapid consumption of nuclear fuels on the surface of the neutron star in a binary system.

258

Glossary

Zenith The point on the celestial sphere directly above an observer. Zodiacal constellations The band of constellations along the ecliptic. The Sun appears to move through the 12 zodiacal constellations during a year. Zodiacal light The faint glow extending away from the Sun caused by the scattering of sunlight by interplanetary dust particles lying in and near the ecliptic. Zonal winds The pattern of winds in the atmosphere of a planet in which the pattern of wind speeds varies with latitude. Zone of convergence According to plate tectonics, a plate boundary in which the crustal plates of a planet are moving toward one another. Crust is destroyed in zones of convergence. Zone of divergence According to plate tectonics, a plate boundary at which the crustal plates of a planet are moving away from one another. Crust is created in zones of divergence.

Index A Abd al-Rahman al-Sufi, 95, 107, 111 Abu Ishaq Ibrahim al-Zarqali, 90 Abu’l-Fazi ibn Mubarak, 149 Ach Valley tusk fragment, 17–21 Advanced Satellite for Cosmology and Astrophysics (ASCA), 210 Advanced X-ray Astrophysics Facility (AXAF), 213 Agnel, G., 15 Albetenius, 33 Ali Ibn Ridwan, 63 Allan Hills 77005 (ALH 77005), 217 Allan Hills 84001 (ALH 84001), 217, 218 Allen, L. Jr., 197 Allen, T., 69 Al-Mamun, 173 Al-Nayrizi, 33 Andrew Claude de la Cherois Crommelin, 141 Andromeda Galaxy, 77, 78, 109, 117 Antarctic Search for Meteorites (ANSMET), 217 Antoniadi, E.M., 178, 179 Apianus, P., 144, 145, 149 Apollo 8, 185 Apollo 11, 185, 188, 194, 196 Apollo 12, 185 Apollo 13, 197, 207 Arago, D., 115 Aristotle, 74, 87, 123, 141, 142, 146 Armstrong, N., 194 Astrolabe, 29–38 Aubrey, J., 69 Augustus, Tiberius Caesar Divi Augusti filius, 26, 156 Aurora borealis, 12, 223 Australia Telescope Compact Array (ATCA), 70 B Baillie, M, 224 Bayer, J., 43, 111, 112 Bayeux Tapestry, 139, 143 Becvar, A., 119 Beer, W., 187, 188 Bennewitz, P., 144

BeppoSAX, 210 Bergen, University, 11 Bessel, F.W., 150 Bevis, J., 53, 54, 92 Biela’s Comet, 151, 152 Billo, E., 49 Biot, E.C., 47, 139 Blaeu, W.J., 111 Blomboschfontein Nature Reserve, 11 Bonnet-Bidaud, J.-M., 105 Bonomo, A.S., 85 Braasch, O., 167, 168 Brahe, T., 38, 67–69, 71, 90, 110, 112, 118, 123, 126, 127, 145, 146, 148, 161, 175, 176 Brahmagupta, 33 Branch, D., 78 Breuil, H., 10 Brosamer, H., 145 Brown, R.H., 70 Brunovsky, J., 71 Buchwald, V.F., 228 Burnham, S.W., 140 C Cambridge Radio Telescope, 70 Canada-France-Hawaii Telescope (CFHT), 78 Cape Canaveral, 189, 217 Cassini de Thury, C.F., 114, 115 Cassini, G., 114 Cassini, J., 114, 115 Cassiopeia, 65, 67, 69, 147, 180, 182, 213 Cetus, 75 Chacoan, 50–53 Champollion, J.-F., 26, 27 Chandra X-ray Observatory (CXO), 59, 185, 192, 213 Chandrasekhar, S., 40, 78, 213 Charpentier de Charmois, S.F., 114 Chaucer, G., 35 Chelomey, V., 194 Chen Zhou, 107 Cheomseongdae, 169, 170, 173 Chicago, University, 14, 221

© Springer Nature Switzerland AG 2019 J. Powell, From Cave Art to Hubble, Astronomers’ Universe, https://doi.org/10.1007/978-3-030-31688-4

259

260

Index

Chicxulub crater, 230 Chretien, H.J., 200 Christian of Prachatice, 36 Clairaut, A., 53, 54 Claudian, C., 60 Coencas, S., 15 Columbus, C., 89 Comet Churyumov-Gerasimenko, 205 Comet Encke, 118, 150 Comet Hale-Bopp, 225 Comet Halley, 52–54, 92, 137, 139, 141–144, 150, 152–162 Comet McNaught, 152, 153 Comet Shoemaker-Levy 9, 205, 225 Compton Gamma Ray Observatory (CGRO), 185, 186, 192, 211 Comte de Cassini, J.-D., 115 Conrad, C.P. Jr., 185 Contarini, G., 74 Contractus, H., 34 Coombs, A., 14–16 Copernicus, N., 68, 74, 95, 127 Cornelis de Houtman, 111 Corsali, A., 109 Cosmos, 3, 4, 21, 29, 87, 102, 127, 196, 197, 201, 202 COSTAR (Corrective Optics Space Telescope Axial Replacement), 198, 201 Cowell, P.H., 139, 141 Crab Nebula, Pulsar, 42, 43, 46, 47, 49, 52–58, 66, 92, 116, 139 Crabtree, W., 121–123, 125, 126, 128–131, 133 Cro-Magnon, 12, 18 Curtis, H.D., 55, 56 Curtz, A., 148 Cuvier, G., 27 D Dalmasso, M., 85 Dee, J., 68 Delisle, J.-N., 114 Dendera Zodiac, 24–27 Descartes, R., 123, 124 Digges, L., 68 Digges, T., 68 Dominion Radio Astrophysical Observatory, 66 Douglass, A.E., 220, 221 Dresden Codex, 89 Dreyer, J.L.E., 118, 119 Ducretet, E.A., 179 Duncan, J.C., 56

Dunhuang map, 103, 104, 107 Dunsink Observatory, 139 Durham, University, 65 E Earth, 1, 13, 25, 30, 41, 81, 96, 121, 140, 163, 215 Edinburgh, University, 13 Einstein, A., 6, 82, 191 Elizabeth I, 69, 124 Ellis, R.S., 78 Encke, J.F., 149, 150 Eratosthenes, 100, 101 European early modern humans (EEMH), 18 European Space Agency’s (ESA), 54, 59, 116, 186, 190, 196, 205, 206, 212 European Space Research Organization (ESRO), 196 European X-Ray Observatory (EXOSAT), 210 Explorer 11, 211 F Fabricius, D., 75, 76 Fabricius, J., 76 Farnese, A., 28 Farnese Atlas, 27, 28 Fermi Gamma-ray Space Telescope (FGST), 212 Fesen, R.A., 57, 66, 78 Firuz Shah Tughluq, 36 Flamsteed, J., 43, 53, 117, 118, 132, 162, 180 Foster, S., 129 Fourier, J.-B.J., 27 Fresnal, A.-J., 115 Fujiwara Sadaie, 47 G Gagarin, Y., 195 Gaia spacecraft, 116, 205, 206 Galilei, G., 7, 74, 91, 109, 122, 150 Gaocheng Astronomical Observatory, 173–174 Gardener, F.F., 61 Gascoigne, W., 125, 126, 131 Gassendi, P., 91, 123, 124, 126, 128, 130, 132 Gemini 11, 185 Gemma, C., 148 German Aerospace Center, 60, 230 Giacconi, R., 208, 209 Gilbert, W., 123, 124 Giulio Cesare della Scala, 74 Glenn, J.H. Jr., 30 Gobekli Tepe, 14, 15 Gordon, R.F. Jr., 185

Index Goseck circle, 98, 167, 168 GRACE (Gravity Recovery and Climate Experiment) satellite, 230 Great Comet’s 1577, 72, 145–148 Great Comet’s 1744, 113 Gully, L., 77 Guo Shoujing, 174 Gursky, H., 209 H Hajek, T., 69 Hale, G.E., 200 Hale telescope, 200 Halley, E., 53, 116, 137, 149, 154, 156, 157, 161, 162 Halley's Comet, 52–54, 92, 137, 139, 141–144, 150, 152–162, 225 HARPS-N spectrograph, see Telescopio Nazionale Galileo Harriot, T., 150 Hartwig, C.E.A., 77 Harvard-Smithsonian Center for Astrophysics, 85 Hawking, S., 6, 214 Hawkins, G.S., 165 Hazard, C., 70 Henshilwood, C., 11 Herschel, C.L., 116, 117 Herschel, J.F.W., 118 Herschel Space Observatory (HSO), 54, 205 Herschel, W., 54, 117, 180, 188 Hevelius, J., 38, 118, 132, 146 High Energy Astronomy Observatory (HEAO-1), 210 Hind, J.R., 139–141 Hipparchus, 13, 28, 75, 95, 96, 103, 165 Hipparcos (High Precision Parallax Collecting Satellite), 205 Holt, H.E., 34 Honda, M., 192 Hondius, J., 111 Hooke, R., 126, 132, 177 Hooker telescope, 55, 56 Ho Peng Yoke, 45, 46 Horrocks, J., 121–123, 125, 126, 128–133 Hubble, E., 57, 185, 186, 192, 196–199, 201–205 Hubble Space Telescope (HST), 54, 57, 78, 140, 164, 184–186, 188, 189, 192, 196–205 Huygens, Christiaan, 133 Huygens, Jr. Constantijn, 133

261

I Ibn Abi Usaybi, 48 Ibn al-Saffar, see Mashallah ibn Athari Ibn Bajjah, 90 Ibn Butlan, 48 Ibn Sina, 61–63 Indian Space Research Organisation (ISRO), 206 Infrared Space Observatory (ISO), 190 Innes, R.T.A., 152, 153 Instituto Nazionale Di Astofisca (INAF), 85 International Astronomical Union (IAU), 83 International Dark-Sky Association (IDA), 163 International Gamma-Ray Astrophysics Laboratory (INTERGRAL), 212 International Space Station (ISS), 184 Interstellar Medium (ISM), 41 Istanbul, University, 14 J Japan Aerospace Exploration Agency (JAXA), 205 Japanese National Institute of Polar Research, 217 Jet Propulsion Laboratory (JPL), 139, 197 Jodrell Bank Observatory, 70 Johannes van Heeck, 73 Joy, A.H., 140 Jupiter, Io, Europa, Ganymede, Callisto, 109, 110, 177 K Kaempffert, W., 179 Kamen, M.D., 222 Keck telescope, 78, 199 Keeler, J.E., 55 Kennedy Space Center, 184, 185 Kepler, J., 36, 67, 72, 73, 75, 76, 90, 91, 110, 123–126, 128, 132, 146, 147, 161, 176 Kessler, D.J., 185 Keyser, P.D., 111 Kitt Peak Observatory, 78 Kjaer, K., 227 Klepesta, J., 119 Klinkenberg, D., 113 Koch, L., 228 Kokino, 168, 169 Komarov, V., 194, 207 Korff, S.A., 221 Korolev, S., 194

262

Index

Kothes, R.J., 65, 66 Krupp, E.C., 49, 50 Kurie, F.N.D., 222 L Lampland, C.O., 55, 56 Lansberg, P., 123, 128 Laplace, P.-S., 6 Large Magellanic Cloud (LMC), 67, 108, 109 Lascaux caves, 10, 15, 16 Laser Interferometer Space Antenna (LISA), 205, 212 Lefrancois de Lalande, J.J., 118 Leonov, A., 195 Lepaute, N.-R., 53, 54 Libby, W.F., 221 Li Chunfeng, 107 Lick Observatory, 55–57 Ligorio, P., 145 Li Tao, 45 Li Zeng, 85 Local Interstellar Cloud (LIC), 41 Lodovico delle Colombe, 73 Lowell Observatory, 54, 55, 190, 220 Lowell, P., 56, 220 Loys de Cheseaux, J.-P., 113 Lundmark, K., 56, 57 Lupus, 61, 63 M Madler, J.H., 187, 188 Ma Duanlin, 47 Maestlin, M., 148, 149 Mahendra Suri, 36 Mair, A., 112 Maraldi, G.D., 114 Maraldi, G.F., 114, 115 Maraldi, J.-D., 115, 116 Mare Crisium, 100 Mare Imbrium, 195 Marius, S., 109, 110 Mark, R., 49 Mars, 55, 63, 72, 76, 84, 86, 87, 114, 149, 172, 177–179, 188, 206, 207, 216–218, 220 Marsal, J., 15 Martyr d’Anghiera, P., 109 Marzi Medici, A., 73 Mashallah ibn Athari, 35 Matilda of Flanders, 144 Maurolico, F., 69 Maury, M.F., 151

Mayall, N.U., 57 Mayall Telescope, see Kitt Peak Observatoary Mayer, C., 132 Mechain, P., 149 Mencius, 106 Mercator, G., 124 Mercury, transit, Caloris Basin, 83 Messier, C., 53, 54, 93–120, 149, 150 Messier 1 (M1), 116 Messier 2 (M2), 115, 116 Messier 15 (M15), 115 Messier 31 (M31), 116 Messier 87 (M87), 5, 55 Messier 110 (M110), 116, 117 Michell, J., 6, 7 Microwave Anisotropy Probe (MAP), 212 Milky Way, 5, 41, 56–57, 71, 76, 109, 112, 116, 180, 181, 196, 206, 211, 213 Miller, W.C., 49, 50, 52 Milne, D.K., 61 Montaigne, J.L., 150 Moon, crescent, 21, 23, 49, 50, 52 Moore, P., 187 Mount Wilson Observatory, 56 Muhammad, 35 Muhammad al-Fazari, 33 Muhammad ibn Abi Bakr al Ibari, 34 Mullard Radio Astronomy Observatory (MRAO), 70 Munckley, N., 92 N Nagoya University, 220, 223 National Aeronautics and Space Administration (NASA), 5, 12, 23, 30, 59, 72, 91, 108, 122, 184–187, 191, 192, 196–198, 205, 206, 211, 212, 217, 218, 228, 230 Nebra Sky Disc, 21–24 Needham, J., 105 Neil Gehrels Swift Observatory, 212 Neptune, 55, 82, 84 Neuhauser, R., 61–63 Newton, I., 82, 115, 122, 132, 150, 161 O Oberth, H., 186 Occhialini, Guiseppe Paolo Stanislao Beppo, 210 Odo of Bayeux, 143 Office of Polar Programs of the National Science Foundation (NSF), 217 Ohio State University, 230

Index Oklahoma, University, 78 One-Mile Radio Telescope, see Mullard Radio Astronomy Observatory (MRAO) Ophiuchus, 71, 75, 76 Optical Gravitational Lensing Experiment (OGLE), 191 Orbiting Astronomical Observatory 2 (OAO-2), 186, 192, 193 Orbiting Solar Observatory (OSO), 210 Orion 1, 193 Orion 2, 193 Ostendorfer, M., 145 Otto Wilhelm von Struve, 140, 151 P Palitzsch, J.G., 162 Palomar Mountain Telescope, 70 Palomar Observatory, 34, 49, 190 Paolini, F., 208 Parker Pearson, M., 165 Parkes Observatory, 61, 182 Parsons, W., 55 Pelliot, P.E., 105 Peregrinus, P., 35 Pescheck, C., 162 Philoponus, J., 32 Photoconductor Array Camera and Spectrometer (PACS), 54 Piccolomini, A., 112 Pic du Midi Observatory, 179 Pieter van der Keere, 111 Pigafetta, A., 109 Plancius, P., 111 Plato, 87 Plato Tiburtinus, 33 Pleiades, 155 Pluto, 55, 56, 204, 220 Poisson, S.-D., 114, 115 Pons, J.-L., 149, 150 Potts, L., 230 Prince Henry, 36 Ptolemy, C., 31, 87, 95, 107, 111, 123 Pulkova Observatory, 141 Q Qotb al-Din Shirazi, 90 R Ralph von Frese, 230 Ranger 4, 195 Rappengluck, M.A., 19–21

263

Ravidat, M., 15, 16 RCW 86, 58, 59 Reber, G., 181, 182 Reisacher, B., 69 Renzong, E., 44 Ritchey, G.W., 56, 200 Robotic Optical Transient Search Experiment (ROTSE-I), 212 Rogers, J.H., 27 Rontgen, W., 210 ROSAT, 60, 70, 210 Roselin, H., 72–74 Rosetta spacecraft, 205 Rosetta stone, 26, 27 Rossi, B.B., 208 Rossie X-ray Timing Explorer (RXTE), 210 Royal Greenwich Observatory, 176, 179–180 Ruben, S., 222 Rudolf II, Holy Roman Emperor, 126 Rudolphine tables, 125–128 Russell, T., 68 Ryle Radio Telescope, see Mullard Radio Astronomy Observatory (MRAO) S Sagittarius A∗ (Sgr A∗), 5, 213 Salyut 1, 193, 207 Salyut 2, 196 Salyut 3, 196 Salyut 5, 196 Sanduleak, N., 67 Saturn, 54, 72, 81, 84, 86, 87, 115, 130, 172, 177, 189 Schmidt, J.F.J., 187, 188 Schmidt, K., 14 Schroter, J.H., 187 Schuler, W., 67, 68 Schwarz, R., 168 Scorpio, 25, 76 Sebokht, S., 32 Seneca, 136, 141 Seven Sisters, see Pleaides Shakerley, J., 131 Shakespeare, W., 68 Shapley-Curtis debate, 56 Shapley, H., 56 Sharaf al-Din al-Tusi, 34 Shereburn, E., 131 Shi Shen, 93–120 Sidney van den Bergh, 66 Slipher, E.C., 54 Slipher, V.M., 54 Small Magellanic Cloud (SMC), 108, 109

264

Index

Smithsonian Astrophysical Observatory, 193 Solar and Heliospheric Observatory (SOHO), 205 Somayaji, N., 90 Soyuz 11, 207 Soyuz 13, 193 Space Infrared Telescope Facility (SIRTF), see Spitzer Space Telescope (SST) Space shuttle Challenger, 207 Columbia, 198, 207 STS-37, 211 STS-61, 197, 198 STS-82, 198 STS-103, 198 STS-109, 198 STS-125, 198 Spitzer, L.S. Jr., 211 Spitzer Space Telescope (SST), 23, 59, 108, 185, 189–192, 199, 210, 211 Sputnik 1, 188 State Museum of Prehistory, Halle, Germany, 24 Stein, M.A., 104, 105 Stephenson, R., 65 St. Leger, Anne, 68 Stonehenge, 14, 164–166, 168, 169 Supernova (SN) SN 393, 60 SN 1006, 47, 60–62, 64, 65, 171, 231 SN 1054, 39, 41–49, 52, 56–58, 61, 63, 64, 66, 73, 139, 171, 231 SN 1181, 47, 65, 66 SN 1572, 67–71, 73, 147, 148, 171 SN 1604, 67, 71–73, 75, 147, 171 SN 1885A, 77 SN 2003fg, 78 Supernova/supernovae, 17, 39–79, 94, 138, 139, 147, 148, 171, 180, 209, 213, 215, 216, 223, 231 Sweatman, M., 13–16 T Tao Kiang, 139 Taqi al-Din Muhammad ibn Ma’ruf ash-Shami, 145 Telescopio Nazionale Galileo, 85 Theon of Alexandria, 32 Thiele, G., 28 Thoedosius, M.A., 99 Thomas, N.G., 34 Tirion, W., 119 Titan Atlas, 27 Titus Flavius Josephus, 156

Tombaugh, C., 55 Toru Yamada, 57 Towneley, C., 126 Towneley, R., 126 Transvaal Observatory, 152 U UNESCO (United Nations Educational, Scientific, and Cultural Organization), 24, 65, 141, 164 Unetice culture, 22 Uraniborg Observatory, 174–176 Uranographia Britannica, 53, 92 Uranus, 82, 84, 180 Urbain Le Verrier, 82 US Naval Observatory, 114, 179, 200 V Venus, transit, 54, 90, 92, 121–133 Very Large Telescope, 200 Voskhod 2, 195 Vostok 1, 195 Vulture Stone, 15 W Wainwright, G.J., 165 Wallis, J., 132 Wang Ling, 105 Wang YuanIu, 104 Wang Yun, 174 Wanli, Emperor, 69 Ward, I., 76, 77 Weihaupt, J.G. Jack, 229 Westerbork Synthesis Radio Telescope (WSRT), 70 Wide-field Infrared Survey Explorer (WISE), 59 Widemann, K., 148 Wilhelm von Biela, 150 Wilkinson Microwave Anistropy Probe (WMAP), 212 Williams, B.J., 59 Wright, E., 123–125 Wurdi Youang, 166 Wu Xian, 106 X XMM-Newton Observatory, 59 X-ray Explorer Satellite, 209 Xunzi, 106

Index Y Yaqub ibn Tariq, 33 Yeomans, D., 139 Yerkes Observatory, 56, 200 Yongle Emperor, 44 Younger Dryas event, 15, 227, 228 Young, T., 27

Z Zhang Juzheng, 69 Zhou Keming, 64 Zhu Zaiji, 69 Zupi, G.B., 91 Zwicky, F., 41

265