Early Greek Astronomy to Aristotle

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Early Greek Astronomy to Aristotle

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EARLY GREEK ASTRONOMY to Aristotle

ASPECTS OF GREEK AND ROMAN LIFE General Editor: Professor H. H. Scullard

EARLY GREEK ASTRONOMY to Aristotle D. R. Dicks

CORNELL UNIVERSITY PRESS ITHACA, NEW YORK

© 1970 D. R. Dicks All rights reserved. Except for brief quotations in a review, this book, or parts thereof, must not be reproduced in any form with¬ out permission in writing from the publisher. For information address Cornell University Press, 124 Roberts Place, Ithaca, New York 14850.

Standard Book Number 8014-0561-0 Library of Congress Catalog Card Number 76-109335 PRINTED IN ENGLAND

CONTENTS PREFACE

III

6

I

GENERAL PRINCIPLES

9

II

HOMER AND HESIOD

27

THE PRE-SOCRATICS TO ANAXAGORAS

39

IV THE PYTHAGOREANS AND LATER PRE-SOCRATICS

V

VI

VII

PLATO

92

EUDOXUS

151

CALLIPPUS AND ARISTOTLE

ABBREVIATIONS

NOTES

221

INDEX

268

219

190

PREFACE The achievements

of the Greeks in the field of astronomy must

rank among the most enduring which even that gifted race has bequeathed to posterity. Every time we make use of a celestial globe, a planisphere, a star map, or a planetarium, we use con¬ cepts for which we are indebted to the ancient Greek astronomers; for it was they (and they alone of the peoples of antiquity) who conceived and developed the essential, theoretical basis of all such astronomical tools, i.e. the celestial sphere as a mathematical extension in space of the terrestrial sphere, with the observer envisaged as being at the centre of the cosmos. Yet only one book dealing exclusively with ancient Greek astronomy has appeared in English since T. L. Heath’s Aristarchus of Samos (Oxford, 1913), namely, the same scholar’s much slighter Greek Astronomy (Dent, London, 1932), a selection of translations preceded by a ‘potted’ history of astronomy, mostly adapted from his larger work but with a few additional pages to bring the storydown to Ptolemy (who receives eight lines!) and some unreliable material on Egyptian and Babylonian astronomy (not touched on in the earlier work). Heath’s Aristarchus has held the field for over fifty years, just as his admirable History of Greek Mathematics (2 vols., Oxford, 1921) has become a classic in that sphere. Meanwhile, our knowledge of the history of science (particularly early science) has increased considerably. We know much more about Egyptian and Babylonian astronomical methods. We can assess to some extent how much the Greeks were influenced by or borrowed from these sources (although when and how such interaction took place are very debatable questions - see pp. 165^), and we are perhaps less inclined to accept uncritically the accounts of the doxographers and commentators of later antiquity who attribute comparatively advanced astronomical concepts to the early Greek 6

PREFACE

7

thinkers in defiance of all probability. Also our understanding of Plato’s astronomical ideas has been substantially enlarged by F. M. Cornford’s brilhant work on the Timaeus (Plato’s Cosmology, London, 1937). The present volume attempts to take into account at least some of the work done since the publication of Heath’s Aristarchus. I have been concerned to trace the development of astronomy as a science, rather than that of cosmology or cosmogony, and so the cosmological fantasies of the Pre-Socratics receive shorter shrift than some scholars may think such theories merit. I make no apology for this; elsewhere I have pointed out the fallacies attendant on an overestimation of the scientific content of PreSocratic thought (CQ 9, 1959, pp. 294-309; JHS 86, 1966, pp. 26-40), and the chief criticism that may be directed against the earlier part of Heath’s book is that he tends to treat as of equal value all the evidence that has come down to us via the scrapbooks and compilers of later times concerning the astronomical ideas of the Pre-Socratics, and, without considering the implications, to accept accounts as trustworthy that are only implausible guesses, contradictory in themselves and anachronistic in the context. Some justification is perhaps needed for the fact that this volume ends with Aristotle, thus covering a shorter span than Heath, who naturally took Aristarchus (some two generations after Aristotle) as his terminal point. The main reason is that Plato (whose import¬ ance in the development of Greek astronomy is commonly under¬ estimated) and Eudoxus are treated here at greater length (Chapters V and VI), and more attention is paid to such topics as the origin of the constellations (pp. 159$) and the influence of Babylonian astronomy on that of the Greeks (pp. 16^ff.). Aristotle makes a particularly appropriate point at which to divide a history of Greek astronomy, since after him mathematical astronomy under¬ goes a relatively rapid development along lines that not only contrast strongly with pre-Aristotelian speculative thought, but also are substantially different from those laid down by Eudoxus in Aristotle’s own lifetime. It is, too, in the early history of astro¬ nomy, where the reliable evidence is scanty and its interpretation uncertain, that the greatest number of erroneous notions and inept

8

PREFACE

judgments is commonly found; commentators (both ancient and modern) have been all too prone to read into early scientific thought ideas which are only appropriate to a later stage of development. It is hoped to follow the present volume with another dealing with later Greek astronomy, which will include some discussion of the influence of astrological doctrines on astronomical thought; traces of such doctrines can be found in Greek writings dating from the end of the fifth century

bc,

but

astrology does not become influential in Greek thought until Hellenistic times (see my Geographical Fragments of Hipparchus, London, i960, pp. 12ff.\ cf. Hermes 91, 1963, pp. 6off.), and so belongs properly to the second volume. I am grateful to Professor H. H. Scullard, the General Editor of this series, for first suggesting that I should contribute an account of Greek astronomy, and to him and the pubhshers for agreeing that it should be in two volumes. Its preparation has been greatly facihtated by a year’s leave of absence, generously granted by the authorities of Bedford College, to take up a Visiting Professorship at Princeton University for the first semester in 1966 and to work at the Institute for Advanced Study, Princeton, during the second semester. I acknowledge with deep gratitude the many kindnesses of Professor Marshall Claggett of the above Institute and of Professor Charles Gilhspie of the Program in History and Philosophy of Science, Princeton University, who between them, made all the necessary arrangements for my most enjoyable stay. I should also like to record my great appreciation of the work done by the members of the graduate seminar on Greek Astronomy which I was privileged to give; I learnt much from them, and was greatly impressed by their enthusiastic interest in and application to a somewhat esoteric subject - especially since not a single one of them was a classics graduate. Finally, although it may be invidious to single out one name when all the members of the above Program (and indeed of the whole Department of History) did so much so willingly to help me in different ways, I wish to tender my special thanks to Dr Michael Mahoney for his readiness to give unstintingly of his time and knowledge in both profes¬ sional discussion and extra-curricular activities.

CHAPTER I

GENERAL PRINCIPLES1 All

ancient

astronomy

was based entirely on naked-eye

observation (as, indeed, was all astronomy up to the end of the sixteenth century). This simple fact is often overlooked. Modern commentators tend to underestimate the difficulties of such observation and to discuss the results as though the telescope, the micrometer screw, and the vernier scale were normal pieces of equipment in antiquity. In reality, of course, none of these aids existed and without them it is by no means easy to make measure¬ ments of even a low standard of accuracy with the naked eye alone; intelligent application, assiduous practice in estimating changes of position in the night sky, and above all an excellent memory combined with access to similar observations recorded over as long a period as possible, are the minimum requirements to produce any meaningful results. To distinguish, for example, between a planet and a fixed star (easy enough with the lowestpowered binocular or telescope) is not at all a simple matter when one gazes on the myriad points of fight in the heavens, especially when the atmosphere is clear (as might be expected in ancient Greece) and the phenomenon of‘twinkling’ is less in evidence; to differentiate between the planets themselves, and estimate their periods, must have taken centuries of observation. We shall see later that the results obtained by even such a competent observer as Eudoxus (whose ‘observatory’ - probably nothing more than a flat-topped building - was still pointed out in the time of Strabo; see pp. 151f) were far from accurate, and were reflected in the inadequacy of his solar theory in particular. There is practically no evidence as to what instruments were used to make astronomical observations before the third century

bc.2

It is a fair inference that

measurements of the shadow cast by the gnomon, i.e. any vertical 9

10

EARLY GREEK ASTRONOMY TO ARISTOTLE

pointer on a horizontal base - probably introduced from Babylonia (see pp. i6$f) in the fifth century - were used to determine the solstices and the time of midday (see below), and it is hkely that a simple rotating globe with the chief circles of the celestial sphere and some of the better-known constellations marked on it formed part of an astronomer’s equipment from at least the time of Eudoxus onwards; but what sighting instrument was used (if any) is wholly unknown. It is not improbable that angular distances were estimated simply by means of the hand stretched out at arm’s length in front of the eye; a possible reminiscence of such a usage may be found in the use of the word 8