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Early Astronomy PDF

276 Pages·1994·14.61 MB·English
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Early Astronomy Springer New York Berlin Heidelberg Barcelona Budapest Hong Kong London Milan Paris Santa Clara Singapore Tokyo Hugh Thurston Early Astronomy With 139 Illustrations Springer Hugh Thurston University of British Columbia Department of Mathematics 121-19114 Mathematics Road Vancouver, BC Canada V6T 1Y 4 All photographs first appeared in The Griffith Observer (used by permission) Cover illustrations: Tycho's great sextant (Figure 10.6) and the Systema Tychonicum (from The Scientific Image) Library of Congress Cataloging-in-Publication Data Thurston, Hugh, 1922- Early astronomy/Hugh Thurston,-Ist ed. p. em. Includes bibliographical references and index. ISBN-13: 978-0-387-94822-5 e-ISBN-13: 978-1-4612-4322-9 DOl: 10.1007/978-1-4612-4322-9 1. Astronomy. Ancient. 1. Title. QB16.T48 1993 520'.93-dc20 93-5142 Printed on acid-free paper. First softcover printing, 1996. © 1994 Springer-Verlag New York, Inc. All rights reserved. This work may not he translated or copied in whole or in part without the written permission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York. NY 10010. USA), except for hrief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or hy similar or dissimilar methodology now known or hereafter devcloped is forhidden. The use of general descriptive names, trade names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used fredy by anyone. Production coordinated by Brian Howe and managed by Bill Imbornoni; manufacturing supervised hy Genieve Shaw. Typeset by Best-set Typesetter Ltd., IIong Kong. 987654321 Contents Introduction IX 1. Early Stargazers 1 The Celestial Bowl 1 The Constellations 2 The Rotation of the Heavens 4 Small Irregularities 7 The Sun 8 The Directions of Sunrise and Sunset 9 The Irregular Sun 11 The Moon 12 The Directions of Moonrise 13 The Cycles of the Moon 15 The Irregular Moon 17 Eclipses 17 The Luni -Solar Calendar 19 The Planets 20 Venus Observed 21 Rising Azimuths 23 Thc Stars 24 Heliacal Risings 24 Precession 24 Precession and the Pyramids 25 The Astronomer's Tools 26 Celestial Latitude and Longitude 32 Armillaries 35 Polar Elevations and the Obliquity of the Ecliptic 41 2, Megalithic Astronomy 45 Stonehenge 45 Other Megalithic Structures 55 3. The Babylonians 64 Early Period 64 v VI Contents The Mul-Apin Tablets 64 The Zodiac 66 Observations 68 Sexagesimal Numerals 69 Late Period 71 The Sun 71 The Moon 74 Latitude 74 The Lengths of the Months 75 System B 78 Lengths of Fundamental Periods for the Moon 78 The Planets 79 4. The Egyptians R2 5. The Chinese R4 Introduction 84 Chinese Units 86 Units of Length 137 Dates 137 Time of Day 90 Cosmology 90 Almanacs 91 The Length of the Year 92 Official Records 93 Noon Shadows 96 A Tang Dynasty Survey 96 The Exact Instant of the Solstice 97 Later Developments 101 Thc Length of the Year 105 Thc Obliquity of the Ecliptic 105 Celestial Motions 106 The End of the Story 109 6. The Greeks 110 The Early Thinkers 110 The Classical Greeks 111 Meton and Euctcmon 111 The Greek Zodiac 112 Eudoxus li2 Aristotle 117 The Size of the Earth 1113 Does the Earth Move') 121 Aristarchus 122 Hipparchus 123 The Length of the Year 125 Periods of the Moon 127 Table of Chords 1213 Contents vii The Sun's Motion 128 The Moon's Motion 131 Precession 135 A Possible Origin for the Constellations 135 Ptolemy 138 The Sun 140 The Moon 143 The Distance of the Moon 147 The Distance of the Sun 149 Eclipses 149 The Stars 150 The Planets 155 Mercury 159 Venus 163 Mars 166 Accuracy 169 Calculations from the Theory 170 Latitudes 170 Note on the Epicycle Theory 170 Closing Remarks on the Almagest 171 The Ptolemaic Univcrse 171 7. The Astronomy of Aryabhata ms The Sun 180 The Moon 181 The Planets 181 Further Topics 187 Unwritten Astronomy 188 8. Arabic Astronomy 190 9. The Mayas 196 The Moon 198 Vcnus 199 Eclipsc Table 201 The Accuracy of the Maya Calendar 202 10. The European Renaissance 205 Copernicus 205 Tycho Brahc 210 Kepler 217 The Latitude of Mars 220 The First Theory of Mars 222 The Earth 225 Mars Again: Is its Orbit a Circle? 227 The Orbit of Mars Is an Ellipse 230 Kepler's Laws 232 VIII Contents Appendix 1. Hipparchus's Table of Chords 235 Appendix 2. Calculation of the Eccentric-Quotient for the Sun, and the Longitude of its Apogee 237 Appendix 3. Ptolemy's Table of Chords 239 Appendix 4. Calculating the Radius of the Moon's Epicycle 240 Appendix 5. The Eccentric-Quotient and Apogee of Mars 244 Appendix 6. Reversed Epicycles 246 Further Reading 249 Sources of Information 252 Index 259 Introduction People must have watched the skies from time immemorial. Human beings have always shown intellectual curiosity in abundance, and before the invention of modern distractions people had more time-and more mental energy-to devote to stargazing than we have. Megaliths, Chinese oracle bones, Babylonian clay tablets, and Mayan glyphs all yield evi dence of early peoples' interest in the skies. To understand early astronomy we need to be familiar with various phenomena that could-and still can-be seen in the sky. For instance, it seems that some early people were interested in the points on the horizon where the moon rises or sets and marked the directions of these points with megaliths. These directions go through a complicated cycle-much more complicated than the cycle of the phases of the moon from new to full and back to new, and more complicated than the cycle of the rising and setting directions of the sun. Other peoples were interested in the irregular motions of the planets and in the way in which the times of rising of the various stars varied through the year, so we need to know about these phenomena, i.e., about retrogression and about heliacal rising, to usc the technical terms. The book opens with an explanation of these matters. Early astronomers did more than just gaze in awe at the heavenly bodies; they tried to understand the complex details of their movements. By 300 H.C. the Babylonians had devised an intricate arithmetical system for this purpose, and by A.D. 150 the Greeks had developed a powerful geometrical theory that was capable of representing the motions of the sun and planets remarkably accurately. Another great early civilization, Egypt, had disappointingly little astronomy, but China's contribution was substantial and interestingly different from that in the west. It reached its peak in the late thirteenth century, to be superseded soon after by western astronomy introduced by Jesuit missionaries. China's astronomy had a nudge from Babylon in early historical times, and classical Indian astronomy almost certainly developed from early Greek geometrical theories, but the Mayas, far IX x Introduction away in central America, developed an astronomy entirely independent of the astronomy of the Old World. These astronomies all had the sun moving round the earth. They were superseded eventually by Copernican astronomy, in which the earth moves round the sun. Copernicus led to Kepler, the first person to find the true shape of the planets' orbits. And then-some forty centuries after the megaliths came a natural watershed. Up to this date, astronomy had been a matter of patient observation with simple instruments, little more than jointed rods and pivoted rings, followed by pencil-and-paper calculations. But Galileo, a contemporary of Kepler. altered all this. First, he used the newly-invented telescope to look at the moon and the planets. This revolutionized astronomical observation, leading eventually to today's sophisticated observatories with their computer-controlled telescopes. Second, he began to develop a theory of motion. In the hands of Isaac Newton such a theory would eventually explain the celestial motions in terms of well-founded physical principles. Astronomy became part of physics. This book covers astronomy from the beginning up to the time of Kepler. Most of this was developed at a time when other sciences. notably physics and chemistry, had scarcely started. The scientific edifice built up over this period is one of the triumphs of human intellect. I would like to acknowledge the willing and friendly help of Mr. S. Y. Tse, of the Asian Centre Library, University of British Columbia, of Professor Ashok Aklujkar, of the Department of Asian Studies, Uni versity of British Columbia, and of Dr. Edwin C. Krupp, of the Griffith Observatory. Los Angeles.

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