Early Astronomy

276 Pages·1994·14.61 MB·English

by  Hugh Thurston (auth.)

Early Astronomy
Springer
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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
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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
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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.