Table Of ContentUnderstanding the Heavens
Springer-Verlag Berlin Heidelberg GmbH
ONLINE LlBRARY
Physics and Astronomy
http://www.springer.de/phys/
Jean-Claude Pecker
Understanding
the Heavens
Thirty Centuries of Astronomical Ideas
from Ancient Thinking
to Modern Cosmology
Edited by Susan Kaufman
With 256 Figures
Including Many Historical and Hand-Drawn Illustrations
, Springer
Professor Jean-Claude Pecker
College de France
AnnexeUlm
3rue d'Ulm
75231 Paris Cedex 05
France
Caver picture: Stonehenge from the air. The axis of the monuments is roughly aligned with the Heel
Stone, seen on the lower left edge of the picture. The Aubrey Holes, which a modern astronomer
could use for eclipse prediction, are seen in the outer ring ofwhite dots. (Cambridge University
Collection of Air Photographs: copyright reserved)
Library of Congress Cataloging-in-Publication Data
Pecker, Jean Claude.
Understanding the heavens : thirty centuries of astronomieal ideas from aneient
thinking to modem eosmology / Jean-Claude Peeker ; edited by Susan Kaufman.
p.em.
Includes bibliographieal referenees and index.
ISBN 978-3-642-08325-9 ISBN 978-3-662-04441-4 (eBook)
DOI 10.1007/978-3-662-04441-4
1. Astronomy--Hisiory. I. Title.
QBI5 .P38 2001
520' .9--de21
00-024396
ISBN 978-3-642-08325-9
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Foreword
This book sterns from aseries of lectures given to a select group of un
dergraduate students at Williams College in Williamstown, Massachu
setts where I taught at the kind invitation of Professor Jay Pasachoff in
the fall of 1989. I want to heartily thank Jay Pasachoff for this wonderful
opportunity to resurne the activity of teaching the young, a very stimu
lating one indeed; and I want to thank the students themselves for the
many exciting debates I had with them about the questions treated in
this book and other interesting subjects.
The book covers almost three millennia of the evolution of ideas
ab out what is now called the "Universe" but which, until the 18th cen
tury, was called the "World:' It is not always an easy book. It is intended
for the learned student, whatever his level, undergraduate or graduate, in
astrophysics or in history or related fields. The more difficult passages
are either grouped in appendices or indicated by an asterisk (*).
I must insist that I am by no means an historian, onlyan astrophysi
eist trying to reveal the concepts and predispositions that may be lying
behind some of the model universes published in the literature. To ad
vance an understanding of these models, I have, therefore, gone into spe
eific descriptions, sometimes involving mathematical details, with the
conviction that this thorough understanding is necessary to follow the
evolution of ideas.
I would like to express my thanks to Springer-Verlag and in particular
to Professor Wolf Beiglböck, who agreed to publish this book even be
fore it was in a readable form and whose staff helped so much in all the
phases of its completion. I want to additionally express my thanks to all
of my colleagues and friends who have provided documentation or illus
trations, in particular Dr Laurent Nottale, who carefully read the last
three chapters. I deeply appreeiate the friendly hand given by my two
co-writers, Dr Daniel Pecker, for the appendix in Chap. 5, and Dr Simone
VI Foreword
Dumont, for Chap.6, who have both devoted much of their time to
developing these two parts of the book from rough text to final version. I
am grateful to Dr Suzanne Debarbat who helped with some of the tables
and the chronology and to the Chief Librarians of both the Observatoire
de Paris and the Institut de France, and their assistants, Mme Pastoureau
and Mme Chassagne at the Institut, and Mme Dalies and Mlle Alexandre
at the Observatoire whose help was invaluable in finding the needed an
cient documents.
English is not my mother tongue. Ms Susan Kaufman in Massachu
setts was tremendously helpful in transforming my "Frenglish" into per
feet English. We had many exchanges, mostly by fax, over the ocean
from Great Barrington to the Ile d'Yeu and vice versa and I must say it
was a pleasant and fruitful experience. To Ms Dominique Bidois who
converted the text from the original Claris to Word, I also owe many
thanks.
At long last, the book is in print with the best possible help from the
staff at Springer Verlag. Ms Andrea Kübler and Ms Friedhilde Meyer
dealt primarily with the text itself. Ms Brigitte Reichel-Mayer took·great
care in gathering old documents. Despite my unusual requirements, they
kept their good humor and I am grateful to them for their excellent
work. Of course, this book is also the product of the efforts of many peo
pIe behind the scene whose names are unknown to me. Last, but not
least, I am grateful to my wife, not only for her material help in the edit
ing process, but still more for her patience and understanding love dur
ing the several years of preparation of this book.
This book's appearance coincides with the beginning of a new cen~
tury. Let us hope that it stimulates more research on the state and evolu
tion of our knowledge and understanding of the heavens.
L'ile d'Yeu Jean-Claude Pecker
May 10th, 2000
Contents
Introduction and Perspectives ..................................... 1
The Theory of Scientific Revolutions ............................... 2
Interactions Between Politics and Scientific Progress ............... 5
The Continuous Progress of Astronomical Techniques. . . . . . . . . . . . . . 8
The Three Streams from Pythagoras, Plato, and Aristotle........... 10
1. Before the Classical Greek Period.............................. 15
1.1 A General Overview of a Rapid Evolution. . . . . . . . . . . . . . . . . . . . . . 15
1.2 Elementary Naked-Eye Astronomy............................. 21
1.2.1 The Two Luminaries ..................................... 21
1.2.2 The Solar Cydes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.2.3 The Moon's Cyde........................................ 27
1.2.4 Calendars and Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
1.2.5 Philosophers in Egypt and Mesopotainia................. 32
1.2.6 Eclipses.................................................. 32
1.2.7 Early Knowledge of Planets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
1.3 Pre-Socratic Greek Astronomy and Cosmology . . . . . . . . . . . . . . . . 38
1.3.1 A Few Milestones........................................ 38
1.3.2 Three Permanent Tendencies ............................ 40
1.3.3 Thales (of Milet) and his Followers, the Milesians........ 42
1.3.4 Pythagoras and the Pythagorians . . . . . . . . . . . . . . . . . . . . . . . . 47
1.3.5 Between Pythagoras and Plato . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2. Classical Greek Astronomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.1 Plato's World . . . . . ....... ... . .... .. .. ... .. . . .. ... ... ... ..... .. . 55
2.1.1 The Myth of the Cave . . .... .. .. ... .. . . .. .. . ... .... .... .. . 55
2.1.2 The Timaeus............................................. 58
2.1.3 The Four Elements....................................... 59
2.1.4 Space.................................................... 60
VIII Contents
2.1.5 Platonic Astronomy ..................................... 63
2.1.6 Concluding our Visit to Plato's Dialogues................ 69
2.2 Plato's Contemporaries: Eudoxus, Callippus................... 70
2.2.1 Eudoxus and his System of Homocentric Spheres. . . . . . . . 70
2.2.2 The Reform of Calippus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
2.2.3 Astronomers at the Time of Aristotle . . . . . . . . . . . . . . . . . . . . 78
2.3 Aristotle's World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
2.3.1 Aristotle's Cosmology ofHomocentric Spheres.......... 79
2.3.2 Aristotle's Physics....................................... 81
2.4 The Legacy of Plato and Aristotle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
2.5 The Heliocentric Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
2.5.1 Heraclides (from the Pontus) ............................ 85
2.5.2 Aristarchus (300-250 BC?) .............................. 86
2.5.3 Seleucus (150-100 BC)................................... 87
2.5.4 The Provisional End of Heliocentrism . . . . . . . . . . . . . . . . . . . 88
2.6 Hipparchus and his Successors up to Ptolemy . . . . . . . . . . . . . . . . . 89
2.6.1 Alexandria as an Intellectual Center;.................... 89
2.6.2 Hipparchus.............................................. 91
2.6.3 From Hipparchus to Ptolemy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
2.6.4 Claudius Ptolemy........................................ 93
2.7 Eccentric and Epicycle Circles: The Ptolemaic Mechanisms.... 94
2.7.1 Solar Motion: The Eccentric System..................... 94
2.7.2 Planetary Motion: The Epicycle-Deferent System........ 95
2.7.3 The Equivalence Between the Two Systems for the Sun... 96
2.7.4 Equivalence of the Two Systems for Mars, Jupiter,
and Saturn .............................................. 97
2.7.5 Was Ptolemy aPrecursor of Copernicus? ................ 101
2.7.6 Elaboration ofthe Epicycle-Deferent System ............. ·103
2.8 The Earth, Sun, Moon, and Planets: Distances and Sizes....... 108
2.8.1 The Phenomena......................................... 108
2.8.2 The Earth's Radius: A Basic Unit of Length . . . . . . . . . . . . . . 109
2.8.3 The Moon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
2.8.4 The Sun: The Aristarchus Determinations............... 113
2.8.5 The Methodology of Hipparchus ........................ 116
2.8.6 Planetary Distances ..................................... 121
2.9 The Precession of Equinoxes .................................. 123
2.9.1 Hipparchus's Discovery ................................. 123
2.9.2 Ptolemy's Precession of Equinoxes ...................... 126
Contents IX
3. Ptolemy's Astronomy Questioned ............................. 129
3.1 The Scientific Genealogy of Ptolemy . . . . . . . . . . . . . . . . . . . . . . . . . .. 129
3.1.1 Ptolemy's Physics............................ ............ 129
3.1.2 The Pagan Followers ofPtolemy ......................... 131
3.1.3 John Philopon .......................... ................. 132
3.1.4 Save the Bible! ................ " . . . . . ... . . . .. . . . . .. . . . . .. 133
3.2 The Church Fathers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 133
3.2.1 The So-Called "Dark Ages" .............................. 133
3.2.2 From Origen to Augustine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 134
3.2.3 Augustine................................................ 137
3.2.4 Astrology................................................ 139
3.2.5 The Debate over Creation and the Meaning ofTime ...... 140
3.2.6 The Seeds of aReborn Science........................... 141
3.3 The Contribution of the Arabic World
to Astronomical Knowledge.................................... 142
3.3.1 Indian Astronomy ....................................... 142
3.3.2 The Development of the Islamic Knowledge of the Sky. .. 143
3.3.3 Alfonso the Tenth and his Time.......................... 150
3.4 The Western World up to Copernicus.......................... 155
3.4.1 The Continuing Heliocentric Temptation. ................ 155
3.4.2 The Era of the Translators ............................... 165
3.4.3 The Priests and Monks of the Church.
The Triangular Battle .................................... 168
3.4.4 The Progress of Observations. . . . . . . . . . . . . . . . . . . . . . . . . . .. 179
4. The Period of the Renaissance. . . . . . . . . . . . . . . .. . . . . . .. . . . .. . . .. 187
4.1 From 1450 to 1600: An Overview............... . ............... 187
4.2 Copernicus and the Determination of Planetary Distances ..... 190
4.2.1 The Heliocentric System as a Working Hypothesis ....... 191
4.2.2 The Distance Scale in the Planetary System.......... .... 195
4.2.3 The Copernican System Elaborated . . . . . . . . . . . . . . . . . . . . .. 202
4.3 The Progress of the Observations; Tycho Brahe
and the Nature of the Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 208
4.3.1 The Supernova of 1572 ................................... 208
4.3.2 The Comet of 1577........ ............................... 210
4.3.3 The Helio-geocentric System of Tycho ........... . . . . . . .. 212
4.4 Kepler and the Death of Circularity . . . . . . . . . . . . . . . . . . . . . . . . . . .. 212
4.4.1 Planetary Distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 214
4.4.2 The Elliptical Motion................................. ... 218
x
Contents
4.4.3 The Elliptical Laws of Motion ............................ 226
4.4.4 The Distances of Planets to the Sun
and Kepler's Third Law .................................. 227
4.4.5 Kepler's Concepts Regarding Dynamics .................. 228
4.4.6 Kepler's Other Studies ................................... 232
4.5 Galileo, Physidst and Ob server. ............................... 233
4.5.1 Pre-Galilean Astronomical Observations ................. 234
4.5.2 Galileo in 1610: The Telescope and the Telescopic World. 242
4.5.3 Galileo's Mechanics ..................................... 250
5. Dynamics Enters Astronomy: From Galileo to Newton ........ 253
5.1 Galilean Dynamics ............................................ 253
5.2 Frands Bacon in England. ..................................... 255
5.3 The French School: Descartes and his Contemporaries ........ 257
5.3.1 Cartesian Mechanics: Huygens and Centrifugal Force .... 257
5.3.2 Descartes' Theory of Vortices and Some Reflections
on Space and Time ...................................... 259
5.3.3 Objections: Henry More and Space; Isaac Barrow
and Time ................................................ 266
5.4 Newton and Universal Gravitation ............................. 267
5.4.1 The Principia ............................................ 268
5.4.2 Kepler's Law of Equal Areas ............................. 269
5.4.3 Newton's Law of Gravitation: The Inverse Square
of Distance .............................................. 271
5.4.4 The Systematization of Mechanics ....................... 274
5.4.5 The Refutation of the Cartesian Theory of Vortices ...... 277
5.5 The Triumph of Newton ....................................... 278
5.5.1 The Development of Instrumental Astronomy ........... 279
5.5.2 The Flattening of the Earth .............................. 283
5.5.3 The Return ofHalley's Comet ........................... 284
5.5.4 The Aberration of Light ................................. 285
5.5.5 Annual Stellar Parallaxes ................................ 286
5.5.6 The Fundamental Distances in the Solar System ......... 290
5.5.7 Newton and God ........................................ 294
5.6 Appendix
Written in Collaboration with Prof. Daniel Pecker ............. 296
5.6.1 Geometrical Preliminaries ............................... 297
5.6.2 Newton's Text Commented .............................. 304
