The Evolving Universe and the Origin of Life

The Evolving Universe and the Origin of Life


Pekka Teerikorpi • Mauri Valtonen • Kirsi Lehto •
Harry Lehto • Gene Byrd • Arthur Chernin

The Evolving Universe and
the Origin of Life
The Search for Our Cosmic Roots

123


Dr. Pekka Teerikorpi
University of Turku
Department of Physics and Astronomy
Tuorla Observatory
FI-21500 Piikki¨o
Finland
pekkatee@utu.fi

Dr. Mauri Valtonen
University of Turku
Department of Physics and Astronomy
Tuorla Observatory
FI-21500 Piikki¨o
Finland
mavalto@utu.fi

Dr. Kirsi Lehto

University of Turku
Department of Biology
Laboratory of Plant Physiology
FI-20014 Turku
Finland
klehto@utu.fi

Dr. Harry Lehto
University of Turku
Department of Physics and Astronomy
Tuorla Observatory
FI-21500 Piikki¨o
Finland
hlehto@utu.fi

Dr. Gene Byrd
University of Alabama
Department of Physics and Astronomy
P.O. Box 870324
Tuscaloosa AL 35487-0324
USA


Dr. Arthur Chernin
Sternberg State Astronomical Institute
Universitetskiy Prospect 13
Moscow
Russia 119899

ISBN 978-0-387-09533-2

e-ISBN 978-0-387-09534-9

Library of Congress Control Number: 2008930766
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Preface

A golden thread runs through the history of humanity – even in prehistory, when
writing was unknown, there was the need to understand, that restless spark within
us. We have written this book for anybody interested in the quest of knowledge –
at least to the extent that he or she wishes to appreciate the main results of science,
which has changed our way of thinking about the world. Born in a society filled
with applications of science and engineering, we often take all this for granted and
do not stop to think of the steps, invisible as they are in the distant past, that had to

be taken before our world emerged.
We take our readers on a voyage from the treasures of the past to the frontiers
of modern science which includes physics, cosmology, and astrobiology. We divide
the presentation into four parts, which approximately correspond to the major waves
of scientific exploration, past to present.
The first wave, The Widening World View arose in Antiquity and re-emerging at
the end of the Middle Ages, was based on visual observations of the world. Quite a
lot was accomplished with the naked eye, together with simple devices and reasoning. Both Ptolemy and Copernicus belonged to this great era. Around 1600, when
the new sun-centered worldview was advancing and the telescope was invented,
Galileo followed by many others, could see deeper and deeper in space. This led,
among other things, to determination of the distance to the Sun and to the other
stars faintly glimmering in the sky. In the twentieth century, remote galaxies were
reached and observing windows other than optical were opened to astronomers.
A parallel wave we call Physical Laws of Nature was powered by the experimental/mathematical approach to physics, started by Galileo as well, and accelerated
by the work of Newton toward modern physics. This wave took us to the realm of
atoms and elementary particles, and together with the parallel astronomical work
finally led to the modern wave of exploration, the Universe, describing the earliest
processes in its origin and expansion from a superdense state 14 billion years ago to
our universe of galaxies today.
In our own times a new and fascinating wave of exploration of the universe began
which we call Life in the Universe, when humanity learned to launch devices and
even people beyond the Earth. One is reminded of the words by Tsiolkovski “The

v


vi

Preface

planet is the cradle of intelligence, but you do not live in the craddle for ever.” Up
to now only the Moon has been visited by humans, but numerous space probes have
delivered new and impressive information about the planets, asteroids, and comets
of the Solar System, and about the Sun itself. Astrobiology, the new interdisciplinary
field of science, has thus received a strong boost forward, as now it has become possible to map in detail the wide range of conditions inside our planetary system and
to see where life might have originated in addition to the Earth. At the same time,
thanks to the advancements in telescopes, astronomers have been able to discover
other planetary systems and the count of known extrasolar planets now reaches hundreds. These developments have given new perspectives for the role of life and the
human race in the universe.
Two decades ago two of the authors (P.T., M.V.) wrote a book in Finnish, published by the Ursa Astronomical Association (“Cosmos – the developing view of the
world”). The present book owes to that one for its general outline and spirit, but its
contents reflect the team of writers with diverse specialties and the many new, even
revolutionary developments in cosmology, space research, and astrobiology during
these years.
In writing the text, we have had in mind a wide range of audience, from laymen
interested in science to students of both humanities and sciences in universities.
Even professional scientists in physics or astronomy may find the historical parts
and astrobiological excursions interesting, while for biologists it may be useful to
refresh their knowledge of other sciences. We write on an accessible level, avoiding
mathematics and detailed explanations. But the fact remains that some subjects of
modern science, in physics, cosmology, and biology as well, are inherently complicated and difficult to describe “simply.” We have either skipped such topics or have
given descriptions requiring some attentive reading. We conclude some chapters
with brief excursions to interesting “frontier” topics, in order to convey the reader a
feeling of what kinds of things fascinate scientists today (strange phenomena of the
microworld, many dimensional worlds, cosmological dark energy, the origin of life,
the greenhouse effect, . . . ).
Finally, teachers may find this book useful for undergraduate college courses,
particularly those who recognize that it is now difficult to divide science into traditional subjects or those who recognize the connections between humanities and the
sciences. To this purpose we provide a Web site document with a listing of interesting Web sites covering the parts of the text plus a collection of short multiple choice
questions divided by subject:

UniverseWeb.doc
We wish to thank several persons who have read parts of the manuscript or
have in other ways helped this project, e.g., by allowing the use of illustrations.
We mention Yuri Baryshev, Andrej Berdyugin, Svetlana Berdyugina, Anthony
Fairall, Andrea Gabrielli, Ismael Gognard, Jennifer Goldman, Sethanne Howard,
Pekka Hein¨am¨aki, Janne Holopainen, Tom Jarrett, Andreas Jaunsen, Michael Joyce,
Hannu Karttunen, Perttu Kein¨anen, Bill Keel, Tapio Korhonen, John Lanoue, JeanPierre Luminet, Seppo Mattila, Chris Mihos, Seppo Mikkola, Markku Muinonen,
Sami Niemi, Kari Nilsson, Pasi Nurmi, Jyri N¨ar¨anen, Georges Paturel, Saul


Preface

vii

Perlmutter, Luciano Pietronero, Laura Portinari, Travis Rector, Rami Rekola, Shane
D. Ross, John Ruhl, Allan Sandage, Markku Sarimaa, Aimo Sillanp¨aa¨ , Francesco
Sylos Labini, Leo Takalo, Gilles Theureau, Malene Thyssen, Luc Viatour, Iiro Vilja,
and Petri V¨ais¨anen.
We are grateful to Harry Blom, Christopher Coughlin, and Jenny Wolkowicki
of Springer-Verlag, New York for very good collaboration and patience during the
preparation process of this book.
Similarly, we thank Prasad Sethumadhavan of SPi Technologies India.
August 2008
The authors



Contents

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii

Part I The Widening World View
1

When Science Was Born . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Prehistoric Astronomy: Science of the Horizon . . . . . . . . . . . . . . . . . . . . . . . 3
Writing on the Sky Vault and on Clay Tablets . . . . . . . . . . . . . . . . . . . . . . . . 5
Constellations and Horoscope Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
The Ionian Way of Thinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Pythagoras Invents the Cosmos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2

Science in Athens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Anaxagoras Makes the Celestial Bodies Mundane . . . . . . . . . . . . . . . . . . . .
The Atomic Doctrine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Plato Establishes the Academy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Universe of Aristotle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13
13
14
15
18

3

Planetary Spheres and the Size of the Universe . . . . . . . . . . . . . . . . . . . . .
The Theory of Concentric Spheres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Epicycle Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hipparchus Discovers the Slow Wobbling of the Celestial Sphere . . . . . . .

Ptolemy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Size of the Spherical Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Aristarchus of Samos – The Copernicus of Antiquity Enlarging the
Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
On the Road Toward the Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23
23
26
26
28
29
31
34

Medieval Cosmology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Treasures of the Past . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Cosmology of the Middle Ages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Scholasticism: The Medieval Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

37
38
38
40

4

ix

x

Contents

Infinity Where the Center Is Everywhere . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
. . . Or Where There Is No Center . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5

The Roots of the Copernican Revolution . . . . . . . . . . . . . . . . . . . . . . . . . .
Years Under the Italian Sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
De Revolutionibus Appears: The Mission Is Complete . . . . . . . . . . . . . . . . .
Why Put Away the Good Old World? Why Copernicus and Why in the
Sixteenth Century? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Old and New . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Order and Scale of the Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Copernican Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

47
47
49

6

The True Laws of Planetary Motion Revealed . . . . . . . . . . . . . . . . . . . . . .
Tycho Brahe’s Nova Lights the Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tycho’s World Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Kepler’s Mysterious Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Paths of Brahe and Kepler Intersect . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The New Laws of Cosmic Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Orbits and Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

57
57
59
59
62
63
65

7

Galileo Galilei and His Successors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Observation and Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The First Steps into Deep Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fighting on Two Fronts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cartesian Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introducing Accurate Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Developing Telescope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

67
67
70
72
73
74
75

8

How Far Away Are the Stars? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Galileo and the Annual Parallax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bradley Discovers the Aberration of Light . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fifty Years Earlier: Rømer and the Speed of Light . . . . . . . . . . . . . . . . . . . .
Instrumental Advances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rebirth of Galileo’s Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Race Toward Stellar Distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A Three-Dimensional Look at the Winter Sky: Sirius, Stars of Orion,
and Aldebaran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
What If All Stars Were Like the Sun? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

79
79
81
83
84
85
86

The Scale of the Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A Hint from the Cathedral of San Petronio . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using Mars as an Intermediary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transits of Venus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Size of the Earth 2,200 Years After Eratosthenes . . . . . . . . . . . . . . . . . .
The Modern View of the Scale of the Solar System . . . . . . . . . . . . . . . . . . . .

93
93
94
95
97

98

9

49
51
53
54

89
90


Contents

xi

Part II Physical Laws of Nature
10 Newton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
From Woolsthorpe to Principia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Newton’s Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Nature of Gravitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
11 Celestial Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Discovery of Uranus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
The Race to Discover Neptune . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
More Planetary Perturbations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Laplace’s World View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
The Three Body Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Orbits of Comets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
12 Nature of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Light as a Wave Phenomenon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Spectral Analysis – Toward the Physics of Stars . . . . . . . . . . . . . . . . . . . . . . 128
More Information from a Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
13 Electricity and Magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Nature of Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Electricity and Magnetism are Combined . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
Force Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Electromagnetic Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
14 Time and Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
The Strange Speed of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Albert Einstein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
Four-Dimensional World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Time Dilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Mass and Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Principle of Relativity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
15 Curved Space and Gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Discovery of Non-Euclidean Geometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Properties of Non-Euclidean Geometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
The Significance of the Curvature of Space . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Consequences of the General Theory of Relativity . . . . . . . . . . . . . . . . . . . . 163
Strange Properties of Black Holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
Gravitational Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
16 Atoms and Nuclei . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
Conservation of Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
Developments in Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
The Periodic Table of Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175


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Discovery of the Electron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Toward the Atomic Nucleus: Radioactivity . . . . . . . . . . . . . . . . . . . . . . . . . . 180
Rutherford Discovers the Nucleus of the Atom . . . . . . . . . . . . . . . . . . . . . . . 182
17 Strange Microworld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
Particles and Waves Unite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
The Bohr Atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Mechanics of Atoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
Nebulous Particle: Heisenberg’s Uncertainty Principle . . . . . . . . . . . . . . . . . 191
The Structure of Atoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
Common Sense and Reality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
18 Elementary Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Nuclear Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Phenomena of Atomic Nuclei and the Weak Force . . . . . . . . . . . . . . . . . . . . 201
Particles and Accelerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
Quark: At Last the Fundamental Building Block? . . . . . . . . . . . . . . . . . . . . . 207
Messengers of the Weak Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
An Excursion Still Deeper: Does Gravity Live in Many Dimensions? . . . . 211
Part III The Universe
19 Stars: Cosmic Fusion Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Spectral Classification of Stars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Dwarfs and Giants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Internal Structure of a Typical Main Sequence Star, the Sun . . . . . . . . . . . . 222
Life After the Main Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
Little Green Men or White Dwarfs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
Routes to White Dwarfs and Neutron Stars . . . . . . . . . . . . . . . . . . . . . . . . . . 226
Still Denser: Neutron Stars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
The Crab Nebula: A Result of Supernova Explosion . . . . . . . . . . . . . . . . . . . 229
X-Rays and Black Holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231

20 The Riddle of the Milky Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Ideas in Antiquity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Belt of Stars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
Toward the Three-Dimensional Milky Way . . . . . . . . . . . . . . . . . . . . . . . . . . 237
William Herschel’s Milky Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
Great Star Catalogs and Kapteyn’s Universe . . . . . . . . . . . . . . . . . . . . . . . . . 241
Cepheid Variable Stars: Standard Candles to Measure Large Distances . . . 244
Shapley’s Second Copernican Revolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
Cosmic Dust Between the Stars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
The Milky Way Rotates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
The Sun in a Spiral Arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251


Contents

xiii

21 Entering the Galaxy Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
Messier’s Catalog of Nebulae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
The Garden of Nebulae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
John Herschel Goes into Astronomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
Astrophysics Is Born . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
“Island Universes” Gain Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
“The Great Debate” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
Hubble Finds Cepheids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Hubble’s Classification of Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
The Hubble Law of Redshifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
How to Measure Cosmic Distances? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
And Yet It Moves! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
22 Large-scale Structure of the Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281

Galaxy Clustering in Our Neighborhood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Toward Larger Scales: Mapping Three-Dimensional Structures . . . . . . . . . 283
The Novel Realm of Large-Scale Structures . . . . . . . . . . . . . . . . . . . . . . . . . . 286
Hierarchies and Fractals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
Where Uniformity Begins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
23 Finite or Infinite Universe: Cosmological Models . . . . . . . . . . . . . . . . . . . 291
Ancient Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
Newton and the Infinite Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
The Uniform Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
Einstein’s Finite Unchanging Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
Friedmann World Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
The Gallery of Possible Worlds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
The Accelerating Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
Redshift and Cosmic Distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
Topology of Space: Still Another Cause of Headache . . . . . . . . . . . . . . . . . . 304
24 When it all Began: Big Bang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
Deducing the Existence and Properties of the Hot Big Bang . . . . . . . . . . . . 309
Creating Light Elements in the Big Bang . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
Cosmic Background Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
Temperature, Matter, and Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
Astronomical Time Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
Measuring the Geometry of Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
The Origin of Helium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
The First Second . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
The Mystery of the Big Bang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
Inflation and Cosmic World Periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
Antigravity, Cosmic Vacuum, and Dark Energy . . . . . . . . . . . . . . . . . . . . . . . 323
The Very Beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

xiv

Contents

25 The Dark Side of the Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
Discovery of Dark Matter in the Coma Cluster . . . . . . . . . . . . . . . . . . . . . . . 325
Dark Matter in Spiral Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
New Methods of Detecting Dark Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
What Could All that Dark Stuff Be? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
Still Darker: Dark Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332
The Four Fundamental Elements: Some Concluding Thoughts . . . . . . . . . . 332
26 Active Galaxies: Messages Through Radio Waves . . . . . . . . . . . . . . . . . . 335
Early Years of Radio Astronomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
Spectral Lines of Radio Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
Radio Galaxies are Discovered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
Discovery of Quasars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
The Redshift Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
What is Behind the Huge Power of Quasars? . . . . . . . . . . . . . . . . . . . . . . . . . 344
Light Variations and Higher Resolutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
Gravitational Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
Quasars and Their Relatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
27 Origin of Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
Cosmic Eggs or Cosmic Seeds? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
From Density Condensations to Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
We Need Dark Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
Formation of Large Scale Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
Generations of Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
The Young Milky Way and Stellar Populations . . . . . . . . . . . . . . . . . . . . . . . 359
How Old is Our Milky Way? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
The Changing Milky Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

Part IV Life in the Universe
28 The Nature of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
Life and the Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
Our Changing Views of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
The Basic Structures and Functions of Life . . . . . . . . . . . . . . . . . . . . . . . . . . 370
Chemistry of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
The Discovery of Genetics and Its Chemical Basis . . . . . . . . . . . . . . . . . . . . 373
The Genetic Code and Its Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
Genetics and the Evolution of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
The Central Features of Life are Derived from the Same Origin . . . . . . . . . 383
Environmental Requirements of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
General Principles of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
Still Deeper into the Biochemical World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389


Contents

xv

29 The Origin of Earth and its Moon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
Historic Estimates of the Age of the Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
Conflict of Cooling Ages with Sedimentation Ages and Its Resolution
by Radioactivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
Discovery of Tectonic Plate Motions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
Origin of the Earth as Part of the Solar System, a Modern View . . . . . . . . . 400
The Early Earth and the Origin of the Moon . . . . . . . . . . . . . . . . . . . . . . . . . 402
Evolution of Earth and the Relevant Timescales . . . . . . . . . . . . . . . . . . . . . . 403
Plate Motions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
Structure of the Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
Climate, Atmosphere and, the Greenhouse Effect . . . . . . . . . . . . . . . . . . . . . 408

30 Emergence and Evolution of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
Chemicals and Structures of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
RNA World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
Conditions on the Early Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
Prebiotic Synthesis of the Building Blocks of Life . . . . . . . . . . . . . . . . . . . . 414
The Riddle of Prebiotic Assembly of Polymers . . . . . . . . . . . . . . . . . . . . . . . 418
Production of the Genetic Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420
The Final Step: Formation of Cellular Life . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
Evolution of the Biosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
Effects of Life on the Atmosphere and Climate . . . . . . . . . . . . . . . . . . . . . . . 426
Catastrophes Affecting the Evolution of the Biosphere . . . . . . . . . . . . . . . . . 429
Benefits of Catastrophes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
31 Life and our Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433
An Overview of Unlikely and Likely Suspects for Life (And Why) . . . . . . 433
Mars, a Likely Suspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
Missions to Mars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439
The Viking Landers Searching for Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
Possibilities for Life on Mars and Signs of Water . . . . . . . . . . . . . . . . . . . . . 442
Histories of Life on Mars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
Venus – Hot and Dry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
Space Missions to Venus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
A Brief Look at Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
Jupiter – a Gas Giant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
The Active Io . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
Europa – Ice World with Prospects for Life . . . . . . . . . . . . . . . . . . . . . . . . . . 453
Saturn: The Gas Giant with Prominent Rings . . . . . . . . . . . . . . . . . . . . . . . . . 455
Titan – the Moon with Its Own Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . 456
The Outer Realms of the Solar System – Cold and Lonely . . . . . . . . . . . . . . 458
Comets and Asteroids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459

xvi

Contents

32 Extrasolar Planetary Systems and Life in other Solar Systems . . . . . . . 461
The Increasing Number of Planets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
Astrometric and Velocity Attempts to Detect Extrasolar Planets . . . . . . . . . 462
Other Detection Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465
Characteristics of Extrasolar Planets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
Binary Stars and Planets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
Understanding Planetary Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
Are Any Exoplanets Suitable for Life? Habitable Zones . . . . . . . . . . . . . . . . 471
Survivability of Earths and How to Detect a Life-bearing Planet . . . . . . . . . 473
We are Here . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
Radio SETI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475
The Drake Equation Or “Is There Really Anybody out There?” . . . . . . . . . 476
The Fermi Paradox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
33 Human’s Role in the Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479
Immense Space, Deep Time, and Common Life . . . . . . . . . . . . . . . . . . . . . . 479
On the Other Hand, a Fine-Tuned Universe with Unique Life? . . . . . . . . . . 481
Natural Laws and Universal Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
Focus on the Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485
Life Affecting Itself and Its Planet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486
A Matter of Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
Recommended Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493


List of Tables

3.1
5.1
6.1
9.1
9.2
12.1
19.1
19.2
19.3
21.1
23.1
23.2
28.1
28.2
29.1
29.2
31.1
31.2

Synodic and sidereal periods for the planets (including those
discovered in modern times) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Copernicus’ values for the minimum, average, and maximum solar
distances of the planets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
The orbital values as calculated by Kepler to check his Third Law . . . . . 64
Derived values of the solar distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Data on the orbits of planets (plus the dwarf planet Pluto) . . . . . . . . . . . . 98
Relative proportions (by mass) of chemical elements in the Sun, the
Earth, and the human body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Current internal properties of the Sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

Energy-generating nuclear reactions in stars . . . . . . . . . . . . . . . . . . . . . . . 224
Comparison of properties of the Sun and white dwarfs . . . . . . . . . . . . . . 226
Measured distances to the Andromeda galaxy . . . . . . . . . . . . . . . . . . . . . . 277
Friedmann models of the universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
Redshift, light travel time distance, and “distance now” . . . . . . . . . . . . . . 303
Genetic code: Correspondence of the nucleotides triplets and the
amino acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
Number of ribosomal components in eukaryota and prokaryota . . . . . . . 379
Isotopes in common use in dating minerals . . . . . . . . . . . . . . . . . . . . . . . . 396
Geologic times (in millions of years) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
Physical properties of the planets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
Atmospheric and surface properties of the inner planets . . . . . . . . . . . . . 450

xvii



Part I: The Widening World View



Chapter 1

When Science Was Born

Thomas Henry Huxley, the eminent British zoologist of the nineteenth century once
wrote: “For every man the world is as fresh as it was at the first day.” This realization
beautifully connects us with ancient minds. It is the same world which puzzles us
now, even though we observe it to distances of billions of light years with modern
telescopes on Earth and in space, and we penetrate into the incredibly small microworld using microscopes and particle accelerators. These observations and our

current knowledge of the workings of the universe are the fruition of a long chain of
scientific enquiry extending back into prehistoric times–when the only instrument
was the naked eye and the world was fresh.

Prehistoric Astronomy: Science of the Horizon
The Egyptians noted the stars that appeared to attend the birth of the Sun in the eastern morning sky. These were different at different seasons. One star was especially
important, Sirius, the brightest star in the sky, in the constellation Canis Major, the
Great Dog. Around 3000 BC, this “Dog Star” appeared every summer in the eastern sky before dawn. The day of each year when it was viewed the first time, the
so-called heliacal rising above the horizon, marked the start of the calendar year in
Egypt. This very important event heralded the longed for flood of the Nile, on which
agriculture and life depended.
The horizon was a fascinating thing for ancient people. They viewed it as a sort of
boundary of the world. “Horizon” comes from the Greek word meaning “to bound.”
In the Finnish language it is romantically “the coastline of the sky” (taivaanranta).
In addition to the Sun’s daily motion across the sky, during the year, the places on
the horizon where it rises in the morning and sets in the evening shift slowly. As
winter progresses to summer, these points on the horizon move from south to north.
The Sun remains visible longer and ascends higher in the sky. The day when the
sunrise and sunset points are farthest to the north in the horizon and the Sun ascends highest in the sky is the summer solstice (solstice meaning “Sun stand still”
P. Teerikorpi et al., The Evolving Universe and the Origin of Life
c Springer Science+Business Media, LLC 2009

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1 When Science Was Born

Fig. 1.1 Stonehenge is an impressive monument of Bronze Age interest in celestial events at the

horizon (photograph by Harry Lehto)

in Latin). Similarly, there is a day, the winter solstice, when the day is the shortest,
and the sunrise happens closest to the south. These and other points on the horizon
had both practical and ritual significance. For example, the ancient Hopi people, living in their pueblos in Arizona, used (and still use) the horizon with its sharp peaks
and clefts as a convenient agricultural and ceremonial calendar (e.g., the position of
the rising Sun indicated when the corn should be planted).
Around the world there are archeological remains dating from thousands of years
ago, which seem to have been made to worship, view, and even predict particular
celestial events. The pyramids of Egypt may have originally been built to symbolize
the Sun god who every morning was reborn in the eastern horizon, a place called
“akhet” by the ancient Egyptians. Everybody knows of Stonehenge, one of the wonders of the Bronze Age world in the plain of Salisbury, a hundred kilometers from
modern London (Fig. 1.1). It is made of concentric structures of stones and pits, the
youngest of which, with the familiar great stones 6.5 m high, dates from about 2000
BC. The rather complex assemblage is surrounded by a ditch that forms a circle
104 m in diameter.
The axis of Stonehenge points at the sunrise direction on midsummer morning.
For a person standing in the middle of this monument the disc of the Sun appears
just above what is called the “heel stone” 60 m away. Stonehenge may have served
other astronomical purposes, too. Its large circles were built first, and may have been
directly related to interesting horizon points, while the later structures made of big
stones may have had ceremonial significance, perhaps also symbolizing the horizon
circle. The great effort needed to make Stonehenge testifies to the status given to
horizon phenomena at that time.
A few years ago in Germany, a large circle formation was discovered in a wheat
field which archeologists recognized as a Stone Age “observatory of the horizon.”
When in use, the 75-m circle had three gates, one of which looked to the north
(Fig. 1.2). Two southern gates were so directed that on the winter solstice an observer standing at the center of the circle saw the Sun rising and setting at its southernmost horizon points through the gates. This remarkable structure in Goseck is
about 7,000 years old. So 2,000 years before the builders started their work at Stonehenge, people in the continent were busy making horizon circles!

Writing on the Sky Vault and on Clay Tablets

5

Fig. 1.2 A sketch of the large
7,000-year-old circle formation in Goseck, Germany.
Two southern gates were so
directed that on the winter solstice the observer in the center
saw the Sun rising and setting through the gates (credit:
Rainer Zenz/Wikipedia)

Archeoastronomers have found traces of horizon science all around the world.
For example, on Easter Island in the middle of the Pacific Ocean, the famous stone
statues standing on great platforms are often directed according to astronomically
significant horizon points. For its natives, this island was “the eye that looks at
the sky.” People everywhere have been fascinated by regularly appearing celestial
phenomena, have patiently noted their rhythms, and even have arranged their lives
according to them. In this way, our ancestors paved the way for modern astronomy,
modern science, and even modern life.

Writing on the Sky Vault and on Clay Tablets
At every point of history, mankind has made the best of what the environment had
to offer for living. When the conditions changed, like during the ice ages, human
cultures adopted new ways of living as a response to those changes. Sometimes
unexpected things resulted. An example is the formation of the fertile delta region
between the Euphrates and Tigris rivers flowing into the Persian Gulf. When the
surface of the Gulf gradually rose tens of meters after the Ice Age, the flow of the two
rivers slowed making the region good for farming. However, when the climate got
dryer around 3500 BC, large scale irrigation became important and power became

centralized in Sumerian cities. Life was centered on the temple, dedicated to the god
of that city. The temples were large administrative and economic centers, headed by
the clergy. The polytheistic religion of Sumer was inherited by Babylonia around
1500 BC.
Writing had been invented around 3000 BC by Sumerians. It started a flow of
unexpected cultural evolution. The art of cuneiform writing was originally useful for
bookkeeping in the economic centers, temples, but it gradually found application in
many other fields than business, including sky watching. How celestial bodies move
gives us both ancient and modern methods of timekeeping. We know that Sumerian
clergy tracked the Moon to build a lunar calendar by recording the information on
clay tablets.


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1 When Science Was Born

However, their direct descendents, the Babylonian priests, were instead curious
to learn what signs the divine celestial stage offered about the future of the rulers
and the kingdom. The sky formed a huge screen with “texts” that the specialist tried
to interpret. Thus, systematic astrology was born, together with a developed state.
Interest in the misty future was strong and there were also other methods of prediction, like watching the flight of birds. In contrast to today, at that time astrology was
quite a rational undertaking when stars were viewed as gods or their representatives.
It was logical to try to find links between celestial phenomena and earthly happenings. Some were indeed known: the seasons are marked by the path of the Sun
among the stars and tides obey the Moon. With little artificial light to block their
view, the ancients were much more observant of the sky than most people today.
In Mesopotamia, a lunar calendar was based on the phases of the Moon. Each
month began on that evening when the thin sickle of the growing Moon was first
seen after sunset. Nowadays, the solar calendar (which is consistent with the seasons) dominates everyday life, but the lunar calendar is still important for religious
purposes.

Because of the yearly cycle of the Sun, different constellations are visible in the
evening at different seasons. The appearance of the sky today is almost the same as
thousands of years ago. Many constellations still carry the names that shepherds or
seamen once gave them. Certainly the starry patterns initially had real meaning. Various animals, gods, and mythical heroes were permanently etched on the sky. But
the constellations also form a map that helps one to identify the place where something happens in the sky. In modern astronomy, there are 88 constellations with definite borders. For instance, when comet Halley last appeared, one could read in the
newspaper that in December 1985 the visitor would be in the constellation of Pisces
just south of Pegasus. With this information it was easy to spot the famous comet
through binoculars. The daily motion of the Earth merely caused the comet and the
constellation to move together across the sky, keeping their relative positions.
The Babylonian astrologers were well aware that not all celestial objects move
faithfully together with the stars. The Moon shifts about 13◦ (or 26 times its own
diameter) eastward relative to the stars every day. It takes a little more than 27 days
for the Moon to come back roughly to the same place again among the stars. Also
the Sun moves relative to the stars although the glare blots them out. However,
during the year, different constellations are visible near the Sun just before sunrise
or a little after sunset. Thus it was deduced that the Sun moves around the sky
visiting the same constellations through the year. Astrologers divided its route, or
the ecliptic, into 12 equal parts and the Sun stayed in each for about one month.
These constellations came to define the signs of the zodiac. The word ecliptic means
the solar path where the eclipses occur.

Constellations and Horoscope Signs
About 2,000 years ago, the signs of the zodiac (familiar from newspaper horoscopes) and the actual constellations corresponded to each other. This is not so any