Table Of Content21st CENTURY ASTRONOMY
FOURTH EDITION
Laura Kay, Stacy Palen, Brad Smith, and George Blumenthal
F O U RT H E D I T I O N
21ST CENTURY
ASTRONOMY
FOURTH EDITION
21ST CENTURY
ASTRONOMY
LAURA KAY (cid:116) Barnard College
STACY PALEN (cid:116) Weber State University
BRAD SMITH (cid:116) Santa Fe, New Mexico
GEORGE BLUMENTHAL (cid:116) University of California—Santa Cruz
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Copyright © 2013 by Laura Kay, Stacy Palen, Bradford Smith, and George Blumenthal.
Copyright © 2010 by Jeff Hester, Bradford Smith, George Blumenthal, Laura Kay, and Howard G. Voss.
Copyright © 2007 by Jeff Hester, David Burstein, George Blumenthal, Ronald Greeley, Bradford Smith, and Howard G. Voss.
Copyright © 2002 by Jeff Hester, David Burstein, George Blumenthal, Ronald Greeley, Bradford Smith, Howard G. Voss, and
Gary Wegner.
Since this page cannot accommodate all the copyright notices, the Credits pages, starting on p. C1, constitute an extension of
the copyright page.
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Laura Kay thanks her partner, M.P.M. She dedicates this
book to her late uncle, Lee Jacobi, for an early introduction
to physics, and to her late colleagues at Barnard College,
Tally Kampen and Sally Chapman.
Stacy Palen thanks the wonderful colleagues in her depart-
ment and the crowd at Bellwether Farm, all of whom made
room for this project in their lives, even though it wasn’t their
project.
Brad Smith dedicates this book to his patient and under-
standing wife, Diane McGregor.
George Blumenthal gratefully thanks his wife, Kelly Weisberg,
and his children, Aaron and Sarah Blumenthal, for their sup-
port during this project. He also wants to thank Professor
Robert Greenler for stimulating his interest in all things
related to physics.
Brief Contents
Part I Introduction to Astronomy
Chapter 1 Why Learn Astronomy?(cid:3)3
Chapter 2 Patterns in the Sky—Motions of Earth(cid:3)25
Chapter 3 Motion of Astronomical Bodies(cid:3)63
Chapter 4 Gravity and Orbits(cid:3)89
Chapter 5 Light(cid:3)117
Chapter 6 The Tools of the Astronomer(cid:3)151
Part II The Solar System
Chapter 7 The Birth and Evolution of Planetary Systems(cid:3)185
Chapter 8 The Terrestrial Planets and Earth’s Moon(cid:3)215
Chapter 9 Atmospheres of the Terrestrial Planets(cid:3)257
Chapter 10 Worlds of Gas and Liquid—The Giant Planets(cid:3)291
Chapter 11 Planetary Adornments—Moons and Rings(cid:3)323
Chapter 12 Dwarf Planets and Small Solar System Bodies(cid:3)359
Part III Stars and Stellar Evolution
Chapter 13 Taking the Measure of Stars(cid:3)395
Chapter 14 Our Star—The Sun(cid:3)427
Chapter 15 Star Formation and the Interstellar Medium(cid:3)459
Chapter 16 Evolution of Low-Mass Stars(cid:3)491
Chapter 17 Evolution of High-Mass Stars(cid:3)521
Chapter 18 Relativity and Black Holes(cid:3)551
Part IV Galaxies, the Universe, and Cosmology
Chapter 19 The Expanding Universe(cid:3)581
Chapter 20 Galaxies(cid:3)611
Chapter 21 The Milky Way—A Normal Spiral Galaxy(cid:3)641
Chapter 22 Modern Cosmology(cid:3)667
Chapter 23 Large-Scale Structure in the Universe(cid:3)695
Chapter 24 Life(cid:3)723
vi
Contents
Preface(cid:3)xxv
About the Authors(cid:3)xxxiv
Introduction to Astronomy
PART I
Chapter 1 Why Learn Astronomy?(cid:4) 3
1.1 Getting a Feel for the Neighborhood(cid:3)4
1.2 Astronomy Involves Exploration and Discovery(cid:3)7
1.3 Science Is a Way of Viewing the World(cid:3)9
Process of Science: The Scientific Method(cid:3)1 0
1.4 Patterns Make Our Lives and Science Possible(cid:3)13
Math Tools 1.1 Mathematical Tools(cid:3)15
Math Tools 1.2 Reading a Graph(cid:3)16
1.5 Thinking like an Astronomer: What Is a Planet?(cid:3)17
1.6 Origins: An Introduction(cid:3) 17
Summary(cid:3) 18
Unanswered Questions(cid:3) 18
Questions and Problems(cid:3) 18
Exploration: Logical Fallacies(cid:3)23
Chapter 2 Patterns in the Sky—Motions of Earth(cid:4) 25
2.1 A View from Long Ago(cid:3) 26
2.2 Earth Spins on Its Axis(cid:3) 27
Connections 2.1 Relative Motions and Frame of Reference(cid:3) 28
Math Tools 2.1 How to Estimate the Size of Earth(cid:3) 37
2.3 Revolution about the Sun Leads to Changes during the Year(cid:3) 37
Process of Science: Theories Must Fit All the Known Facts(cid:3)42
2.4 The Motions and Phases of the Moon(cid:3)45
2.5 Cultures and Calendars(cid:3)49
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viii CONTENTS
2.6 Eclipses: Passing through a Shadow(cid:3) 50
2.7 Origins: The Obliquity of Earth(cid:3)55
Summary(cid:3)56
Unanswered Questions(cid:3) 57
Questions and Problems(cid:3) 57
Exploration: The Phases of the Moon(cid:3) 61
Chapter 3 Motion of Astronomical Bodies(cid:4) 63
3.1 The Motions of Planets in the Sky(cid:3) 64
3.2 Earth Moves(cid:3) 65
Connections 3.1 How Copernicus Scaled the Solar System(cid:3) 66
Math Tools 3.1 Sidereal and Synodic Periods(cid:3) 68
3.3 An Empirical Beginning: Kepler’s Laws(cid:3)69
Process of Science: Theories Are Falsified(cid:3)71
Math Tools 3.2 Kepler’s Third Law(cid:3)74
3.4 Galileo: The First Modern Scientist(cid:3)75
3.5 Newton’s Laws of Motion(cid:3) 76
Math Tools 3.3 Proportionality(cid:3) 79
Math Tools 3.4 Using Newton’s Laws(cid:3) 81
3.6 Origins: Planets and Orbits(cid:3) 82
Summary(cid:3) 82
Unanswered Questions(cid:3) 83
Questions and Problems 83
Exploration: Kepler’s Laws(cid:3) 87
Chapter 4 Gravity and Orbits(cid:4) 89
4.1 Gravity Is a Force between Any Two Objects Due to Their
Masses(cid:3) 90
Process of Science: Universality(cid:3) 91
Math Tools 4.1 Playing with Newton’s Laws of Motion and Gravitation(cid:3) 94
Connections 4.1 Gravity Differs from Place to Place within an Object(cid:3)96
4.2 Orbits Are One Body “Falling around” Another(cid:3)97
Math Tools 4.2 Circular Velocity and Orbital Periods(cid:3) 100
Math Tools 4.3 Calculating Escape Velocities(cid:3) 102
4.3 Tidal Forces on Earth(cid:3)103
Math Tools 4.4 Tidal Forces(cid:3) 105
4.4 Tidal Effects on Solid Bodies(cid:3) 108
