he T Cosmic Perspective

A01_BENN9068_08_NASTA_FM.indd 1 02/03/17 9:34 AM Astronauts get a unique opportunity to experience a cosmic perspective. Here, astronaut John Grunsfeld has a CD of The Cosmic Perspective floating in front of him while orbiting Earth during the Space Shuttle’s final servicing mission to the Hubble Space Telescope (May 2009).

A01_BENN9068_08_NASTA_FM.indd 2 02/03/17 9:34 AM he T Cosmic Perspective Eighth Edition

Jeffrey Bennett University of Colorado at Boulder Megan Donahue Michigan State University Nicholas Schneider University of Colorado at Boulder Mark Voit Michigan State University

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A01_BENN9068_08_NASTA_FM.indd 3 02/03/17 9:34 AM Editor-in-Chief: Jeanne Zalesky Compositor: Cenveo Publisher Services Executive Editor: Nancy Whilton Design Manager: Mark Ong Director of Marketing: Christy Lesko Interior and Cover Designer: Preston Thomas Marketing Manager: Elizabeth Ellsworth Illustrations: Rolin Graphics Program Manager: Mary Ripley Photo Research: Amy Dunleavy Project Manager: Chandrika Madhavan Photo Research Management: Maya Gomez Program and Project Management Team Lead: Media Producer: Jenny Moryan Kristen Flathman Manufacturing Buyer: Maura Zaldivar-Garcia Copyeditor: Lifland et al., Bookmakers Printer and Binder: Courier Kendallville Production Service: Lifland et al., Bookmakers

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Library of Congress Cataloging-in-Publication Data

Names: Bennett, Jeffrey O. Title: The cosmic perspective / Jeffrey Bennett [and three others]. Description: Boston : Pearson, [2017] | Includes index. Identifiers: LCCN 2015041654 Subjects: LCSH: Astronomy—Textbooks. Classification: LCC QB43.3 .C68 2017 | DDC 520–dc23 LC record available at http://lccn.loc.gov/2015041654

ISBN-10: 0-13-475266-X (High School Binding) ISBN-13: 978-0-13-475266-2 (High School Binding)

www.PearsonSchool.com/Advanced 1 2 3 4 5 6 7 8 9 10—V311—20 19 18 17 16

A01_BENN9068_08_NASTA_FM.indd 4 02/03/17 9:34 AM Dedication

To all who have ever wondered about the mysteries of the universe. We hope this book will answer some of your questions—and that it will also raise new questions in your mind that will keep you curious and interested in the ongoing human adventure of astronomy. And, especially, to Michaela, Emily, Sebastian, Grant, Nathan, Brooke, and Angela. The study of the universe begins at birth, and we hope that you will grow up in a world with far less poverty, hatred, and war so that all people will have the opportunity to contemplate the mysteries of the universe into which they are born.

A01_BENN9068_08_NASTA_FM.indd 5 02/03/17 9:34 AM Brief Contents

PART I PART IV DEVELOPING PERSPECTIVE A DEEPER LOOK AT NATURE

1 A MODERN VIEW OF THE UNIVERSE 1 S2 SPACE AND TIME 400 2 DISCOVERING THE UNIVERSE S3 SPACETIME AND GRAVITY 422 FOR YOURSELF 24 S4 BUILDING BLOCKS OF THE UNIVERSE 445 3 THE SCIENCE OF ASTRONOMY 53 S1 CELESTIAL TIMEKEEPING AND NAVIGATION 84 PART V STARS

PART II 14 oUR STAR 466 KEY CONCEPTS FOR ASTRONOMY 15 SURVEYING THE STARS 488 16 STAR BIRTH 513 4 MAKING SENSE OF THE UNIVERSE: UNDERSTANDING MOTION, ENERGY, 17 STAR STUFF 534 AND GRAVITY 110 18 THE BIZARRE STELLAR GRAVEYARD 557 5 LIGHT AND MATTER: READING MESSAGES FROM THE COSMOS 137 PART VI 6 TELESCOPES: GALAXIES AND BEYOND PORTALS OF DISCOVERY 165 19 oUR GALAXY 580 20 GALAXIES AND THE FOUNDATION OF MODERN PART III COSMOLOGY 604 LEARNING FROM OTHER WORLDS 21 GALAXY EVOLUTION 627 7 oUR PLANETARY SYSTEM 190 22 THE BIRTH OF THE UNIVERSE 648 8 FORMATION OF THE SOLAR SYSTEM 214 23 DARK MATTER, DARK ENERGY, AND THE FATE OF THE UNIVERSE 669 9 PLANETARY GEOLOGY: EARTH AND THE OTHER TERRESTRIAL WORLDS 233 PART VII 10 PLANETARY ATMOSPHERES: EARTH AND THE OTHER LIFE ON EARTH AND BEYOND TERRESTRIAL WORLDS 270 24 LIFE IN THE UNIVERSE 698 11 JOVIAN PLANET SYSTEMS 310 Credits C-1 12 ASTEROIDS, COMETS, AND Appendixes A-1 DWARF PLANETS: THEIR NATURE, ORBITS, AND IMPACTS 341 Glossary G-1 13 oTHER PLANETARY SYSTEMS: Index I-1 THE NEW SCIENCE OF DISTANT WORLDS 370

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A01_BENN9068_08_NASTA_FM.indd 6 02/03/17 9:34 AM Detailed Contents

Preface xii Cosmic Context Figure 2.15: The Seasons 34 About the Authors xxii Common Misconceptions: High Noon 36 How to Succeed in Your Astronomy Course xxiv Common Misconceptions: Sun Signs 38 Common Misconceptions: Shadows and the Moon 40 Foreword by Neil deGrasse Tyson xxvi Common Misconceptions: The “Dark Side” of the Moon 41 Common Misconceptions: Moon in the Daytime PART I and Stars on the Moon 42 Developing Perspective Special Topic: Does the Moon Influence Human Behavior? 45 Special Topic: Who First Proposed a Sun-Centered 1 a MODERN VIEW OF THE UNIVERSE 1 Solar System? 48 1.1 The Scale of the Universe 2 1.2 The History of the Universe 11 3 the SCIENCE OF ASTRONOMY 53 1.3 Spaceship Earth 14 3.1 The Ancient Roots of Science 54 1.4 The Human Adventure of Astronomy 19 3.2 Ancient Greek Science 59 Exercises and Problems 21 3.3 The Copernican Revolution 63 3.4 The Nature of Science 69 Common Misconceptions: The Meaning of a Light-Year 6 3.5 Astrology 77 Mathematical Insight 1.1: How Far Is a Light-Year? An Exercises and Problems 81 Introduction to Astronomical Problem Solving 6 Special Topic: How Many Planets Are There in Our Solar Special Topic: Aristotle 61 System? 8 Common Misconceptions: Columbus and Mathematical Insight 1.2: The Scale of a Flat Earth 62 Space and Time 9 Special Topic: Eratosthenes Measures Earth 62 Common Misconceptions: Confusing Very Mathematical Insight 3.1: Eccentricity and Planetary Different Things 10 Orbits 68 Mathematical Insight 1.3: Order of Magnitude Mathematical Insight 3.2: Kepler’s Third Law 70 Estimation 10 Cosmic Context Figure 3.25: The Copernican Cosmic Context Figure 1.10: Our Cosmic Origins 12 Revolution 72 Mathematical Insight 1.4: Speeds of Rotation and Special Topic: And Yet It Moves 74 Orbit 16 Common Misconceptions: Eggs on the Equinox 75 Special Topic: Logic and Science 75 2 DISCOVERING THE UNIVERSE Extraordinary Claims: Earth Orbits the Sun 77 FOR YOURSELF 24

2.1 Patterns in the Night Sky 25 S1 celestial TIMEKEEPING AND NAVIGATION 84 2.2 The Reason for Seasons 32 S1.1 Astronomical Time Periods 85 2.3 The Moon, Our Constant Companion 39 S1.2 Celestial Coordinates and Motion in the Sky 91 2.4 The Ancient Mystery of the Planets 46 S1.3 Principles of Celestial Navigation 101 Exercises and Problems 50 Exercises and Problems 106 Mathematical Insight 2.1: Angular Size, Physical Size, and Distance 28 Mathematical Insight S1.1: The Copernican Layout of the Solar System 88 Common Misconceptions: The Moon Illusion 29 Special Topic: Solar Days and the Analemma 92 Common Misconceptions: Stars in the Daytime 30 Mathematical Insight S1.2: Time by the Stars 96 Common Misconceptions: What Makes the North Star Special? 32 Common Misconceptions: Compass Directions 102 Common Misconceptions: The Cause of Seasons 33 Cosmic Context Part I: Our Expanding Perspective 108

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A01_BENN9068_08_NASTA_FM.indd 7 02/03/17 9:34 AM 6 telescoPES: PORTALS OF DISCOVERY 165 PART II 6.1 Eyes and Cameras: Everyday Light Sensors 166 Key Concepts for Astronomy 6.2 Telescopes: Giant Eyes 168 6.3 Telescopes and the Atmosphere 175 4 MAKING SENSE OF THE UNIVERSE: 6.4 Telescopes Across the Spectrum 179 UNDERSTANDING MOTION, ENERGY, AND GRAVITY 110 Exercises and Problems 185 4.1 Describing Motion: Examples from Daily Life 111 Common Misconceptions: Magnification and Telescopes 169 4.2 newton’s Laws of Motion 114 Mathematical Insight 6.1: Angular Resolution 170 4.3 Conservation Laws in Astronomy 117 Mathematical Insight 6.2: The Diffraction Limit 171 4.4 The Universal Law of Gravitation 123 Common Misconceptions: Twinkle, Twinkle, Little 4.5 orbits, Tides, and the Acceleration of Gravity 125 Star 176 Exercises and Problems 134 Common Misconceptions: Closer to the Stars? 177 Special Topic: Would You Like Your Own Telescope? 177 Common Misconceptions: No Gravity in Space? 114 Cosmic Context Part II: The Universality of Mathematical Insight 4.1: Units of Force, Physics 188 Mass, and Weight 116 Common Misconceptions: What Makes a Rocket Launch? 117 PART III Mathematical Insight 4.2: Mass-Energy 122 Mathematical Insight 4.3: Newton’s Version Learning from Other Worlds of Kepler’s Third Law 126 Mathematical Insight 4.4: Escape Velocity 128 7 our PLANETARY SYSTEM 190 Common Misconceptions: The Origin of Tides 128 7.1 Studying the Solar System 191 Mathematical Insight 4.5: The Acceleration of Gravity 131 7.2 Patterns in the Solar System 205 7.3 Spacecraft Exploration of the Solar System 207 5 light AND MATTER: Exercises and Problems 212 READING MESSAGES FROM THE COSMOS 137 Cosmic Context Figure 7.1: The Solar System 192 Special Topic: How Did We Learn the Scale of the Solar 5.1 Light in Everyday Life 138 System? 207 5.2 Properties of Light 139 5.3 Properties of Matter 143 8 forMATION OF THE SOLAR SYSTEM 214 5.4 Learning from Light 150 8.1 The Search for Origins 215 Exercises and Problems 162 8.2 Explaining the Major Features of the Solar Common Misconceptions: Is Radiation System 217 Dangerous? 142 8.3 The Age of the Solar System 225 Common Misconceptions: Can You Hear Exercises and Problems 230 Radio Waves or See an X Ray? 142 Mathematical Insight 5.1: Wavelength, Common Misconceptions: Solar Gravity and the Density Frequency, and Energy 144 of Planets 220 Special Topic: What Do Polarized Sunglasses Extraordinary Claims: A Giant Impact Made Our Moon 225 Have to Do with Astronomy? 145 Mathematical Insight 8.1: Radiometric Dating 227 Common Misconceptions: The Illusion Special Topic: What Started the Collapse of the Solar of Solidity 146 Nebula? 228 Common Misconceptions: One Phase at a Time? 147 9 PLANETARY GEOLOGY: EARTH AND Extraordinary Claims: We Can Never Learn the THE OTHER TERRESTRIAL WORLDS 233 Composition of Stars 154 Mathematical Insight 5.2: Laws of Thermal 9.1 Connecting Planetary Interiors and Surfaces 234 Radiation 155 9.2 Shaping Planetary Surfaces 240 Cosmic Context Figure 5.25: Interpreting a 9.3 Geology of the Moon and Mercury 248 Spectrum 158 9.4 Geology of Mars 251 Mathematical Insight 5.3: The Doppler Shift 160 9.5 Geology of Venus 257 9.6 The Unique Geology of Earth 259 Exercises and Problems 267

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A01_BENN9068_08_NASTA_FM.indd 8 02/03/17 9:34 AM Common Misconceptions: Earth Is Not Full of Molten Common Misconceptions: Dodge Those Lava 236 Asteroids! 351 Special Topic: How Do We Know What’s Inside Extraordinary Claims: The Death of the Dinosaurs Was Earth? 237 Catastrophic, Not Gradual 363 Common Misconceptions: Pressure and Temperature 238 13 other PLANETARY SYSTEMS: Mathematical Insight 9.1: The Surface THE NEW SCIENCE OF Area–to–Volume Ratio 239 DISTANT WORLDS 370 Extraordinary Claims: Martians! 252 13.1 Detecting Planets Around Other Stars 371 13.2 The Nature of Planets Around Other Stars 377 10 PLANETARY ATMOSPHERES: EARTH AND THE OTHER 13.3 The Formation of Other Solar Systems 390 TERRESTRIAL WORLDS 270 13.4 The Future of Extrasolar Planetary Science 392 10.1 Atmospheric Basics 271 Exercises and Problems 395

10.2 Weather and Climate 280 Special Topic: How Did We Learn That Other Stars Are 10.3 Atmospheres of the Moon and Mercury 286 Suns? 372 10.4 The Atmospheric History of Mars 288 Special Topic: The Names of Extrasolar Planets 376 10.5 The Atmospheric History of Venus 292 Cosmic Context Figure 13.6: Detecting Extrasolar Planets 378 10.6 Earth’s Unique Atmosphere 295 Mathematical Insight 13.1: Finding Orbital Distances for Exercises and Problems 307 Extrasolar Planets 380 Mathematical Insight 13.2: Finding Masses of Mathematical Insight 10.1: “No Greenhouse” Extrasolar Planets 382 Temperatures 275 Mathematical Insight 13.3: Finding Sizes of Extrasolar Common Misconceptions: Temperatures at Planets 386 High Altitude 277 Cosmic Context Part III: Learning from Other Common Misconceptions: Why Is the Sky Blue? 278 Worlds 398 Common Misconceptions: Toilets in the Southern Hemisphere 281 Special Topic: Weather and Chaos 283 PART IV Mathematical Insight 10.2: Thermal Escape from an Atmosphere 287 A Deeper Look at Nature Common Misconceptions: Ozone—Good or Bad? 296 Common Misconceptions: The Greenhouse Effect 299 S2 sPAce AND TIME 400 Cosmic Context Figure 10.42: Global Warming 302 S2.1 Einstein’s Revolution 401 Extraordinary Claims: Human Activity Can Change the S2.2 Relative Motion 404 Climate 304 S2.3 The Reality of Space and Time 408 11 JOVIAN PLANET SYSTEMS 310 S2.4 Toward a New Common Sense 416 11.1 A Different Kind of Planet 311 Exercises and Problems 419 11.2 A Wealth of Worlds: Satellites of Ice and Rock 322 Special Topic: What If Light Can’t Catch You? 407 11.3 Jovian Planet Rings 332 Mathematical Insight S2.1: The Time Dilation Formula 410 Exercises and Problems 338 Mathematical Insight S2.2: Formulas of Special Topic: How Were Uranus, Neptune, and Pluto Special Relativity 413 Discovered? 314 Special Topic: Measuring the Speed of Light 414 Mathematical Insight S2.3: Deriving E = mc2 415 12 asteroiDS, COMETS, AND DWARF PLANETS: THEIR NATURE, ORBITS, S3 sPAcetiME AND GRAVITY 422 AND IMPACTS 341 S3.1 Einstein’s Second Revolution 423 12.1 Classifying Small Bodies 342 S3.2 Understanding Spacetime 426 12.2 Asteroids 346 S3.3 A New View of Gravity 431 12.3 Comets 351 S3.4 Testing General Relativity 435 12.4 Pluto and the Kuiper Belt 356 S3.5 Hyperspace, Wormholes, and Warp Drive 438 12.5 Cosmic Collisions: Small Bodies versus the Planets 360 S3.6 The Last Word 440 Exercises and Problems 367 Exercises and Problems 442 Special Topic: Einstein’s Leap 425

Detailed Contents ix

A01_BENN9068_08_NASTA_FM.indd 9 02/03/17 9:34 AM Mathematical Insight S3.1: Spacetime Geometry 426 16.3 Masses of Newborn Stars 526 Special Topic: The Twin Paradox 439 Exercises and Problems 530

Mathematical Insight 16.1: Gravity versus Pressure 519 S4 BUILDING BLOCKS OF THE UNIVERSE 445

S4.1 The Quantum Revolution 446 17 star STUFF 534 S4.2 Fundamental Particles and Forces 446 17.1 Lives in the Balance 535 S4.3 Uncertainty and Exclusion in the 17.2 Life as a Low-Mass Star 536 Quantum Realm 451 17.3 Life as a High-Mass Star 542 S4.4 Key Quantum Effects in Astronomy 456 17.4 The Roles of Mass and Mass Exchange 549 Exercises and Problems 461 Exercises and Problems 554 Extraordinary Claims: Faster-Than-Light Neutrinos 450 Special Topic: How Long Is 5 Billion Years? 543 Special Topic: A String Theory of Everything? 452 Cosmic Context Figure 17.19: Summary of Stellar Special Topic: Does God Play Dice? 454 Lives 550 Mathematical Insight S4.1: Electron Waves in Atoms 455 18 the BIZARRE STELLAR GRAVEYARD 557 Cosmic Context Part IV: A Deeper Look at Nature 464 18.1 White Dwarfs 558 18.2 neutron Stars 561 18.3 Black Holes: Gravity’s Ultimate Victory 565 PART V 18.4 Extreme Events 570 Stars Exercises and Problems 574

Mathematical Insight 18.1: The Schwarzschild 14 our STAR 466 Radius 567 14.1 A Closer Look at the Sun 467 Common Misconceptions: Black Holes Don’t Suck 568 14.2 nuclear Fusion in the Sun 470 Extraordinary Claims: Neutron Stars and Black Holes Are Real 569 14.3 The Sun-Earth Connection 478 Cosmic Context Part V: Balancing Exercises and Problems 485 Pressure and Gravity 578

Common Misconceptions : The Sun Is Not on Fire 470 Mathematical Insight 14.1: Mass-Energy Conversion in Hydrogen Fusion 473 PART VI Mathematical Insight 14.2: Pressure in the Sun: The Galaxies and Beyond Ideal Gas Law 476

19 our GALAXY 580 15 surVEYING THE STARS 488 19.1 The Milky Way Revealed 581 15.1 Properties of Stars 489 19.2 Galactic Recycling 585 15.2 Patterns Among Stars 498 19.3 The History of the Milky Way 594 15.3 Star Clusters 506 19.4 The Galactic Center 596 Exercises and Problems 510 Exercises and Problems 601 Mathematical Insight 15.1: The Inverse Square Law for Light 490 Common Misconceptions: The Halo of a Galaxy 582 Mathematical Insight 15.2: The Parallax Formula 492 Special Topic: How Did We Learn the Structure of the Mathematical Insight 15.3: The Modern Magnitude Milky Way? 582 System 493 Special Topic: How Do We Determine Stellar Orbits? 583 Common Misconceptions: Photos of Stars 494 Mathematical Insight 19.1: Using Stellar Orbits to Mathematical Insight 15.4: Measuring Stellar Measure Galactic Mass 584 Masses 498 Common Misconceptions: The Sound of Space 587 Mathematical Insight 15.5: Calculating Stellar Common Misconceptions: What Is a Nebula? 593 Radii 499 Cosmic Context Figure 19.22: The Galactic Center 598 Cosmic Context Figure 15.10: Reading an H-R Diagram 500 20 galaXIES AND THE FOUNDATION OF MODERN COSMOLOGY 604 16 star BIRTH 513 20.1 islands of Stars 605 16.1 Stellar Nurseries 514 20.2 Measuring Galactic Distances 610 16.2 Stages of Star Birth 522 20.3 The Age of the Universe 617

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A01_BENN9068_08_NASTA_FM.indd 10 02/03/17 9:34 AM Exercises and Problems 624 Special Topic: Einstein’s Greatest Blunder 686 Mathematical Insight 20.1: Standard Candles 611 Cosmic Context Figure 23.20: Dark Matter and Dark Energy 688 Special Topic: Who Discovered the Expanding Universe? 615 Cosmic Context Part VI: Galaxy Evolution 696 Mathematical Insight 20.2: Redshift 616 Mathematical Insight 20.3: Understanding Hubble’s Law 618 PART VII Common Misconceptions: What Is the Universe Life on Earth and Beyond Expanding Into? 619 Mathematical Insight 20.4: Age from Hubble’s Constant 620 24 life IN THE UNIVERSE 698 Mathematical Insight 20.5: Cosmological Redshift and 24.1 Life on Earth 699 the Stretching of Light 621 24.2 Life in the Solar System 708 Common Misconceptions: Beyond the Horizon 622 24.3 Life Around Other Stars 711

21 galaXY EVOLUTION 627 24.4 The Search for Extraterrestrial Intelligence 715 24.5 interstellar Travel and Its Implications for 21.1 Looking Back Through Time 628 Civilization 718 21.2 The Lives of Galaxies 630 Exercises and Problems 723 21.3 The Role of Supermassive Black Holes 636 21.4 Gas Beyond the Stars 641 Special Topic: Evolution and the Schools 707 Special Topic: What Is Life? 708 Exercises and Problems 644 Extraordinary Claims: Aliens Are Visiting Mathematical Insight 21.1: Feeding a Black Hole 638 Earth in UFOs 717 Mathematical Insight 21.2: Weighing Supermassive Cosmic Context Part VII: A Universe of Life? 726 Black Holes 642 CREDITS C-1 22 the BIRTH OF THE UNIVERSE 648 22.1 The Big Bang Theory 649 APPENDIXES A-1 22.2 Evidence for the Big Bang 653 A Useful Numbers A-2 22.3 The Big Bang and Inflation 659 B Useful Formulas A-3 22.4 observing the Big Bang for Yourself 663 C A Few Mathematical Skills A-4 Exercises and Problems 666 D The Periodic Table of the Elements A-10 Cosmic Context Figure 22.5: The Early Universe 654 E Planetary Data A-11 Extraordinary Claims: The Universe Doesn’t Change with F Stellar Data A-14 Time 657 G Galaxy Data A-16 Mathematical Insight 22.1: Temperature and Wavelength of Background Radiation 658 H The 88 Constellations A-19 I Star Charts A-21 23 DARK MATTER, DARK ENERGY, J Key to Icons on Figures A-26 AND THE FATE OF THE UNIVERSE 669 23.1 Unseen Influences in the Cosmos 670 GLOSSARY A-1 23.2 Evidence for Dark Matter 671 23.3 Structure Formation 680 INDEX I-1 23.4 Dark Energy and the Fate of the Universe 683 Exercises and Problems 692

Mathematical Insight 23.1: Mass-to-Light Ratio 673 Mathematical Insight 23.2: Finding Cluster Masses from Galaxy Orbits 675 Mathematical Insight 23.3: Finding Cluster Masses from Gas Temperature 677 Extraordinary Claims: Most of the Universe’s Matter Is Dark 678

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A01_BENN9068_08_NASTA_FM.indd 11 02/03/17 9:34 AM Preface

We humans have gazed into the sky for countless gen- edition. The full list is too long to put here, but erations. We have wondered how our lives are connected major changes include the following: to the Sun, Moon, planets, and stars that adorn the heav- ■ In Chapter 2, we have made a number of small ens. Today, through the science of astronomy, we know changes to make sure the discussion works for that these connections go far deeper than our ancestors students in the Southern Hemisphere in addition ever imagined. This book tells the story of modern as- to working for those in the Northern Hemisphere. tronomy and the new perspective, The Cosmic Perspec- ■ In Chapter 3, we have enhanced the discussion of tive, that astronomy gives us of ourselves and our planet. the nature of science with the new Table 3.2, which This book grew out of our experience teaching as- summarizes how the same terms often have different tronomy to both college students and the general public meanings in science than in everyday usage. over more than 30 years. During this time, a flood of new ■ Chapters 9 and 10 have been significantly discoveries fueled a revolution in our understanding of rewritten to reflect new results from MESSENGER the cosmos but had little impact on the basic organiza- at Mercury, Curiosity and MAVEN at Mars, and tion and approach of most astronomy textbooks. We felt the latest data on global warming. the time had come to rethink how to organize and teach ■ Chapter 12 has been significantly reorganized and the major concepts in astronomy to reflect this revolu- rewritten to reflect recent developments in the tion in scientific understanding. This book is the result. study of small bodies, particularly the revolutionary new views provided by recent spacecraft including Who Is This Book For? Dawn, Rosetta, and New Horizons. The Cosmic Perspective is designed as a textbook for col- ■ Chapter 13 has been heavily revised in light lege courses in introductory astronomy, but is suitable of thousands of new discoveries of extrasolar for anyone who is curious about the universe. We as- planets since the prior edition. sume no prior knowledge of astronomy or physics, and ■ In Chapter 14, we have updated the discussion of the book is especially suited to students who do not in- solar neutrinos and reorganized Section 14.3 into tend to major in mathematics or science. two (rather than the former three) learning goals. The Cosmic Perspective provides a comprehensive ■ In Chapter 18, we have almost completely survey of modern astronomy, and it contains enough rewritten Section 18.4 to focus on events in which material for a two-semester introductory astronomy black holes can form and neutron stars merge. sequence. It may also be used for one-semester survey ■ Chapter 19 has been revised to reduce jargon and courses if professors choose their areas of emphasis. to include a new full-page figure showing the Milky However, instructors of one-term courses may also wish Way in different wavelengths. In addition, Section to consider our two shorter versions of this book: The 19.4 on the galactic center has been rewritten and Essential Cosmic Perspective, which covers a smaller set features a new two-page Cosmic Context spread. of topics and is tailored to meet the needs of comprehen- ■ Chapters 20 and 21 have been significantly revised sive one-semester survey courses in astronomy, and The in light of new research into galactic evolution, Cosmic Perspective Fundamentals, which covers only the some of which is based on the work of two of the most fundamental topics in astronomy and is designed authors of this book (Donahue and Voit). for courses that address a more limited set of topics. ■ Chapter 23 has been updated to reflect the latest results about dark energy and the expansion of N ew to This Edition the universe. ■ Chapter 24 has been significantly rewritten, The underlying philosophy, goals, and structure of particularly Sections 24.2 and 24.3 (which has The Cosmic Perspective remain the same as in past edi- also been completely reorganized), thanks to tions, but we have thoroughly updated the text and new understanding of the potential habitability of made a number of other improvements. Here, briefly, Mars, Titan, and extrasolar planets. is a list of the significant changes you’ll find in the ■ Fully Updated Science: Astronomy is a fast-moving eighth edition: field, and numerous new developments have ■ Major Chapter-Level Changes: We have made occurred since the prior edition was published. numerous significant changes to both update the In addition to the major chapter-level changes science and improve the pedagogical flow in this above, other scientific updates in this edition include

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A01_BENN9068_08_NASTA_FM.indd 12 02/03/17 9:34 AM ■ New results and images from spacecraft exploring taken any formal science courses and who may begin the our solar system, including Curiosity and MAVEN course with little understanding of how science works. We at Mars, Cassini at Saturn, MESSENGER at Mercury, built our book around the following five key themes: Dawn at Ceres, New Horizons at Pluto, and more ■ Theme 1: We are a part of the universe and thus can ■ Recent results from major space observatories, learn about our origins by studying the universe. This including Hubble and Kepler, and from powerful is the overarching theme of The Cosmic Perspective, ground-based observatories such as ALMA as we continually emphasize that learning about the ■ Updated data and models on topics including the universe helps us understand ourselves. Studying formation of planetary systems, global warming, the intimate connections between human life and and galaxy formation and evolution the cosmos gives students a reason to care about ■ Major new discoveries and statistics relating to astronomy and also deepens their appreciation of the the study of extrasolar planets, new research on unique and fragile nature of our planet and its life. the timing and possible origin of life on Earth, ■ Theme 2: The universe is comprehensible through and much more scientific principles that anyone can understand. ■ New Feature — Extraordinary Claims boxes: Carl The universe is comprehensible because the same Sagan made famous the statement “extraordinary claims physical laws appear to be at work in every aspect, require extraordinary evidence.” With this new feature, on every scale, and in every age of the universe. we provide students with examples of extraordinary Moreover, while professional scientists generally have claims about the universe and how they were either discovered the laws, anyone can understand their supported or debunked as scientists collected more fundamental features. Students can learn enough in evidence. The first of these features appears in one or two terms of astronomy to comprehend the Chapter 3, where the context of Sagan’s dictum is also basic reasons for many phenomena that they see explained. Another nine Extraordinary Claims boxes are around them—phenomena ranging from seasonal sprinkled throughout the rest of the text. changes and phases of the Moon to the most esoteric ■ New Content in MasteringAstronomy®: The Cosmic astronomical images that appear in the news. Perspective is no longer just a textbook; rather, it ■ Theme 3: Science is not a body of facts but rather is a “learning package” that combines a printed a process through which we seek to understand the book with deeply integrated, interactive media world around us. Many students assume that science developed to support every chapter of our book. is just a laundry list of facts. The long history of For students, the MasteringAstronomy Study Area astronomy can show them that science is a process provides a wealth of tutorials and activities to build through which we learn about our universe—a understanding, while quizzes and exercises allow process that is not always a straight line to the truth. them to test what they’ve learned. For instructors, That is why our ideas about the cosmos sometimes the MasteringAstronomy Item Library provides the change as we learn more, as they did dramatically unprecedented ability to quickly build, post, and when we first recognized that Earth is a planet going automatically grade pre- and post-lecture diagnostic around the Sun rather than the center of the universe. tests, weekly homework assignments, and exams In this book, we continually emphasize the nature of appropriate difficulty, duration, and content of science so that students can understand how and coverage. It also provides the ability to record why modern theories have gained acceptance and detailed information on the step-by-step work of why these theories may still change in the future. every student directly into a powerful and easy- ■ Theme 4: A course in astronomy is the beginning of a to-use gradebook, and to evaluate results with a lifelong learning experience. Building upon the prior sophisticated suite of diagnostics. Among the changes themes, we emphasize that what students learn in you’ll find to the MasteringAstronomy site for this their astronomy course is not an end but a beginning. edition are numerous new and revised interactive By remembering a few key physical principles and figures, including many narrated video tours; understanding the nature of science, students can numerous new tutorials in the Item Library; and follow astronomical developments for the rest of their a fully updated set of reading, concept, and visual lives. We therefore seek to motivate students enough quizzes in both the Study Area and the Item Library. that they will continue to participate in the ongoing human adventure of astronomical discovery. ■ Theme 5: Astronomy affects each of us personally T hemes of The Cosmic Perspective with the new perspectives it offers. We all conduct The Cosmic Perspective offers a broad survey of modern un- the daily business of our lives with reference to derstanding of the cosmos and of how we have built that some “world view”—a set of personal beliefs about understanding. Such a survey can be presented in a number our place and purpose in the universe that we have of different ways. We have chosen to interweave a few key developed through a combination of schooling, themes throughout the book, each selected to help make religious training, and personal thought. This world the subject more appealing to students who may never have view shapes our beliefs and many of our actions.

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A01_BENN9068_08_NASTA_FM.indd 13 02/03/17 9:34 AM Although astronomy does not mandate a particular momentum (introduced in Section 4.3) reappear set of beliefs, it does provide perspectives on the throughout the book, and we find that the wide architecture of the universe that can influence variety of features found on the terrestrial planets can how we view ourselves and our world, and these be understood through just a few basic geological perspectives can potentially affect our behavior. For processes. Research shows that, long after the course example, someone who believes Earth to be at the is over, students are far more likely to retain such center of the universe might treat our planet quite conceptual learning than individual facts or details. differently from someone who views it as a tiny and ■ Proceed from the more familiar and concrete to the fragile world in the vast cosmos. In many respects, less familiar and abstract. It’s well known that the role of astronomy in shaping world views may children learn best by starting with concrete ideas be to represent the deepest connection between the and then generalizing to abstractions later. The same universe and the everyday lives of humans. is true for many adults. We therefore always try to “build bridges to the familiar”— that is, to begin Pedagogical Principles of with concrete or familiar ideas and then gradually The Cosmic Perspective draw more general principles from them. ■ Use plain language. Surveys have found that the No matter how an astronomy course is taught, it is very number of new terms in many introductory astronomy important to present material according to a clear set of books is larger than the number of words taught in pedagogical principles. The following list briefly sum- many first-year courses on a foreign language. In marizes the major pedagogical principles that we apply essence, this means the books are teaching astronomy throughout this book. (The Instructor Guide describes in what looks to students like a foreign language! these principles in more detail.) Clearly, it is much easier for students to understand ■ Stay focused on the big picture. Astronomy is filled key astronomical concepts if they are explained in with interesting facts and details, but they are plain English without resorting to unnecessary jargon. meaningless unless they fit into a big picture view of We have gone to great lengths to eliminate jargon as the universe. We therefore take care to stay focused much as possible or, at minimum, to replace standard on the big picture (essentially the themes discussed jargon with terms that are easier to remember in the above) at all times. A major benefit of this approach context of the subject matter. is that although students may forget individual facts ■ Recognize and address student misconceptions. and details after the course is over, the big picture Students do not arrive as blank slates. Most students framework should stay with them for life. enter our courses not only lacking the knowledge we ■ Always provide context first. We all learn new hope to teach but often holding misconceptions about material more easily when we understand why we astronomical ideas. Therefore, to teach correct ideas, are learning it. In essence, this is simply the idea that we must also help students recognize the paradoxes it is easier to get somewhere when you know where in their prior misconceptions. We address this issue you are going. We therefore begin the book (Chapter in a number of ways, the most obvious being the 1) with a broad overview of modern understanding presence of many Common Misconceptions boxes. of the cosmos, so that students can know what they These summarize commonly held misconceptions will be studying in the rest of the book. We maintain and explain why they cannot be correct. this “context first” approach throughout the book by always telling students what they will be learning, and why, before diving into the details. T he Topical (Part) Structure of ■ Make the material relevant. It’s human nature to be The Cosmic Perspective more interested in subjects that seem relevant to our The Cosmic Perspective is organized into seven broad topi- lives. Fortunately, astronomy is filled with ideas that cal areas (the seven Parts in the table of contents), each ap- touch each of us personally. For example, the study proached in a distinctive way designed to help maintain the of our solar system helps us better understand and focus on the themes discussed earlier. Here, we summarize appreciate our planet Earth, and the study of stars and the guiding philosophy through which we have approached galaxies helps us learn how we have come to exist. By each topic. Every Part concludes with one of our two-page emphasizing our personal connections to the cosmos, Cosmic Context spreads, which tie together into a coherent we make the material more meaningful, inspiring whole the diverse ideas covered in the individual chapters. students to put in the effort necessary to learn it. ■ Emphasize conceptual understanding over “stamp collecting” of facts. If we are not careful, astronomy Part I: Developing Perspective can appear to be an overwhelming collection of facts (Chapters 1–3, S1) that are easily forgotten when the course ends. We Guiding Philosophy: Introduce the big picture, the process therefore emphasize a few key conceptual ideas that of science, and the historical context of astronomy. we use over and over again. For example, the laws of The basic goal of these chapters is to give students a conservation of energy and conservation of angular big picture overview and context for the rest of the book, xiv Preface

A01_BENN9068_08_NASTA_FM.indd 14 02/03/17 9:34 AM and to help them develop an appreciation for the pro- the terrestrial planets, covering key ideas of geology and cess of science and how science has developed through atmospheres, respectively. In both chapters, we start with history. Chapter 1 outlines our modern understanding examples from our own planet Earth to help students un- of the cosmos, including the scale of space and time, derstand the types of features that are found throughout so that students gain perspective on the entire universe the terrestrial worlds and the fundamental processes that before diving into its details. Chapter 2 introduces basic explain how these features came to be. We then complete sky phenomena, including seasons and phases of the each of these chapters by summarizing how the vari- Moon, and provides perspective on how phenomena we ous processes have played out on each individual world. experience every day are tied to the broader cosmos. Chapter 11 covers the jovian planets and their moons and Chapter 3 discusses the nature of science, offering a his- rings. Chapter 12 covers small bodies in the solar system, torical perspective on the development of science and including asteroids, comets, and dwarf planets. It also cov- giving students perspective on how science works and ers cosmic collisions, including the impact linked to the how it differs from nonscience. The supplementary (op- extinction of the dinosaurs and a discussion of how seri- tional) Chapter S1 goes into more detail about the sky, ously we should take the ongoing impact threat. Finally, including celestial timekeeping and navigation. Chapter 13 turns to the exciting topic of other planetary The Cosmic Context figure for Part I appears on systems that have been discovered in recent years. Note pp. 108–109. that Parts III is essentially independent of Parts IV through VII, and can be covered either before or after them. Part II: Key Concepts for The Cosmic Context figure for Part III appears on Astronomy (Chapters 4–6) pp. 398–399. Guiding Philosophy: Connect the physics of the cosmos to everyday experiences. Part IV: A Deeper Look at Nature These chapters lay the groundwork for understanding (Chapters S2–S4) astronomy through what is sometimes called the “uni- Guiding Philosophy: Ideas of relativity and quantum versality of physics”—the idea that a few key principles mechanics are accessible to anyone. governing matter, energy, light, and motion explain both Nearly all students have at least heard of things like the phenomena of our daily lives and the mysteries of the the prohibition on faster-than-light travel, curvature of cosmos. Each chapter begins with a section on science in spacetime, and the uncertainty principle. But few (if any) everyday life in which we remind students how much they students enter an introductory astronomy course with any already know about scientific phenomena from their ev- idea of what these things mean, and they are naturally eryday experiences. We then build on this everyday knowl- curious about them. Moreover, a basic understanding of edge to help students learn the formal principles of physics the ideas of relativity and quantum mechanics makes it needed for the rest of their study of astronomy. Chapter 4 possible to gain a much deeper appreciation of many of covers the laws of motion, the crucial conservation laws of the most important and interesting topics in modern as- angular momentum and energy, and the universal law of tronomy including black holes, gravitational lensing, and gravitation. Chapter 5 covers the nature of light and matter, the overall geometry of the universe. The three chapters of the formation of spectra, and the Doppler effect. Chapter 6 Part IV cover special relativity (Chapter S2), general rela- covers telescopes and astronomical observing techniques. tivity (Chapter S3), and key astronomical ideas of quan- The Cosmic Context figure for Part II appears on tum mechanics (Chapter S4). The main thrust throughout pp. 188–189. is to demystify relativity and quantum mechanics by con- vincing students that they are capable of understanding Part III: Learning from Other the key ideas despite the reputation of these subjects for Worlds (Chapters 7–13) being hard or counterintuitive. These chapters are labeled “supplementary” because coverage of them is optional. Guiding Philosophy: We learn about our own world and Covering them will give your students a deeper under- existence by studying about other planets in our solar standing of the topics that follow on stars, galaxies, and system and beyond. cosmology, but the later chapters are self-contained so that This set of chapters begins in Chapter 7 with a broad they may be covered without having covered Part IV at all. overview of the solar system, including an 11-page tour The Cosmic Context figure for Part IV appears on that highlights some of the most important and interesting pp. 464–465. features of the Sun and each of the planets in our solar system. In the remaining chapters of this Part, we seek to explain these features through a true comparative Part V: Stars (Chapters 14–18) planetology approach, in which the discussion empha- Guiding Philosophy: We are intimately connected to the sizes the processes that shape the planets rather than the stars. “stamp collecting” of facts about them. Chapter 8 uses the These are our chapters on stars and stellar life cycles. concrete features of the solar system presented in Chapter 7 Chapter 14 covers the Sun in depth so that it can serve as to build student understanding of the current theory a concrete model for building an understanding of oth- of solar system formation. Chapters 9 and 10 focus on er stars. Chapter 15 describes the general properties of Preface xv

A01_BENN9068_08_NASTA_FM.indd 15 02/03/17 9:34 AM other stars, how we measure these properties, and how on these key goals as they work through the we classify stars with the H-R diagram. Chapter 16 cov- chapter. ers star birth, and the rest of stellar evolution is discussed ■ Introduction and Epigraph: The main chapter in Chapter 17. Chapter 18 covers the end points of stellar text begins with a one- to three-paragraph evolution: white dwarfs, neutron stars, and black holes. introduction to the chapter material and an The Cosmic Context figure for Part V appears on inspirational quotation relevant to the chapter. pp. 578–579. ■ Section Structure: Chapters are divided into numbered sections, each addressing one key aspect Part VI: Galaxies and Beyond of the chapter material. Each section begins with a (Chapters 19–23) short introduction that leads into a set of learning goals relevant to the section—the same learning Guiding Philosophy: Present galaxy evolution and cos- goals listed at the beginning of the chapter. mology together as intimately related topics. ■ The Big Picture: Every chapter narrative ends These chapters cover galaxies and cosmology. Chapter with this feature, designed to help students put 19 presents the Milky Way as a paradigm for galaxies in what they’ve learned in the chapter into the much the same way that Chapter 14 uses the Sun as a para- context of the overall goal of gaining a broader digm for stars. Chapter 20 presents the properties of galax- perspective on ourselves, our planet, and ies and shows how the quest to measure galactic distances prospects for life beyond Earth. led to Hubble’s law and laid the foundation for modern ■ Chapter Summary: The end-of-chapter summary cosmology. Chapter 21 discusses how the current state of offers a concise review of the learning goal knowledge regarding galaxy evolution has emerged from questions, helping reinforce student understanding our ability to look back through time. Chapter 22 then of key concepts from the chapter. Thumbnail presents the Big Bang theory and the evidence supporting figures are included to remind students of key it, setting the stage for Chapter 23, which explores dark illustrations and photos in the chapter. matter and its role in galaxy formation, as well as dark ■ End-of-Chapter Exercises: Each chapter includes an energy and its implications for the fate of the universe. extensive set of exercises that can be used for study, The Cosmic Context figure for Part VI appears on discussion, or assignment. All of the end-of-chapter pp. 696–697. exercises are organized into the following subsets: ■ Visual Skills Check: A set of questions designed PartI VI : Life on Earth and to help students build their skills at interpret- Beyond (Chapter 24) ing the many types of visual information used in Guiding Philosophy: The study of life on Earth helps us astronomy understand the search for life in the universe. ■ Review Questions: Questions that students This Part consists of a single chapter. It may be considered should be able to answer from the reading alone optional, to be used as time allows. Those who wish to teach ■ Does It Make Sense? (or similar title): A set of short a more detailed course on astrobiology may wish to consider statements that students are expected to evaluate, the text Life in the Universe, by Bennett and Shostak. determining whether each statement makes sense The Cosmic Context figure for Part VII appears on and explaining why or why not. These exercises are pp. 726–727. generally easy once students understand a particular concept, but very difficult otherwise; thus, they are Pedagogical Features of an excellent probe of comprehension. The Cosmic Perspective ■ Quick Quiz: A short multiple-choice quiz that allows students to check their progress Along with the main narrative, The Cosmic Perspective ■ Process of Science Questions: Essay or includes a number of pedagogical devices designed to discussion questions that help students focus on enhance student learning: how science progresses over time ■ Basic Chapter Structure: Each chapter is carefully ■ Group Work Exercise: A suggested activity structured to ensure that students understand the designed for collaborative learning in class goals up front, learn the details, and pull together all ■ Short-Answer/Essay Questions: Questions that the ideas at the end. In particular, note the following go beyond the Review Questions in asking for key structural elements: conceptual interpretation ■ Chapter Learning Goals: Each chapter opens ■ Quantitative Problems: Problems that require with a page offering an enticing image and a brief some mathematics, usually based on topics overview of the chapter, including a list of the covered in the Mathematical Insight boxes section titles and associated learning goals. The ■ Discussion Questions: Open-ended questions for learning goals are presented as key questions de- class discussions signed to help students both to understand what ■ Web Projects: A few suggestions for additional they will be learning about and to stay focused web-based research

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A01_BENN9068_08_NASTA_FM.indd 16 02/03/17 9:34 AM ■ Additional Features: You’ll find a number of other ■ Cross-References: When a concept is covered in features designed to increase student understanding, greater detail elsewhere in the book, we include a both within individual chapters and at the end of cross-reference in brackets to the relevant section the book, including the following: (e.g., [Section 5.2]). ■ Annotated Figures: Key figures in each chapter ■ Glossary: A detailed glossary makes it easy for use the research-proven technique of annotation— students to look up important terms. the placement on the figure of carefully crafted ■ Appendixes: The appendixes contain a number of text (in blue) to guide students through interpret- useful references and tables including key constants ing graphs, following process figures, and trans- (Appendix A), key formulas (Appendix B), key lating between different representations. mathematical skills (Appendix C), and numerous ■ Cosmic Context Two-Page Figures: These two- data tables and star charts (Appendixes D–I). page spreads provide visual summaries of key processes and concepts. MasteringAstronomy® ■ Wavelength/Observatory Icons: For What is the single most important factor in student success astronomical images, simple icons indicate in astronomy? Both research and common sense reveal the whether the image is a photo, artist’s impression, same answer: study time. No matter how good the teacher or computer simulation; whether a photo came or how good the textbook, students learn only when they from ground-based or space-based observations; spend adequate time studying. Unfortunately, limitations and the wavelength band used to take the photo. on resources for grading have prevented most instructors ■ MasteringAstronomy® Resources: Specific resources from assigning much homework despite its obvious ben- from the MasteringAstronomy site, such as Interactive efits to student learning. And limitations on help and of- Figures or Photos and Self-Guided Tutorials, are fice hours have made it difficult for students to make sure referenced alongside specific figure and section titles they use self-study time effectively. That, in a nutshell, to direct students to help when they need it. is why we created MasteringAstronomy. For students, it ■ Think About It: This feature, which appears provides adaptive learning designed to coach them indi- throughout the book in the form of short vidually—responding to their errors with specific, targeted questions integrated into the narrative, gives feedback and providing optional hints for those who need students the opportunity to reflect on important additional guidance. For professors, MasteringAstronomy new concepts. It also serves as an excellent provides unprecedented ability to automatically monitor starting point for classroom discussions. and record students’ step-by-step work and evaluate the ■ See It for Yourself: This feature also occurs effectiveness of assignments and exams. As a result, we throughout the book, integrated into the believe that MasteringAstronomy can change the way as- narrative; it gives students the opportunity to tronomy courses are taught: It is now possible, even in conduct simple observations or experiments that large classes, to ensure that each student spends his or her will help them understand key concepts. study time on optimal learning activities outside of class. ■ Common Misconceptions: These boxes address MasteringAstronomy provides students with a wealth popularly held but incorrect ideas related to the of self-study resources including interactive tutorials tar- chapter material. geting the most difficult concepts of the course, interactive ■ Special Topic Boxes: These boxes address and narrated versions of key figures and photos, self-study supplementary discussion topics related to the quizzes, and other activities for self-assessment covering chapter material but not prerequisite to the every chapter. For professors, MasteringAstronomy pro- continuing discussion. vides a library of tutoring activities that is periodically up- ■ Extraordinary Claims Boxes: Carl Sagan made dated based on the performance of students nationwide. famous the statement “extraordinary claims You can create assignments tailored to your specific class require extraordinary evidence.” These boxes goals from among hundreds of activities and problems provide students with examples of extraordinary including pre- and post-lecture diagnostic quizzes, tutor- claims about the universe and how they were ing activities, end-of-chapter problems from this textbook, either supported or debunked as scientists and test bank questions. MasteringAstronomy now also in- collected more evidence. cludes Learning Catalytics, which provides additional capa- ■ Mathematical Insight Boxes: These boxes bilities for in-class learning. Visit the MasteringAstronomy contain most of the mathematics used in the website to learn more. book and can be covered or skipped depending Finally, in a world where everyone claims to have the on the level of mathematics that you wish best website, we’d like to point out three reasons why to include in your course. The Mathematical you’ll discover that MasteringAstronomy really does Insights use a three-step problem-solving stand out from the crowd: strategy—Understand, Solve, and Explain—that gives students a consistent and explicit structure ■ MasteringAstronomy specifically supports the structure for solving quantitative homework problems. and pedagogy of The Cosmic Perspective. You’ll find

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A01_BENN9068_08_NASTA_FM.indd 17 02/03/17 9:34 AM the same concepts emphasized in the book and on up-to-date content and technology to customers. Customer will be the website, using the same terminology and the same notified of any change prior to the beginning of the new school year. pedagogical approaches. This type of consistency will ensure that students focus on the concepts, without the Instructor Resource’s risk of becoming confused by different presentations. Most of the teacher supplements and resources for this ■ Nearly all MasteringAstronomy content has been text are available electronically to qualified adopters developed either directly by The Cosmic Perspective within Mastering and on the Instructor Resource Center author team or by this author team in close (IRC). Upon adoption or to preview, please go to www collaboration with outstanding educators including .pearsonschool.com/access_request and select Instruc- Jim Dove, Jim Cooney, Jonathan Williams, Richard tor Resource Center. You will be required to complete a Gelderman, Lauren Jones, Ed Prather, Tim Slater, brief one-time registration subject to verification of edu- and Daniel Loranz. The direct involvement of The cator status. Upon verification, access information and Cosmic Perspective authors ensures that you can instructions will be sent to you via e-mail. Once logged expect the same high level of quality in our website into the IRC, enter 0-13-475266-X in the “Search our Cata- that you have come to expect in our textbook. log” box to locate resources. ■ The MasteringAstronomy platform uses the Contact your local Pearson Account General Manager same unique student-driven engine as the highly to find out more about the following supplements: successful MasteringPhysics® product (the most widely adopted physics homework and tutorial ■ Instructor Resource’s This comprehensive collection system), developed by a group led by MIT physicist of instructor resources includes high-resolution JPEGs David Pritchard. This robust platform gives of all images from the book; Interactive Figures and instructors unprecedented power not only to tailor Photos™ based on figures in the text; additional content to their own courses but also to evaluate the applets and animations to illustrate key concepts; effectiveness of assignments and exams. PowerPoint® Lecture Outlines that incorporate figures, photos, checkpoint questions, and multimedia; and Mastering Preview and Adoption Access PRS-enabled clicker quizzes based on the book and Upon textbook purchase, students and teachers are book-specific interactive media, to make preparing for granted access to MasteringBiology with Pearson eText. lectures quick and easy. These resources are located High school teachers can obtain preview or adoption ac- in MasteringAstronomy for easy use. cess to MasteringBiology in one of the following ways: ■ Clickers in the Astronomy Classroom This 100-page handbook by Douglas Duncan provides everything you Preview Access need to know to successfully introduce or enhance your use of CRS (clicker) quizzing in your astronomy class— ■ Teachers can request preview access online by the research-proven benefits, common pitfalls to avoid, visiting www.PearsonSchool.com/Access_Request. and a wealth of thought-provoking astronomy questions Select Science, choose Initial Access, and complete for every week of your course. These resources are the form under Option 2. Preview Access located in MasteringAstronomy for easy use. information will be sent to the teacher via e-mail. ■ Instructor Guide The Instructor Guide contains Adoption Access a detailed overview of the text, sample syllabi for courses of different emphasis and duration, ■ With the purchase of this program, a Pearson suggested teaching strategies, answers or discussion Adoption Access Card with Instructor Manual points for all Think About It and See It for Yourself will be delivered with your textbook purchase. questions in the text, solutions to all end-of- (ISBN: 978-0-13-354087-1) chapter problems, and a detailed reference guide ■ Ask your sales representative for a Pearson Adoption summarizing media resources available for every Access Card with Instructor Manual. chapter and section of the book. These resources are (ISBN: 978-0-13-354087-1) located in MasteringAstronomy for easy use. OR ■ Test Bank Available in both Word and TestGen formats on the Instructor Resource Center and ■ Visit PearsonSchool.com/Access_Request, select MasteringAstronomy, the Test Bank contains a broad Science, choose Initial Access, and complete the set of multiple-choice, true/false, and free-response form under Option 3—MyLab/Mastering Class questions for each chapter. The Test Bank is also Adoption Access. Teacher and Student access assignable through MasteringAstronomy. information will be sent to the teacher via e-mail. Acknowledgments Students, ask your teacher for access Pearson reserves the right to change and/or update technology plat- Our textbook carries only four author names, but in fact forms, including possible edition updates to customers during the it is the result of hard work by a long list of committed term of access. This will allow Pearson to continue to deliver the most individuals. We could not possibly list everyone who has

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A01_BENN9068_08_NASTA_FM.indd 18 02/03/17 5:55 PM helped, but we would like to call attention to a few peo- Peter Cottrell, University of Canterbury ple who have played particularly important roles. First, John Cowan, University of Oklahoma we thank our editors and friends at Pearson, who have Kevin Crosby, Carthage College stuck with us through thick and thin, including Adam Christopher Crow, Indiana University—Purdue Black, Nancy Whilton, Jim Smith, Michael Gillespie, University Fort Wayne Mary Ripley, Chandrika Madhavan, and Corinne Benson. Manfred Cuntz, University of Texas at Arlington Special thanks to our production teams, especially Sally Christopher De Vries, California State University, Lifland, and our art and design team. Stanislaus We’ve also been fortunate to have an outstanding group John M. Dickey, University of Minnesota of reviewers, whose extensive comments and suggestions Matthias Dietrich, Worcester State University helped us shape the book. We thank all those who have Bryan Dunne, University of Illinois, reviewed drafts of the book in various stages, including Urbana-Champaign Suzan Edwards, Smith College Marilyn Akins, Broome Community College Robert Egler, North Carolina State University at Christopher M. Anderson, University of Wisconsin Raleigh John Anderson, University of North Florida Paul Eskridge, Minnesota State University Peter S. Anderson, Oakland Community College David Falk, Los Angeles Valley College Keith Ashman Timothy Farris, Vanderbilt University Simon P. Balm, Santa Monica College Robert A. Fesen, Dartmouth College Reba Bandyopadhyay, University of Florida Tom Fleming, University of Arizona Nadine Barlow, Northern Arizona University Douglas Franklin, Western Illinois University John Beaver, University of Wisconsin at Fox Valley Sidney Freudenstein, Metropolitan State College of Peter A. Becker, George Mason University Denver Timothy C. Beers, National Optical Astronomy Martin Gaskell, University of Nebraska Observatory Richard Gelderman, Western Kentucky University Jim Bell, Arizona State University Harold A. Geller, George Mason University Priscilla J. Benson, Wellesley College Donna Gifford, Pima Community College Philip Blanco, Grossmont College Mitch Gillam, Marion L. Steele High School Jeff R. Bodart, Chipola College Bernard Gilroy, The Hun School of Princeton Bernard W. Bopp, University of Toledo Owen Gingerich, Harvard–Smithsonian Sukanta Bose, Washington State University (Historical Accuracy Reviewer) David Brain, University of Colorado David Graff, U.S. Merchant Marine Academy David Branch, University of Oklahoma Richard Gray, Appalachian State University John C. Brandt, University of New Mexico Kevin Grazier, Jet Propulsion Laboratory James E. Brau, University of Oregon Robert Greeney, Holyoke Community College Jean P. Brodie, UCO/Lick Observatory, University Henry Greenside, Duke University of California, Santa Cruz Alan Greer, Gonzaga University Erik Brogt, University of Canterbury John Griffith, Lin-Benton Community College James Brooks, Florida State University David Griffiths, Oregon State University Daniel Bruton, Stephen F. Austin State University David Grinspoon, Planetary Science Institute Debra Burris, University of Central Arkansas John Gris, University of Delaware Scott Calvin, Sarah Lawrence College Bruce Gronich, University of Texas at El Paso Amy Campbell, Louisiana State University Thomasana Hail, Parkland University Eugene R. Capriotti, Michigan State University Jim Hamm, Big Bend Community College Eric Carlson, Wake Forest University Charles Hartley, Hartwick College David A. Cebula, Pacific University J. Hasbun, University of West Georgia Supriya Chakrabarti, University of Massachusetts, Joe Heafner, Catawba Valley Community College Lowell David Herrick, Maysville Community College Kwang-Ping Cheng, California State University Scott Hildreth, Chabot College Fullerton Tracy Hodge, Berea College Dipak Chowdhury, Indiana University—Purdue Mark Hollabaugh, Normandale Community College University Fort Wayne Richard Holland, Southern Illinois University, Chris Churchill, New Mexico State University Carbondale Josh Colwell, University of Central Florida Joseph Howard, Salisbury University James Cooney, University of Central Florida James Christopher Hunt, Prince George’s Anita B. Corn, Colorado School of Mines Community College Philip E. Corn, Red Rocks Community College Richard Ignace, University of Wisconsin Kelli Corrado, Montgomery County Community College James Imamura, University of Oregon

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A01_BENN9068_08_NASTA_FM.indd 19 02/03/17 9:34 AM Douglas R. Ingram, Texas Christian University Charles Peterson, University of Missouri, Columbia Assad Istephan, Madonna University Cynthia W. Peterson, University of Connecticut Bruce Jakosky, University of Colorado Jorge Piekarewicz, Florida State University Adam G. Jensen, University of Colorado Lawrence Pinsky, University of Houston Adam Johnston, Weber State University Stephanie Plante, Grossmont College Lauren Jones, Gettysburg College Jascha Polet, California State Polytechnic William Keel, University of Alabama University, Pomona Julia Kennefick, University of Arkansas Matthew Price, Oregon State University Steve Kipp, University of Minnesota, Mankato Harrison B. Prosper, Florida State University Kurtis Koll, Cameron University Monica Ramirez, Aims College, Colorado Ichishiro Konno, University of Texas at San Christina Reeves-Shull, Richland College Antonio Todd M. Rigg, City College of San Francisco John Kormendy, University of Texas at Austin Elizabeth Roettger, DePaul University Eric Korpela, University of California, Berkeley Roy Rubins, University of Texas at Arlington Arthur Kosowsky, University of Pittsburgh Carl Rutledge, East Central University Kevin Krisciunas, Texas A&M Bob Sackett, Saddleback College David Lamp, Texas Technical University Rex Saffer, Villanova University Ted La Rosa, Kennesaw State University John Safko, University of South Carolina Kristine Larsen, Central Connecticut State University James A. Scarborough, Delta State University Ana Marie Larson, University of Washington Britt Scharringhausen, Ithaca College Stephen Lattanzio, Orange Coast College Ann Schmiedekamp, Pennsylvania State Chris Laws, University of Washington University, Abington Larry Lebofsky, University of Arizona Joslyn Schoemer, Denver Museum of Nature and Patrick Lestrade, Mississippi State University Science Nancy Levenson, University of Kentucky James Schombert, University of Oregon David M. Lind, Florida State University Gregory Seab, University of New Orleans Abraham Loeb, Harvard University Larry Sessions, Metropolitan State College of Denver Michael LoPresto, Henry Ford Community College Anwar Shiekh, Colorado Mesa University William R. Luebke, Modesto Junior College Ralph Siegel, Montgomery College, Germantown Ihor Luhach, Valencia Community College Campus Darrell Jack MacConnell, Community College of Philip I. Siemens, Oregon State University Baltimore City Caroline Simpson, Florida International University Marie Machacek, Massachusetts Institute of Paul Sipiera, William Harper Rainey College Technology Earl F. Skelton, George Washington University Loris Magnani, University of Georgia Evan Skillman, University of Minnesota Steven Majewski, University of Virginia Michael Skrutskie, University of Virginia Phil Matheson, Salt Lake Community College Mark H. Slovak, Louisiana State University John Mattox, Fayetteville State University Norma Small-Warren, Howard University Marles McCurdy, Tarrant County College Jessica Smay, San Jose City College Stacy McGaugh, Case Western University Dale Smith, Bowling Green State University Barry Metz, Delaware County Community College Brent Sorenson, Southern Utah University William Millar, Grand Rapids Community College James R. Sowell, Georgia Technical University Dinah Moche, Queensborough Community College Kelli Spangler, Montgomery County Community of City University, New York College Stephen Murray, University of California, Santa Cruz John Spencer, Southwest Research Institute Zdzislaw E. Musielak, University of Texas at Arlington Darryl Stanford, City College of San Francisco Charles Nelson, Drake University George R. Stanley, San Antonio College Gerald H. Newsom, Ohio State University Peter Stein, Bloomsburg University of Lauren Novatne, Reedley College Pennsylvania Brian Oetiker, Sam Houston State University Adriane Steinacker, University of California, Santa Richard Olenick, University of Dallas Cruz John P. Oliver, University of Florida John Stolar, West Chester University Stacy Palen, Weber State University Irina Struganova, Valencia Community College Russell L. Palma, Sam Houston State University Jack Sulentic, University of Alabama Bryan Penprase, Pomona College C. Sean Sutton, Mount Holyoke College Eric S. Perlman, Florida Institute of Technology Beverley A. P. Taylor, Miami University Peggy Perozzo, Mary Baldwin College Brett Taylor, Radford University Greg Perugini, Burlington County College Donald M. Terndrup, Ohio State University

xx Preface

A01_BENN9068_08_NASTA_FM.indd 20 02/03/17 9:34 AM Frank Timmes, Arizona State University Seth Hornstein, University of Colorado David Trott, Metro State College Dave Jewitt, University of California, Los Angeles David Vakil, El Camino College Julia Kregenow, Penn State University Trina Van Ausdal, Salt Lake Community College Emily Lakdawalla, The Planetary Society Licia Verde, Institute of Cosmological Studies, Hal Levison, Southwest Research Institute Barcelona Mario Livio, Space Telescope Science Institute Nicole Vogt, New Mexico State University J. McKim Malville, University of Colorado Darryl Walke, Rariton Valley Community College Geoff Marcy, University of California, Berkeley, Fred Walter, State University of New York, Stony and San Francisco State University Brook Mark Marley, Ames Research Center James Webb, Florida International University Linda Martel, University of Hawaii Mark Whittle, University of Virginia Kevin McLin, University of Colorado Paul J. Wiita, The College of New Jersey Michael Mendillo, Boston University Lisa M. Will, Mesa Community College Steve Mojzsis, University of Colorado Jonathan Williams, University of Hawaii Francis Nimmo, University of California, Grant Wilson, University of Massachusetts, Amherst Santa Cruz J. Wayne Wooten, Pensacola Junior College Tyler Nordgren, University of Redlands Scott Yager, Brevard College Rachel Osten, Space Telescope Science Institute Andrew Young, Casper College Bob Pappalardo, Jet Propulsion Laboratory Arthur Young, San Diego State University Bennett Seidenstein, Arundel High School Tim Young, University of North Dakota Michael Shara, American Museum of Natural Min S. Yun, University of Massachusetts, Amherst History Dennis Zaritsky, University of Arizona Evan Skillman, University of Minnesota Robert L. Zimmerman, University of Oregon Brad Snowder, Western Washington University Bob Stein, Michigan State University In addition, we thank the following colleagues who Glen Stewart, University of Colorado helped us clarify technical points or checked the accu- John Stolar, West Chester University racy of technical discussions in the book: Jeff Taylor, University of Hawaii Caspar Amman, NCAR Dave Tholen, University of Hawaii Nahum Arav, Virginia Technical University Nick Thomas, University of Bern Phil Armitage, University of Colorado Dimitri Veras, Cambridge University Thomas Ayres, University of Colorado John Weiss, Carleton College Cecilia Barnbaum, Valdosta State University Francis Wilkin, Union College Rick Binzel, Massachusetts Institute of Technology Jeremy Wood, Hazard Community College Howard Bond, Space Telescope Science Institute Jason Wright, Penn State University David Brain, University of Colorado Don Yeomans, Jet Propulsion Laboratory Humberto Campins, University of Central Florida Robin Canup, Southwest Research Institute Finally, we thank the many people who have greatly Clark Chapman, Southwest Research Institute influenced our outlook on education and our perspec- Kelly Cline, Carroll College tive on the universe over the years, including Tom Ayres, Josh Colwell, University of Central Florida Fran Bagenal, Forrest Boley, Robert A. Brown, George James Cooney, University of Central Florida Dulk, Erica Ellingson, Katy Garmany, Jeff Goldstein, Mark Dickinson, National Optical Astronomy David Grinspoon, Robin Heyden, Don Hunten, Geoffrey Observatory Marcy, Joan Marsh, Catherine McCord, Dick McCray, Jim Dove, Metropolitan State College of Denver Dee Mook, Cherilynn Morrow, Charlie Pellerin, Carl Doug Duncan, University of Colorado Sagan, Mike Shull, John Spencer, and John Stocke. Dan Fabrycky, University of Chicago Jeff Bennett Harry Ferguson, Space Telescope Science Institute Megan Donahue Andrew Hamilton, University of Colorado Todd Henry, Georgia State University Nick Schneider Dennis Hibbert, Everett Community College Mark Voit

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A01_BENN9068_08_NASTA_FM.indd 21 02/03/17 9:34 AM A bout the Authors

Jeffrey Bennett Megan Donahue Jeffrey Bennett, a recipient Megan Donahue is a full pro- of the American Institute of fessor in the Department of Physics Science Communica- Physics and Astronomy at tion Award, holds a B.A. in Michigan State University biophysics (UC San Diego), (MSU) and a Fellow of the and an M.S. and Ph.D. in American Association for astrophysics (University of the Advancement of Science. Colorado). He specializes in science and math edu- Her current research is mainly about using X-ray, UV, cation and has taught at every level from preschool infrared, and visible light to study galaxies and clus- through graduate school. Career highlights include ters of galaxies: their contents—dark matter, hot gas, serving 2 years as a visiting senior scientist at NASA galaxies, active galactic nuclei—and what they reveal headquarters, where he developed programs to build about the contents of the universe and how galaxies stronger links between research and education, and form and evolve. She grew up on a farm in Nebraska proposing and helping to develop the Voyage scale and received an S.B. in physics from MIT, where she model solar system on the National Mall (Washington, began her research career as an X-ray astronomer. She DC). He is the lead author of textbooks in astronomy, has a Ph.D. in astrophysics from the University of astrobiology, mathematics, and statistics, and of criti- Colorado. Her Ph.D. thesis on theory and optical obser- cally acclaimed books for the public including Beyond vations of intergalactic and intracluster gas won the UFOs (Princeton University Press, 2008/2011), Math for 1993 Trumpler Award from the Astronomical Society Life (Bid Kid Science, 2014), What Is Relativity? (Colum- for the Pacific for an outstanding astrophysics doc- bia University Press, 2014), and On Teaching Science toral dissertation in North America. She continued (Big Kid Science, 2014). He is also the author of six sci- postdoctoral research as a Carnegie Fellow at Carne- ence picture books for children, including Max Goes gie Observatories in Pasadena, California, and later as to the Moon, The Wizard Who Saved the World, and I, an STScI Institute Fellow at Space Telescope. Megan Humanity; all six have been launched to the Interna- was a staff astronomer at the Space Telescope Science tional Space Station and read aloud by astronauts for Institute until 2003, when she joined the MSU faculty. NASA’s Story Time From Space program. Dr. Bennett Megan is married to Mark Voit, and they collaborate on lives in Boulder, CO with his wife, children, and dog. many projects, including this textbook, over 50 peer- His personal website is www.jeffreybennett.com. reviewed astrophysics papers, and the raising of their children, Michaela, Sebastian, and Angela. Megan has run three full marathons, including Boston. These days she does trail running, orienteers, and plays piano and bass guitar for fun and no profit.

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A01_BENN9068_08_NASTA_FM.indd 22 02/03/17 9:34 AM Nicholas Schneider Mark Voit Nicholas Schneider is an asso- Mark Voit is a professor in ciate professor in the Depart- the Department of Physics ment of Astrophysical and and Astronomy and Associ- Planetary Sciences at the ate Dean for Undergraduate University of Colorado and a Studies at Michigan State Uni- researcher in the Laboratory versity. He earned his A.B. for Atmospheric and Space in astrophysical sciences at Physics. He received his B.A. in physics and astronomy Princeton University and his Ph.D. in astrophysics at from Dartmouth College in 1979 and his Ph.D. in plan- the University of Colorado in 1990. He continued his etary science from the University of Arizona in 1988. studies at the California Institute of Technology, where In 1991, he received the National Science Foundation’s he was a research fellow in theoretical astrophysics, Presidential Young Investigator Award. His research and then moved on to Johns Hopkins University as a interests include planetary atmospheres and plan- Hubble Fellow. Before going to Michigan State, Mark etary astronomy. One research focus is the odd case worked in the Office of Public Outreach at the Space of Jupiter’s moon Io. Another is the mystery of Mars’s Telescope, where he developed museum exhibitions lost atmosphere, which he hopes to answer by leading about the Hubble Space Telescope and helped design the Imaging UV Spectrograph team on NASA’s MAVEN NASA’s award-winning HubbleSite. His research inter- mission now orbiting Mars. Nick enjoys teaching at all ests range from interstellar processes in our own gal- levels and is active in efforts to improve undergraduate axy to the clustering of galaxies in the early universe, astronomy education. In 2010 he received the Boulder and he is a Fellow of the American Association for the Faculty Assembly’s Teaching Excellence Award. Off the Advancement of Science. He is married to coauthor job, Nick enjoys exploring the outdoors with his family Megan Donahue, and cooks terrific meals for her and and figuring out how things work. their three children. Mark likes getting outdoors when- ever possible and particularly enjoys running, moun- tain biking, canoeing, orienteering, and adventure racing. He is also author of the popular book Hubble Space Telescope: New Views of the Universe.

About the Authors xxiii

A01_BENN9068_08_NASTA_FM.indd 23 02/03/17 9:34 AM H ow to Succeed in Your Astronomy Course

If Your Times for Reading the Times for Homework As- Times for Review and Test Prepara- Total Study Course Is Assigned Text (per week) signments (per week) tion (average per week) Time (per week) 3 credits 2 to 4 hours 2 to 3 hours 2 hours 6 to 9 hours 4 credits 3 to 5 hours 2 to 4 hours 3 hours 8 to 12 hours 5 credits 3 to 5 hours 3 to 6 hours 4 hours 10 to 15 hours

T he Key to Success: Study Time on the pages to remind yourself of ideas you’ll The single most important key to success in any college want to review later. Take notes as you read, but course is to spend enough time studying. A general rule avoid using a highlight pen (or a highlighting tool of thumb for college classes is that you should expect to if you are using an e-book), which makes it too study about 2 to 3 hours per week outside of class for each easy to highlight mindlessly. unit of credit. For example, based on this rule of thumb, 4. After reading the chapter once, go back through a student taking 15 credit hours should expect to spend and read the boxed features. 30 to 45 hours each week studying outside of class. Com- 5. Review the Chapter Summary, ideally by trying to bined with time in class, this works out to a total of 45 to answer the Learning Goal questions for yourself 60 hours spent on academic work—not much more than before reading the given answers. the time a typical job requires, and you get to choose your ■ After completing the reading as outlined above, own hours. Of course, if you are working while you attend test your understanding with the end-of-chapter school, you will need to budget your time carefully. exercises. A good way to begin is to make sure As a rough guideline, your study time might be divided you can answer all of the Review and Quick Quiz as shown in the table above. If you find that you are spend- Questions; if you don’t know an answer, look back ing fewer hours than these guidelines suggest, you can through the chapter until you figure it out. probably improve your grade by studying longer. If you ■ Visit the MasteringAstronomy® site and make use are spending more hours than these guidelines suggest, of resources that will help you further build your you may be studying inefficiently; in that case, you should understanding. These resources have been developed talk to your instructor about how to study more effectively. specifically to help you learn the most important U sing This Book ideas in your course, and they have been extensively tested to make sure they are effective. They really do Each chapter in this book is designed to make it easy for work, and the only way you’ll gain their benefits is you to study effectively and efficiently. To get the most by going to the website and using them. out of each chapter, you might wish to use the following study plan. G eneral Strategies for Studying ■ A textbook is not a novel, and you’ll learn best by ■ Budget your time effectively. Studying 1 or 2 hours each reading the elements of this text in the following order: day is more effective, and far less painful, than studying 1. Start by reading the Learning Goals and the all night before homework is due or before exams. introductory paragraphs at the beginning of the ■ Engage your brain. Learning is an active process, chapter so that you’ll know what you are trying not a passive experience. Whether you are reading, to learn. listening to a lecture, or working on assignments, 2. Get an overview of key concepts by studying the always make sure that your mind is actively illustrations and their captions and annotations. engaged. If you find your mind drifting or find The illustrations highlight most major concepts, yourself falling asleep, make a conscious effort to so this “illustrations first” strategy gives you an revive yourself, or take a break if necessary. opportunity to survey the concepts before you ■ Don’t miss class. Listening to lectures and participating read about them in depth. You will find the two- in discussions is much more effective than reading page Cosmic Context figures especially useful. someone else’s notes. Active participation will help 3. Read the chapter narrative, trying the Think you retain what you are learning. Also, be sure to About It questions and the See It for Yourself complete any assigned reading before the class in activities as you go along, but save the boxed which it will be discussed. This is crucial, since class features (e.g., Common Misconceptions, Special lectures and discussions are designed to help reinforce Topics) to read later. As you read, make notes key ideas from the reading.

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A01_BENN9068_08_NASTA_FM.indd 24 02/03/17 9:34 AM ■ Take advantage of resources offered by your professor, requires “extra” effort, it serves two important purposes whether it be email, office hours, review sessions, directly related to learning: online chats, or other opportunities to talk to and get 1. The effort you expend in clearly explaining to know your professor. Most professors will go out of your work solidifies your learning. In particular, their way to help you learn in any way that they can. research has shown that writing and speaking ■ Start your homework early. The more time you trigger different areas of your brain. Writing allow yourself, the easier it is to get help if you something down—even when you think you already need it. If a concept gives you trouble, do additional understand it—reinforces your learning by involving reading or studying beyond what has been assigned. other areas of your brain. And if you still have trouble, ask for help: You surely 2. If you make your work clear and self-contained (that can find friends, peers, or teachers who will be glad is, make it a document that you can read without to help you learn. referring to the questions in the text), you will have ■ Working together with friends can be valuable in a much more useful study guide when you review helping you understand difficult concepts, but be for a quiz or exam. sure that you learn with your friends and do not become dependent on them. The following guidelines will help ensure that your ■ Don’t try to multitask. A large body of research assignments meet the standards of collegiate quality: shows that human beings simply are not good at ■ Always use proper grammar, proper sentence and multitasking: When we attempt it, we do more poorly paragraph structure, and proper spelling. Do not use at all of the individual tasks. And in case you think you texting shorthand. are an exception, the same research found that those ■ Make all answers and other writing fully self-contained. people who believed they were best at multitasking A good test is to imagine that a friend will be reading were actually the worst! So when it is time to study, your work and to ask yourself whether the friend will turn off your electronic devices, find a quiet spot, and understand exactly what you are trying to say. It is also concentrate on focusing your efforts. helpful to read your work out loud to yourself, making Preparing for Exams sure that it sounds clear and coherent. ■ In problems that require calculation: ■ Study the Review Questions, and rework problems and other assignments; try additional questions to 1. Be sure to show your work clearly so that both you be sure you understand the concepts. Study your and your instructor can follow the process you used performance on assignments, quizzes, or exams to obtain an answer. Also, use standard mathematical from earlier in the term. symbols, rather than “calculator-ese.” For example, ■ show multiplication with the 3 symbol (not with an Work through the relevant chapter quizzes 5 and other study resources available at the asterisk), and write 10 , not 10^5 or 10E5. MasteringAstronomy® site. 2. Check that word problems have word answers. ■ Study your notes from lectures and discussions. Pay That is, after you have completed any necessary attention to what your instructor expects you to calculations, make sure that any problem stated know for an exam. in words is answered with one or more complete ■ Reread the relevant sections in the textbook, paying sentences that describe the point of the problem special-attention to notes you have made on the pages. and the meaning of your solution. ■ Study individually before joining a study group with 3. Express your word answers in a way that would friends. Study groups are effective only if every be meaningful to most people. For example, individual comes prepared to contribute. most people would find it more meaningful if ■ Don’t stay up too late before an exam. Don’t eat a you expressed a result of 720 hours as 1 month. big meal within an hour of the exam (thinking is Similarly, if a precise calculation yields an answer more difficult when blood is being diverted to the of 9,745,600 years, it may be more meaningfully digestive system). expressed in words as “nearly 10 million years.” ■ Try to relax before and during the exam. If you have ■ Include illustrations whenever they help explain studied effectively, you are capable of doing well. your answer, and make sure your illustrations Staying relaxed will help you think clearly. are neat and clear. For example, if you graph by hand, use a ruler to make straight lines. If you Presenting Homework and Writing use software to make illustrations, be careful not Assignments to make them overly cluttered with unnecessary All work that you turn in should be of collegiate qual- features. ity: neat and easy to read, well organized, and demon- ■ If you study with friends, be sure that you turn in strating mastery of the subject matter. Future employers your own work stated in your own words—you and teachers will expect this quality of work. Moreover, should avoid anything that might give even the although submitting homework of collegiate quality appearance of possible academic dishonesty.

How to Succeed in Your Astronomy Course xxv

A01_BENN9068_08_NASTA_FM.indd 25 02/03/17 9:34 AM F oreword The Meaning of the Cosmic Perspective

by Neil deGrasse Tyson

Astrophysicist Neil deGrasse Long before anyone knew that the universe had a begin- Tyson is the Frederick P. Rose ning, before we knew that the nearest large galaxy lies Director of New York City’s two and a half million light-years from Earth, before we Hayden Planetarium at the knew how stars work or whether atoms exist, James American Museum of Natu- Ferguson’s enthusiastic introduction to his favorite sci- ral History. He has written ence rang true. numerous books and articles, But who gets to think that way? Who gets to celebrate has hosted the PBS series this cosmic view of life? Not the migrant farm worker. NOVA scienceNOW and the Not the sweatshop worker. Certainly not the homeless globally popular Cosmos: person rummaging through the trash for food. You need A Spacetime Odyssey, and © Neil deGrasse Tyson the luxury of time not spent on mere survival. You need was named one of the “Time to live in a nation whose government values the search 100”—Time Magazine’s list of the 100 most influential to understand humanity’s place in the universe. You people in the world. He contributed this essay about the need a society in which intellectual pursuit can take you meaning of “The Cosmic Perspective,” abridged from his to the frontiers of discovery, and in which news of your 100th essay written for Natural History magazine. discoveries can be routinely disseminated. When I pause and reflect on our expanding universe, Of all the sciences cultivated by mankind, with its galaxies hurtling away from one another, embed- ded with the ever-stretching, four-dimensional fabric of Astronomy is acknowledged to be, and space and time, sometimes I forget that uncounted peo- undoubtedly is, the most sublime, the most ple walk this Earth without food or shelter, and that chil- interesting, and the most useful. For, by knowledge dren are disproportionately represented among them. derived from this science, not only the bulk of the When I pore over the data that establish the mysteri- ous presence of dark matter and dark energy throughout Earth is discovered …; but our very faculties are the universe, sometimes I forget that every day—every enlarged with the grandeur of the ideas it conveys, twenty-four-hour rotation of Earth—people are killing our minds exalted above [their] low contracted and being killed. In the name of someone’s ideology. prejudices. When I track the orbits of asteroids, comets, and planets, each one a pirouetting dancer in a cosmic bal- —James Ferguson, Astronomy Explained Upon Sir let choreographed by the forces of gravity, sometimes Isaac Newton’s Principles, and Made Easy To Those I forget that too many people act in wanton disregard Who Have Not Studied Mathematics (1757) for the delicate interplay of Earth’s atmosphere, oceans, and land, with consequences that our children and our children’s children will witness and pay for with their health and well-being. And sometimes I forget that powerful people rarely do all they can to help those who cannot help themselves. I occasionally forget those things because, however big the world is—in our hearts, our minds, and our out- size atlases—the universe is even bigger. A depressing thought to some, but a liberating thought to me. Consider an adult who tends to the traumas of a child: a broken toy, a scraped knee, a schoolyard bully. Adults know that kids have no clue what constitutes a genuine problem, because inexperience greatly limits their childhood perspective. As grown-ups, dare we admit to ourselves that we, too, have a collective immaturity of view? Dare we admit that our thoughts and behaviors spring from a

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A01_BENN9068_08_NASTA_FM.indd 26 02/03/17 9:34 AM belief that the world revolves around us? Part the cur- the water you just drank passed through the kidneys of tains of society’s racial, ethnic, religious, national, and Socrates, Genghis Khan, and Joan of Arc. cultural conflicts, and you find the human ego turning How about air? Also vital. A single breathful draws the knobs and pulling the levers. in more air molecules than there are breathfuls of air in Now imagine a world in which everyone, but espe- Earth’s entire atmosphere. That means some of the air cially people with power and influence, holds an you just breathed passed through the lungs of Napoleon, expanded view of our place in the cosmos. With that Beethoven, Lincoln, and Billy the Kid. perspective, our problems would shrink—or never arise Time to get cosmic. There are more stars in the uni- at all—and we could celebrate our earthly differences verse than grains of sand on any beach, more stars than while shunning the behavior of our predecessors who seconds have passed since Earth formed, more stars slaughtered each other because of them. than words and sounds ever uttered by all the humans

■ ■ ■ who ever lived. Want a sweeping view of the past? Our unfolding Back in February 2000, the newly rebuilt Hayden cosmic perspective takes you there. Light takes time to Planetarium featured a space show called “Passport to reach Earth’s observatories from the depths of space, the Universe,” which took visitors on a virtual zoom and so you see objects and phenomena not as they are from New York City to the edge of the cosmos. En route but as they once were. That means the universe acts like the audience saw Earth, then the solar system, then the a giant time machine: the farther away you look, the fur- 100 billion stars of the Milky Way galaxy shrink to barely ther back in time you see—back almost to the beginning visible dots on the planetarium dome. of time itself. Within that horizon of reckoning, cosmic I soon received a letter from an Ivy League professor evolution unfolds continuously, in full view. of psychology who wanted to administer a questionnaire Want to know what we’re made of? Again, the cos- to visitors, assessing the depth of their depression after mic perspective offers a bigger answer than you might viewing the show. Our show, he wrote, elicited the most expect. The chemical elements of the universe are dramatic feelings of smallness he had ever experienced. forged in the fires of high-mass stars that end their lives How could that be? Every time I see the show, I feel in stupendous explosions, enriching their host galaxies alive and spirited and connected. I also feel large, know- with the chemical arsenal of life as we know it. We are ing that the goings-on within the three-pound human not simply in the universe. The universe is in us. Yes, brain are what enabled us to figure out our place in the we are stardust. universe. Allow me to suggest that it’s the professor, not I, who ■ ■ ■ has misread nature. His ego was too big to begin with, Again and again across the centuries, cosmic dis- inflated by delusions of significance and fed by cultural coveries have demoted our self-image. Earth was once assumptions that human beings are more important assumed to be astronomically unique, until astronomers than everything else in the universe. learned that Earth is just another planet orbiting the Sun. In all fairness to the fellow, powerful forces in society Then we presumed the Sun was unique, until we learned leave most of us susceptible. As was I … until the day that the countless stars of the night sky are suns them- I learned in biology class that more bacteria live and selves. Then we presumed our galaxy, the Milky Way, work in one centimeter of my colon than the number of was the entire known universe, until we established that people who have ever existed in the world. That kind the countless fuzzy things in the sky are other galaxies, of information makes you think twice about who—or dotting the landscape of our known universe. what—is actually in charge. The cosmic perspective flows from fundamental From that day on, I began to think of people not as knowledge. But it’s more than just what you know. It’s the masters of space and time but as participants in a also about having the wisdom and insight to apply that great cosmic chain of being, with a direct genetic link knowledge to assessing our place in the universe. And across species both living and extinct, extending back its attributes are clear: nearly 4 billion years to the earliest single-celled organ- ■ The cosmic perspective comes from the frontiers isms on Earth. of science, yet is not solely the provenance of the ■ ■ ■ scientist. It belongs to everyone. Need more ego softeners? Simple comparisons of ■ The cosmic perspective is humble. quantity, size, and scale do the job well. ■ The cosmic perspective is spiritual—even Take water. It’s simple, common, and vital. There redemptive—but is not religious. are more molecules of water in an eight-ounce cup of ■ The cosmic perspective enables us to grasp, in the the stuff than there are cups of water in all the world’s same thought, the large and the small. oceans. Every cup that passes through a single person ■ The cosmic perspective opens our minds to and eventually rejoins the world’s water supply holds extraordinary ideas but does not leave them so open enough molecules to mix 1,500 of them into every other that our brains spill out, making us susceptible to cup of water in the world. No way around it: some of believing anything we’re told.

foreword xxvii

A01_BENN9068_08_NASTA_FM.indd 27 02/03/17 9:34 AM ■ The cosmic perspective opens our eyes to the reveal them. We might further ponder how those discov- universe, not as a benevolent cradle designed to eries may one day transform life on Earth. nurture life but as a cold, lonely, hazardous place. Absent such curiosity, we are no different from the ■ The cosmic perspective shows Earth to be a mote, provincial farmer who expresses no need to venture but a precious mote and, for the moment, the only beyond the county line, because his forty acres meet home we have. all his needs. Yet if all our predecessors had felt that ■ The cosmic perspective finds beauty in the images way, the farmer would instead be a cave dweller, chas- of planets, moons, stars, and nebulae but also ing down his dinner with a stick and a rock. celebrates the laws of physics that shape them. During our brief stay on planet Earth, we owe our- ■ The cosmic perspective enables us to see beyond selves and our descendants the opportunity to explore— our circumstances, allowing us to transcend the in part because it’s fun to do. But there’s a far nobler primal search for food, shelter, and sex. reason. The day our knowledge of the cosmos ceases ■ The cosmic perspective reminds us that in space, to expand, we risk regressing to the childish view that where there is no air, a flag will not wave—an the universe figuratively and literally revolves around indication that perhaps flag waving and space us. In that bleak world, arms-bearing, resource-hungry exploration do not mix. people and nations would be prone to act on their “low ■ The cosmic perspective not only embraces our contracted prejudices.” And that would be the last gasp genetic kinship with all life on Earth but also values of human enlightenment—until the rise of a visionary our chemical kinship with any yet-to-be discovered new culture that could once again embrace the cosmic life in the universe, as well as our atomic kinship perspective. with the universe itself.

■ ■ ■ At least once a week, if not once a day, we might Copyright © Neil deGrasse Tyson 2007. Adapted from each ponder what cosmic truths lie undiscovered before the essay “Cosmic Perspectives,” which first appeared us, perhaps awaiting the arrival of a clever thinker, an in Natural History magazine, April 2007. Used with ingenious experiment, or an innovative space mission to permission.

xxviii foreword

A01_BENN9068_08_NASTA_FM.indd 28 02/03/17 9:34 AM