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Astronomy Today (8th Edition)

With Astronomy Today, Eighth Edition, trusted authors Eric Chaisson and Steve McMillan communicate their excitement about astronomy, delivering current and thorough science with insightful pedagogy. The text emphasizes critical thinking and visualization, and it focuses on the process of scientific discovery, teaching students “how we know what we know.” The Eighth Edition has been thoroughly updated with the latest astronomical discoveries and theories and improved pedagogical featur

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Astronomy Today (8th Edition)

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  1. Astronomy Today 8e

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  3. Astronomy Today 8e Eric Chaisson Harvard University Steve McMillan Drexel University Boston Columbus Indianapolis New York San Francisco Upper Saddle River Amsterdam Cape Town Dubai London Madrid Milan Munich Paris Montréal Toronto Delhi Mexico City São Paulo Sydney Hong Kong Seoul Singapore Taipei Tokyo

  4. Publisher: Jim Smith Executive Editor: Nancy Whilton Editorial Manager: Laura Kenney Project Editor: Tema Goodwin Content Producers: Kate Brayton, Ziki Dekel Development Editor: Barbara Price Director of Marketing: Christy Lesko Marketing Manager: Will Moore Director of Product Management Services: Erin Gregg Team Lead, Program and Project Management: Corinne Benson Compositor: Cenveo® Publisher Services Production Service: Thistle Hill Publishing Services Illustrations: Rolin Graphics Inc. Design Manager: Mark Ong Interior and Cover Design: Jeanne Calabrese Manufacturing Buyer: Jeffrey Sargent Specialist, Rights and Permissions: Joseph Croscup Image Permissions Coordinator: Maya Melunchuk Photo Research: Stefanie Ramsay Cover Printer: Lehigh-Phoenix Printer and Binder: R. R. Donnelley Cover Images: Main Edition: ESO/S. Guisard (www.eso.org/~sguisard) Vol. 1: The Solar System: NASA, JPL-Caltech, MSSS, Mastcam Vol. 2: Stars and Galaxies: ESO/F. Comeron Copyright © 2014, 2011, 2008, 2005 Pearson Education, Inc., 1301 Sansome St., San Francisco, CA 94111. All rights reserved. Manufactured in the United States of America. This publication is protected by Copyright and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. To obtain permission(s) to use material from this work, please submit a written request to Pearson Education, Inc., Permissions Department, 1900 E. Lake Ave., Glenview, IL 60025. For information regarding permissions, call (847) 486-2635. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed in initial caps or all caps. MasteringAstronomy® is a trademark, in the U.S. and/or other countries, of Pearson Education, Inc. or its affiliates. Library of Congress Cataloging-in-Publication Data Chaisson, Eric, author. Astronomy today / Eric Chaisson, Harvard University, Steve McMillan, Drexel University. — Eighth edition. pages cm Includes bibliographical references and index. ISBN 978-0-321-90167-5 (student edition) — ISBN 978-0-321-90971-8 (volume 1) — ISBN 978-0-321-90972-5 (volume 2) — ISBN 978-0-13-341279-6 (nasta) 1. Astronomy—Textbooks. I. McMillan, S. (Stephen), 1955– author. II. Title. QB43.3.C48 2014 520—dc23 2013019295 ISBN 10 digit 0-321-90167-3; 13-digit 978-0-321-90167-5 (Student edition) ISBN 10-digit 0-321-90971-2; 13-digit 978-0-321-90971-8 (Volume 1) ISBN 10-digit 0-321-90972-0; 13-digit 978-0-321-90972-5 (Volume 2) ISBN 10-digit 0-13-341279-2; 13-digit 978-0-13-341279-6 (NASTA) www.pearsonhighered.com 1 2 3 4 5 6 7 8 9 10—VHC—19 18 17 16 15 14 13

  5. Brief Contents Part One: Astronomy and the Universe 2 1 2 3 4 5 Charting the Heavens: The Foundations of Astronomy 4 The Copernican Revolution: The Birth of Modern Science 32 Radiation: Information from the Cosmos 58 Spectroscopy: The Inner Workings of Atoms 78 Telescopes: The Tools of Astronomy 98 Part Two: Our Planetary System 132 10 11 12 13 14 15 6 7 8 9 The Solar System: Comparative Planetology and Formation Models 134 Earth: Our Home in Space 160 The Moon and Mercury: Scorched and Battered Worlds 188 Venus: Earth’s Sister Planet 216 Mars: A Near Miss for Life? 236 Jupiter: Giant of the Solar System 264 Saturn: Spectacular Rings and Mysterious Moons 290 Uranus and Neptune: The Outer Worlds of the Solar System 318 Solar System Debris: Keys to Our Origin 338 Exoplanets: Planetary Systems Beyond Our Own 366 Part Three: Stars and Stellar Evolution 386 16 17 18 19 20 21 22 The Sun: Our Parent Star 388 The Stars: Giants, Dwarfs, and the Main Sequence 420 The Interstellar Medium: Gas and Dust among the Stars 448 Star Formation: A Traumatic Birth 468 Stellar Evolution: The Life and Death of a Star 494 Stellar Explosions: Novae, Supernovae, and the Formation of the Elements 520 Neutron Stars and Black Holes: Strange States of Matter 542 Part Four: Galaxies and Cosmology 574 23 24 25 26 27 28 The Milky Way Galaxy: A Spiral in Space 576 Galaxies: Building Blocks of the Universe 606 Galaxies and Dark Matter: The Large-Scale Structure of the Cosmos 638 Cosmology: The Big Bang and the Fate of the Universe 666 The Early Universe: Toward the Beginning of Time 688 Life in the Universe: Are We Alone? 714

  6. Contents About the Authors  xxi Preface  xxiii Part One: Astronomy and the Universe2 1 Charting the Heavens The Foundations of Astronomy  4 1.1 Our Place in Space  6 1.2 Scientific Theory and the Scientific Method  8 1.3 The “Obvious” View  10 1.4 Earth’s Orbital Motion  13 More Precisely 1-1 Angular Measure  14 1.5 The Motion of the Moon  18 1.6 The Measurement of Distance  24 More Precisely 1-2 Measuring Distances with Geometry  28 Chapter Review  29 2 The Copernican Revolution The Birth of Modern Science  32 2.1 Ancient Astronomy  34 2.2 The Geocentric Universe  36 2.3 The Heliocentric Model of the Solar System  39 Discovery 2-1 Foundations of the Copernican Revolution  40 2.4 The Birth of Modern Astronomy  41 2.5 The Laws of Planetary Motion  44 More Precisely 2-1 Some Properties of Planetary Orbits  46 2.6 The Dimensions of the Solar System  47 2.7 Newton’s Laws  49 2.8 Newtonian Mechanics  52 More Precisely 2-2 Weighing the Sun  54 Chapter Review  56 3 Radiation Information from the Cosmos  58 3.1 Information from the Skies  60 3.2 Waves in What?  63 3.3 Electromagnetic Spectrum  65 Discovery 3-1 The Wave Nature of Radiation  67 3.4 Thermal Radiation  68 More Precisely 3-1 The Kelvin Temperature Scale  69 More Precisely 3-2 More About the Radiation Laws  72 3.5 The Doppler Effect  73 More Precisely 3-3 Measuring Velocities with the Doppler Effect  75 Chapter Review  76

  7. Contentsvii 4 Spectroscopy The Inner Workings of Atoms  78 4.1 Spectral Lines  80 4.2 Atoms and Radiation  84 More Precisely 4-1 The Hydrogen Atom  86 4.3 The Formation of Spectral Lines  87 Discovery 4-1 The Photoelectric Effect  88 4.4 Molecules  91 4.5 Spectral-Line Analysis  92 Chapter Review  95 5 Telescopes The Tools of Astronomy  98 5.1 Optical Telescopes  100 5.2 Telescope Size  105 5.3 Images and Detectors  109 5.4 High-Resolution Astronomy  111 5.5 Radio Astronomy  114 5.6 Interferometry  118 5.7 Space-Based Astronomy  121 Discovery 5-1 The ALMA Array  124 5.8 Full-Spectrum Coverage  128 Chapter Review  129 Part Two: Our Planetary System132 6 The Solar System Comparative Planetology and Formation Models  134 6.1 An Inventory of the Solar System  136 6.2 Measuring the Planets  138 6.3 The Overall Layout of the Solar System  139 6.4 Terrestrial and Jovian Planets  140 Discovery 6-1 Gravitational “Slingshots”  142 6.5 Interplanetary Matter  143 6.6 How Did the Solar System Form?  144 Discovery 6-2 Spacecraft Exploration of the Solar System  146 More Precisely 6-1 Angular Momentum  149 6.7 Jovian Planets and Planetary Debris  152 Chapter Review  156 7 Earth Our Home in Space  160 7.1 Overall Structure of Planet Earth  162 7.2 Earth’s Atmosphere  162 More Precisely 7-1 Why Is the Sky Blue?  165

  8. viii Contents Discovery 7-1 The Greenhouse Effect and Global Warming  167 7.3 Earth’s Interior  168 More Precisely 7-2 Radioactive Dating  172 7.4 Surface Activity  173 7.5 Earth’s Magnetosphere  180 7.6 The Tides  182 Chapter Review  185 8 The Moon and Mercury Scorched and Battered Worlds  188 8.1 Orbital Properties  190 8.2 Physical Properties  191 8.3 Surface Features on the Moon and Mercury  192 8.4 Rotation Rates  195 More Precisely 8-1 Why Air Sticks Around  196 Discovery 8-1 Lunar Exploration  198 8.5 Lunar Cratering and Surface Composition  201 8.6 The Surface of Mercury  206 8.7 Interiors  208 8.8 The Origin of the Moon  210 8.9 Evolutionary History of the Moon and Mercury  211 Chapter Review  213 9 Venus Earth’s Sister Planet  216 9.1 Orbital Properties  218 9.2 Physical Properties  219 Long-Distance Observations of Venus  220 9.3 9.4 The Surface of Venus  221 The Atmosphere of Venus  228 9.5 Venus’s Magnetic Field and Internal Structure  232 Chapter Review  233 9.6 10 Mars A Near Miss for Life?  236 10.1 Orbital Properties  238 10.2 Physical Properties  239 10.3 Long-Distance Observations of Mars  239 10.4 The Martian Surface  240 10.5 Water on Mars  244 Discovery 10-1 Life on Mars?  250 10.6 The Martian Atmosphere  256 10.7 Martian Internal Structure   259 10.8 The Moons of Mars  260 Chapter Review  261

  9. Contentsix 11 Jupiter Giant of the Solar System  264 11.1 Orbital and Physical Properties  266 11.2 Jupiter Atmosphere  268 Discovery 11-1 A Cometary Impact  274 11.3 Internal Structure  274 Discovery 11-2 Almost a Star?  276 11.4 Jupiter’s Magnetosphere  277 11.5 The Moons of Jupiter  279 11.6 Jupiter’s Ring  287 Chapter Review  287 12 Saturn Spectacular Rings and Mysterious Moons  290 12.1 Orbital and Physical Properties  292 12.2 Saturn’s Atmosphere  293 12.3 Saturn’s Interior and Magnetosphere  296 12.4 Saturn’s Spectacular Ring System  298 12.5 The Moons of Saturn  304 Discovery 12-1 Dancing Among Saturn’s Moons  306 Chapter Review  315 13 Uranus and Neptune The Outer Worlds of the Solar System  318 13.1 The Discoveries of Uranus and Neptune  320 13.2 Orbital and Physical Properties  322 13.3 The Atmospheres of Uranus and Neptune  324 13.4 Magnetospheres and Internal Structure  326 13.5 The Moon Systems of Uranus and Neptune  328 13.6 The Rings of the Outermost Jovian Planets  332 Chapter Review  335 14 Solar System Debris Keys to Our Origin  338 14.1 Asteroids  340 14.2 Comets  345 Discovery 14-1 What Killed the Dinosaurs?  350 14.3 Beyond Neptune  353 14.4 Meteroids  358 Chapter Review  363 15 EXOPLANETS Planetary Systems Beyond Our Own  366 15.1 Modeling Planet Formation  368 15.2 Solar System Regularities and Irregularities  369

  10. x Contents 15.3 Searching for Extrasolar Planets  370 15.4 Exoplanet Properties  373 Discovery 15-1 The Closest Exoplanet  376 15.5 Is Our Solar System Unusual?  379 Chapter Review  383 Part Three: Stars and Stellar Evolution  386 16 The Sun Our Parent Star  388 16.1 Physical Properties of the Sun  390 16.2 The Solar Interior  392 Discovery 16-1 Eavesdropping on the Sun  395 16.3 The Sun’s Atmosphere  397 16.4 Solar Magnetism  400 16.5 The Active Sun  405 Discovery 16-2 Solar–Terrestrial Relations  409 16.6 The Heart of the Sun  410 More Precisely 16-1 Fundamental Forces  413 16.7 Observations of Solar Neutrinos  414 More Precisely 16-2 Energy Generation in the Proton–Proton Chain  416 Chapter Review  417 17 The Stars Giants, Dwarfs, and the Main Sequence  420 17.1 The Solar Neighborhood  422 17.2 Luminosity and Apparent Brightness  425 17.3 Stellar Temperatures  428 More Precisely 17-1 More on the Magnitude Scale  430 17.4 Stellar Sizes  432 More Precisely 17-2 Estimating Stellar Radii  433 17.5 The Hertzsprung–Russell Diagram  434 17.6 Extending the Cosmic Distance Scale  437 17.7 Stellar Masses  440 More Precisely 17-3 Measuring Stellar Masses in Binary Stars  443 17.8 Mass and Other Stellar Properties  442 Chapter Review  445 18 The Interstellar Medium Gas and Dust Among The Stars  448 18.1 Interstellar Matter  450 18.2 Emission Nebulae  453 18.3 Dark Dust Clouds  459 18.4 21-Centimeter Radiation  462 18.5 Interstellar Molecules  463 Chapter Review  465

  11. Contentsxi 19 Star Formation A Traumatic Birth  468 19.1 Star-Forming Regions  470 More Precisely 19-1 Competition in Star Formation  471 19.2 The Formation of Stars Like the Sun  472 19.3 Stars of Other Masses  477 19.4 Observations of Cloud Fragments and Protostars  478 Discovery 19-1 Observations of Brown Dwarfs  479 19.5 Shock Waves and Star Formation  484 19.6 Star Clusters  486 Discovery 19-2 Eta Carinae  490 Chapter Review  491 20 Stellar Evolution The Life and Death of a Star  494 20.1 Leaving the Main Sequence  496 20.2 Evolution of a Sun-Like Star  496 20.3 The Death of a Low-Mass Star  502 Discovery 20-1 Learning Astronomy from History  508 20.4 Evolution of Stars More Massive than the Sun  509 Discovery 20-2 Mass Loss from Giant Stars  511 20.5 Observing Stellar Evolution in Star Clusters  512 20.6 Stellar Evolution in Binary Systems  515 Chapter Review  517 21 Stellar Explosions Novae, Supernovae, and the Formation of the Elements  520 21.1 Life after Death for White Dwarfs  522 21.2 The End of a High-Mass Star  524 21.3 Supernovae  526 21.4 The Formation of the Elements  530 Discovery 21-1 Supernova 1987A  532 21.5 The Cycle of Stellar Evolution  538 Chapter Review  539 22 Neutron Stars and Black Holes Strange States of Matter  542 22.1 Neutron Stars  544 22.2 Pulsars  545 22.3 Neutron-Star Binaries  548 22.4 Gamma-Ray Bursts  552 22.5 Black Holes  555 22.6 Einstein’s Theories of Relativity  557 Discovery 22-1 Special Relativity  559 22.7 Space Travel Near Black Holes  561

  12. xii Contents 22.8 Observational Evidence for Black Holes  564 More Precisely 22-1 Tests of General Relativity  566 Discovery 22-2 Gravity Waves: A New Window on the Universe  568 Chapter Review  571 Part Four: Galaxies and Cosmology  574 23 The Milky Way Galaxy A Spiral in Space  576 23.1 Our Parent Galaxy  578 23.2 Measuring the Milky Way  579 Discovery 23-1 Early “Computers”  584 23.3 Galactic Structure  586 23.4 The Formation of the Milky Way  589 23.5 Galactic Spiral Arms  591 Discovery 23-2 Density Waves  594 23.6 The Mass of the Milky Way Galaxy  595 23.7 The Galactic Center  599 Chapter Review  603 24 Galaxies Building Blocks of the Universe  606 24.1 Hubble’s Galaxy Classification  608 24.2 The Distribution of Galaxies in Space  615 24.3 Hubble’s Law  619 More Precisely 24-1 Relativistic Redshifts and Look-Back Time  622 24.4 Active Galactic Nuclei  622 24.5 The Central Engine of an Active Galaxy  630 Chapter Review  635 25 Galaxies and Dark Matter The Large-Scale Structure of the Cosmos  638 25.1 Dark Matter in the Universe  640 25.2 Galaxy Collisions  643 25.3 Galaxy Formation and Evolution  645 Discovery 25-1 The Sloan Digital Sky Survey  651 25.4 Black Holes in Galaxies  652 25.5 The Universe on Large Scales  656 Chapter Review  663 26 Cosmology The Big Bang and the Fate of the Universe  666 26.1 The Universe on the Largest Scales  668 26.2 The Expanding Universe  670 26.3 The Fate of the Cosmos  673

  13. Contentsxiii 26.4 The Geometry of Space  675 More Precisely 26-1 Curved Space  677 26.5 Will the Universe Expand Forever?  678 26.6 Dark Energy and Cosmology  680 Discovery 26-1 Einstein and the Cosmological Constant  681 26.7 The Cosmic Microwave Background  683 Chapter Review  685 27 The Early Universe Toward the Beginning of Time  688 27.1 Back to the Big Bang  690 27.2 Evolution of the Universe  693 More Precisely 27-1 More on Fundamental Forces  694 27.3 Formation of Nuclei and Atoms  697 27.4 The Inflationary Universe  700 27.5 Formation of Structure in the Universe  705 27.6 Cosmic Structure and the Microwave Background  707 Chapter Review  711 28 Life in the Universe Are We Alone?  714 28.1 Cosmic Evolution  716 Discovery 28-1 The Virus  717 28.2 Life in the Solar System  722 28.3 Intelligent Life in the Galaxy  724 28.4 The Search for Extraterrestrial Intelligence  729 Chapter Review  733 Appendices Appendix 1 Scientific Notation  A-1 Appendix 2 Astronomical Measurement  A-2 Appendix 3 Tables  A-3 Glossary G-1 Answers to Check Questions AK-1 Answers to Self-Test Questions AK-6 Photo Credits/Text Permissions C-1 Index I-1 Star Charts S-1

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  15. Online Contents PART ONE: ASTRONOMy AND THE UNIVERSE • ANIMATION/VIDEO EarthCapturesa Temporary Moon 52 • INTERACTIVE FIGURE Orbits 53 • INTERACTIVE FIGURE Escape Speed 55 • ANIMATION/VIDEO MultispectralViews of the Orion Nebula 91 • INTERACTIVE FIGURE Doppler Shift 93 Chapter 5 Telescopes 98 • SELF-GUIDEDTUTORIALTheOpticsofa Simple Lens 101 • SELF-GUIDEDTUTORIALChromatic Aberration 102 • SELF-GUIDEDTUTORIALReflecting Telescopes 103 • ANIMATION/VIDEOHubble Space Telescope in Orbit 104 • ANIMATION/VIDEOGeminiControl Room 107 • INTERACTIVE FIGURE Resolving Power 108 • INTERACTIVEFIGUREConstructing an Image from Colored Filters 110 • ANIMATION/VIDEO Adaptive Optics 114 • ANIMATION/VIDEODeployment of the James Webb Space Telescope 122 • ANIMATION/VIDEO Chandra Light and Data Paths 126 • NARRATED FIGURE Multiple Wavelengths 128 2 Chapter 1 Charting the Heavens 4 • INTERACTIVE FIGURE Constellation Orion 10 • INTERACTIVE FIGURE Celestial Sphere 12 • INTERACTIVE FIGURE Northern Sky 12 • ANIMATION/VIDEO Summer Solstice 13 • INTERACTIVE FIGURE The Zodiac 15 • ANIMATION/VIDEO Winter Solstice 16 • ANIMATION/VIDEO The Earth’s Seasons 16 • INTERACTIVE FIGURE Seasons 16 • ANIMATION/VIDEO The Equinoxes 17 • INTERACTIVE FIGURE Precession 18 • SELF-GUIDEDTUTORIAL Phasesofthe Moon 19 • NARRATED FIGURE Lunar Phases 19 • INTERACTIVE FIGURE Sidereal Month 20 • INTERACTIVE FIGURE Lunar Eclipse 20 • INTERACTIVE FIGURE Types of Solar Eclipse 21 • ANIMATION/VIDEO SolarEclipsein Indiana 21 Chapter 3 Radiation 58 • INTERACTIVE FIGURE Water Wave 61 • INTERACTIVE FIGURE Wave Proper-ties 61 • ANIMATION/VIDEO SolarEclipse Viewed in X-rays 66 • ANIMATION/VIDEO MultispectralView of Orion Nebula 66 • ANIMATION/VIDEO EarthAurorain X-rays 66 • NARRATED INTERACTIVE FIGURE Electromagnetic Spectrum 66 • ANIMATION/VIDEO Fresnel Diffraction 67 • SELF-GUIDEDTUTORIAL Continuous Spectra and Blackbody Radiation 70 • INTERACTIVE FIGURE Astronomical Thermometer 71 • SELF-GUIDEDTUTORIAL Doppler Effect 73 • INTERACTIVE FIGURE Doppler Effect 74 Chapter 4 Spectroscopy 78 PART TWO: OUR PLANETARy SySTEM Chapter 2 The Copernican Revolution 32 • INTERACTIVE FIGURE Continuous and Emission Spectra 81 • SELF-GUIDEDTUTORIAL Emission Spectra 82 • SELF-GUIDEDTUTORIAL Absorption Spectra 82 • INTERACTIVE FIGURE Absorption Spectrum 82 • INTERACTIVE FIGURE Sodium Spectrum 83 • ANIMATION/VIDEO ClassicalHydrogen Atom I 86 • ANIMATION/VIDEO ClassicalHydrogen Atom II 86 • INTERACTIVE FIGURE Atomic Excitation 89 132 Chapter 6 The Solar System 134 • ANIMATION/VIDEORetrogradeMotionof Mars 37 • INTERACTIVE FIGURE Geocentric Model 38 • ANIMATION/VIDEO Geocentric Solar System 39 • ANIMATION/VIDEO HeliocentricSolar System 39 • INTERACTIVE FIGURE Retrograde Motion 41 • INTERACTIVE FIGURE Venus Phases 43 • INTERACTIVE FIGURE Ellipse 45 • INTERACTIVE FIGURE Kepler’s Second Law 46 • ANIMATION/VIDEO AnAstronomical Ruler 139 • ANIMATION/VIDEO TheGas Giants 141 • ANIMATION/VIDEO Sizeand Scale of the Terrestrial Planets I & II 141 • INTERACTIVEFIGURE Gravitational Assist 142 • INTERACTIVEFIGURE Nebular Contraction 145 • ANIMATION/VIDEO SolarSystem Formation 152 xv

  16. • ANIMATION/VIDEO ProtoplanetaryDisk Destruction 153 • ANIMATION/VIDEO Protoplanetary Disks in the Orion Nebula 153 • INTERACTIVEFIGURE Jovian Condensation 153 • ANIMATION/VIDEO TheRotationof Venus 219 • ANIMATION/VIDEO TransitofVenus 220 • ANIMATION/VIDEO Topographyof Venus 222 • ANIMATION/VIDEO FlightOverAlpha Regio 225 • ANIMATION/VIDEO FlightOverSifMons Volcano 225 • ANIMATION/VIDEO GalileanMoons Transit Jupiter 279 • INTERACTIVEFIGURE Galilean Moons 279 • ANIMATION/VIDEO IoCutaway 280 • INTERACTIVEFIGURE Volcanoeson Io 282 • ANIMATION/VIDEO Galileo’s View of Europa 284 • ANIMATION/VIDEO Galileo’s View of Ganymede 285 • ANIMATION/VIDEO JupiterIcyMoons Orbiter Mission 286 Chapter 7 Earth 160 • ANIMATION/VIDEO EarthasSeenby Galileo 164 • ANIMATION/VIDEO NEAR Earth Swingby 164 • ANIMATION/VIDEO OzoneHoleOver the Antarctic 166 • SELF-GUIDEDTUTORIAL The Greenhouse Effect 166 • INTERACTIVEFIGURE Greenhouse Effect 166 • INTERACTIVEFIGURE PlateDrift 178 • ANIMATION/VIDEO Northernand Southern Lights 182 • INTERACTIVEFIGURE SolarandLunar Tides 184 Chapter 10 Mars 236 • ANIMATION/VIDEO Hubble View of Mars 240 • INTERACTIVEFIGURE MarsMap 241 • ANIMATION/VIDEO FlightOver Tharsis 242 • ANIMATION/VIDEO FlightOverMariner Valley 243 • SELF-GUIDEDTUTORIAL Comparative Planetology: Mars 245 • ANIMATION/VIDEO MeteoritesEjected from Mars 251 • ANIMATION/VIDEO Hubble View of Mars Polar Cap 252 • ANIMATION/VIDEO FlightOver Opportunity at Gustav Crater 254 • ANIMATION/VIDEO Mars Rover Landing 254 • ANIMATION/VIDEO FlightOver Columbia Hills 254 • SELF-GUIDEDTUTORIAL Atmospheric Lifetimes 257 • ANIMATION/VIDEO MartianMoons: Phobos & Deimos 260 Chapter 12 Saturn 290 • ANIMATION/VIDEO SaturnCloud Rotation 295 • ANIMATION/VIDEO SaturnRingPlane Crossing 298 • NARRATED FIGURE Roche Limit 299 • INTERACTIVEFIGURE Saturn’sRings, Up Close 301 • ANIMATION/VIDEO Voyager Ring Spokes 302 • ANIMATION/VIDEO SaturnSatellite Transit 303 • ANIMATION/VIDEO Huygens Landing on Titan 309 Chapter 8 The Moon and Mercury 188 • ANIMATION/VIDEO Transitof Mercury 191 • ANIMATION/VIDEO FullRotationof Moon 193 • ANIMATION/VIDEO LunarFlyby 193 • INTERACTIVEFIGURE TheMoon’s Synchronous Rotation 195 • ANIMATION/VIDEO FirstSteponthe Moon 198 • ANIMATION/VIDEO Ranger Spacecraft Descent to Moon 199 • INTERACTIVEFIGURE Mercury’s Rotation 200 • INTERACTIVEFIGURE Meteoroid Impact 201 • ANIMATION/VIDEO Protoplanetary Collision 209 • NARRATED FIGURE Moon Formation 211 Chapter 13 Uranus and Neptune 318 • ANIMATION/VIDEO Neptune’sDark Spot 321 • ANIMATION/VIDEO Rotationof Uranus 324 • ANIMATION/VIDEO Rotationof Neptune 325 • INTERACTIVEFIGURE JovianMagnetic Fields 327 • INTERACTIVEFIGURE Jovian Interiors 327 • ANIMATION/VIDEOGeyserson Triton 331 Chapter 11 Jupiter 264 • SELF-GUIDEDTUTORIAL Jupiter— Differential Rotation 267 • ANIMATION/VIDEO Jupiter’s Rotation 268 • INTERACTIVEFIGURE Rotational Flattening 268 • INTERACTIVEFIGURE Zonal Flow 270 • ANIMATION/VIDEO Galileo Mission to Jupiter 272 • ANIMATION/VIDEOCometImpactwith Jupiter 275 • ANIMATION/VIDEO TheGas Giants II 276 Chapter 14 Solar System Debris 338 Chapter 9 Venus 216 • NARRATEDINTERACTIVE InnerSolar System 340 • ANIMATION/VIDEO OrbitingEros 341 • ANIMATION/VIDEO NEAR Descent 341 • NARRATEDFIGURE Venus’s Brightness 218 • SELF-GUIDEDTUTORIAL Super- spaceship—Voyage to Venus 219 xvi

  17. PART THREE: STARS AND STELLAR EVOLUTION • ANIMATION/VIDEO NEAR Landing 341 • ANIMATION/VIDEO SunGrazing Comets 346 • ANIMATION/VIDEO Anatomyofa Comet Part 1 346 • ANIMATION/VIDEO CometHale-Bopp Nucleus Animation 347 • ANIMATION/VIDEO Anatomyofa Comet Part 2 347 • ANIMATION/VIDEO DeepImpact Simulation 352 • INTERACTIVEFIGURE Comet Wild-2 352 • INTERACTIVEFIGURE Deep Impact 352 • ANIMATION/VIDEO OrbitsofNeptune and Pluto 354 • INTERACTIVEFIGURE Neptuneand Pluto 354 • ANIMATION/VIDEO Hubble’s View of Pluto 355 • ANIMATION/VIDEO Historical Observations of Pluto 355 • ANIMATION/VIDEO Asteroid/Comet Breakup 359 • ANIMATION/VIDEO DeltaCapricornid Meteor Near Orion 359 • ANIMATION/VIDEO DaytimePassageof Meteor Fireball 359 • ANIMATION/VIDEO OrionNebula Mosaic 453 • ANIMATION/VIDEO TheTarantula Nebula 454 • INTERACTIVEFIGURE TrifidNebula 454 • ANIMATION/VIDEO GaseousPillarsof Star Birth, the Eagle Nebula 456 • ANIMATION/VIDEOHorsehead Nebula 461 386 Chapter 16 The Sun 388 • SELF-GUIDEDTUTORIAL Super- Spaceship—Voyage to the Sun 390 • NARRATED FIGURE Stellar Balance 392 • ANIMATION/VIDEOSolar Granulation 396 • ANIMATION/VIDEO Solar Chromosphere 399 • ANIMATION/VIDEO Sunspot 401 • ANIMATION/VIDEO SolarFlare 407 • ANIMATION/VIDEO CoronalMass Ejections 407 • INTERACTIVEFIGURE Solar Fusion 412 Chapter 19 Star Formation 468 • ANIMATION/VIDEO StellarBirth 475 • INTERACTIVEFIGURE NewbornStaron theH–RDiagram 476 • ANIMATION/VIDEO BinaryBrown Dwarfs 479 • INTERACTIVEFIGURE OrionNebula,Up Close 481 • ANIMATION/VIDEO Protostars 482 • ANIMATION/VIDEO Herbig–Haro Objects 483 • ANIMATION/VIDEO Bipolar Outflow 483 • ANIMATION/VIDEO TriggeredStar Formation 485 • INTERACTIVEFIGURE Protostellar Collisions 489 • INTERACTIVEFIGURE YoungStarsin Orion 489 • ANIMATION/VIDEO Carina Nebula 490 Chapter 17 The Stars 420 • SELF-GUIDEDTUTORIAL Stellar Parallax 422 • ANIMATION/VIDEO TheInverse-Square Law 425 • NARRATED FIGURE Inverse-Square Law 425 • INTERACTIVEFIGURE Apparent Magnitude 427 • INTERACTIVEFIGURE H–RDiagramof Well-Known Stars 435 • INTERACTIVEFIGURE H–RDiagramof Nearby Stars 435 • ANIMATION/VIDEO WhiteDwarfsin Globular Cluster 436 • SELF-GUIDEDTUTORIAL Hertzsprung– Russell Diagram 436 • SELF-GUIDEDTUTORIAL BinaryStars— Radial Velocity Curves 440 • INTERACTIVEFIGURE Spectroscopic Binary 440 • SELF-GUIDEDTUTORIAL EclipsingBinary Stars—Light Curves 441 • INTERACTIVEFIGURE Eclipsing Binary 441 Chapter 15 Exoplanets 366 • ANIMATION/VIDEO Protoplanetary Disks in the Orion Nebula 369 • ANIMATION/VIDEO ProtoplanetaryDisk Destruction 369 • ANIMATION/VIDEO Evolutionof Protoplanetary Disk 370 • ANIMATION/VIDEO TheFormationof the Solar System 370 • INTERACTIVEFIGURE Planets Revealed 372 • INTERACTIVEFIGURE AnExtrasolar Transit 373 • ANIMATION/VIDEO HotJupiter Extrasolar Planet Evaporating 380 • ANIMATION/VIDEO Surveyfor Transiting Extrasolar Planets 380 • INTERACTIVEFIGURE Jupiter-like Planet? 380 • INTERACTIVEFIGURE Sinking Planet 380 Chapter 20 Stellar Evolution 494 • ANIMATION/VIDEO H–RDiagramTracks Stellar Evolution 498 • ANIMATION/VIDEO RedGiant Evolution 499 • ANIMATION/VIDEO DeathoftheSun Part 1 502 • INTERACTIVEFIGURE G-TypeStar Evolution 502 • ANIMATION/VIDEO DeathoftheSun Part II 503 • ANIMATION/VIDEO HelixNebula Animation 504 • ANIMATION/VIDEO HelixNebula 504 • ANIMATION/VIDEO Bi-PolarPlanetary Nebula 504 • INTERACTIVE FIGURE WhiteDwarfon theH–RDiagram 505 Chapter 18 The Interstellar Medium 448 • ANIMATION/VIDEO PillarsBehindthe Dust 451 • ANIMATION/VIDEO InfraredViewof Nebulae 451 • NARRATEDFIGURE Reddening 451 xvii

  18. • ANIMATION/VIDEO HelixNebula White Dwarf 506 • ANIMATION/VIDEO WhiteDwarf Cooling Sequence 506 • SELF-GUIDEDTUTORIAL Evolution of a 1-Solar-Mass Star 507 • ANIMATION/VIDEO Light Echo 511 • INTERACTIVEFIGURE Gravitational Redshift 563 • ANIMATION/VIDEO BlackHoleand Companion Star 565 • ANIMATION/VIDEO BlackHole Devours Neutron Star 565 • INTERACTIVEFIGURE StellarBlack Hole 567 • ANIMATION/VIDEO Supermassive Black Hole, Black Hole in the Center of M32 569 • ANIMATION/VIDEO BlackHole Accretion Disk and Jets 569 • ANIMATION/VIDEO Active Galaxy 624 • ANIMATION/VIDEO M87 Jet 628 • ANIMATION/VIDEO Eruptionofa Supermassive Black Hole 628 • INTERACTIVE FIGURE M87 Jet 628 Chapter 21 Stellar Explosions 520 Chapter 25 Galaxies and Dark Matter 638 • INTERACTIVEFIGURE Rotation Curve for a Merry-Go-Round 640 • INTERACTIVE FIGURE Galaxy Rotation Curves 640 • ANIMATION/VIDEO Dark Matter 641 • ANIMATION/VIDEO Galaxy Collision 644 • ANIMATION/VIDEO Starburst Galaxy 644 • INTERACTIVE FIGURE Starburst Galaxy 644 • ANIMATION/VIDEO TheEvolutionof Galaxies 647 • ANIMATION/VIDEO HubbleDeep Field Zoom I 647 • ANIMATION/VIDEO HubbleDeep Field Zoom II 647 • ANIMATION/VIDEO Galaxy Merger 650 • NARRATED FIGURE Galaxy Evolution 655 • ANIMATION/VIDEO Cluster Merger 656 • INTERACTIVE FIGURE Absorption Line “Forest” 659 • ANIMATION/VIDEO Howa Gravitational Lens Works 660 • INTERACTIVE FIGURE Gravitational Lens 660 • ANIMATION/VIDEO Simulation of Gravitational Lens in Space 661 • ANIMATION/VIDEO DarkMatter Collision 662 • ANIMATION/VIDEO BulletCluster Collision 662 • INTERACTIVE FIGURE Cluster Collision 662 • ANIMATION/VIDEO Recurrent Nova 523 • INTERACTIVEFIGURE Heavy- Element Fusion 524 • ANIMATION/VIDEO Structureof Supernova 526 • ANIMATION/VIDEO Supernova Explosion 526 • INTERACTIVEFIGURE Crab Supernova Remnant 529 • ANIMATION/VIDEO Supernova Remnant in Cassiopeia 530 • INTERACTIVEFIGURE Vela Supernova Remnant 530 • ANIMATION/VIDEO Composition and Structure of the Ring Around Supernova 1987A 533 • ANIMATION/VIDEO Shockwaves Hit the Ring of Supernova 1987A 533 • INTERACTIVEFIGURE Stellar Recycling 538 PART FOUR: GALAXIES AND COSMOLOGy 574 Chapter 23 The Milky Way Galaxy 576 • ANIMATION/VIDEOCepheidVariable Star in Distant Galaxy 581 • NARRATED FIGURE Globular Cluster Distribution 585 • INTERACTIVEFIGURE Stellar Populations in Our Galaxy 585 • INTERACTIVEFIGURE InfraredView of the Milky Way 587 • INTERACTIVE FIGURE Milky Way Spiral Structure 592 • INTERACTIVE FIGURE Differential Galactic Rotation 593 • INTERACTIVE FIGURE Spiral Density Waves 593 • ANIMATION/VIDEORotating Globular Cluster 597 • SELF-GUIDEDTUTORIAL Gravitational Lensing 598 • INTERACTIVE FIGURE Galactic Center 599 • ANIMATION/VIDEOX-rayViewof Galactic Core 600 • ANIMATION/VIDEOBlackHole in the Center of the Milky Way? 601 Chapter 22 Neutron Stars and Black Holes 542 • NARRATED FIGURE Pulsar Model 546 • ANIMATION/VIDEO PulsarinCrab Nebula 547 • ANIMATION/VIDEO X-rayBinary Star 549 • ANIMATION/VIDEO CollidingBinary Neutron Stars 554 • SELF-GUIDEDTUTORIAL Escape Speed and Black Hole Event Horizons 557 • INTERACTIVEFIGURE Curved Space 560 • ANIMATION/VIDEO Energy Released from a Black Hole? 563 Chapter 24 Galaxies 606 • NARRATED FIGURE Galaxy Rotation 616• • INTERACTIVEFIGURE Spacetime Diagram for an Extragalactic Supernova 623 xviii

  19. Chapter 26 Cosmology 666 Chapter 27 The Early Universe 688 Chapter 28 Life in the Universe 714 • ANIMATION/VIDEO Cosmic Structure 668 • INTERACTIVEFIGURE TheExpanding Raisin Cake (Universe) 672 • INTERACTIVE FIGURE Receding Galaxies 672 • INTERACTIVE FIGURE Cosmological Redshift 673 • ANIMATION/VIDEO TheFirstStars ReionizetheUniverse 696 • INTERACTIVE FIGURE Creation of the Cosmic Microwave Background 699 • ANIMATION/VIDEO CosmicStructure 706 • NARRATED FIGURE Structure Formation 706 • INTERACTIVE FIGURE Early Structure 708 • ANIMATION/VIDEO IcyOrganicsin Planet-Forming Disc 719 • ANIMATION/VIDEO Earth’sBiospherein Action: Plankton Bloom 722 • NARRATED FIGURE Drake Equation 725 • ANIMATION/VIDEO AsteroidImpacting the Earth 728 xix

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  21. About the Authors Steve McMillan Eric Chaisson Steve holds a bachelor’s and master’s degree in math- ematics from Cambridge University and a doctorate in astronomy from Harvard University. He held postdoctoral positions at the University of Illinois and Northwestern University, where he continued his research in theoretical astrophysics, star clusters, and high-performance comput- ing. Steve is currently Distinguished Professor of Physics at Drexel University and a frequent visiting researcher at Princeton’s Institute for Advanced Study and Leiden University. He has published more than 100 articles and scientific papers in professional journals. Eric holds a doctorate in astrophysics from Harvard University, where he spent 10 years on the faculty of Arts and Sciences. For more than two decades there- after, he served on the senior science staff at the Space Telescope Science Institute and held various profes- sorships at Johns Hopkins and Tufts universities. He is now back at Harvard, where he teaches and con- ducts research at the Harvard-Smithsonian Center for Astrophysics. Eric has written 12 books on astronomy and has published nearly 200 scientific papers in pro- fessional journals. xxi

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  23. Preface Astronomy is a science that thrives on new discoveries. Fueled by new technologies and novel theoretical insights, the study of the cosmos continues to change our understanding of the universe. We are pleased to have the opportunity to present in this book a representative sample of the known facts, evolving ideas, and frontier discoveries in astronomy today. Astronomy Today has been written for students who have taken no previous college science courses and who will likely not major in physics or astronomy. It is intended for use in a one- or two-semester, nontechnical astronomy course. We present a broad view of astronomy, straightfor- wardly descriptive and without complex mathematics. The absence of sophisticated mathematics, however, in no way prevents discussion of important concepts. Rather, we rely on qualitative reasoning as well as analogies with objects and phenomena familiar to the student to explain the complexi- ties of the subject without oversimplification. We have tried to communicate the excitement we feel about astronomy and to awaken students to the marvelous universe around us. We are very gratified that the first seven editions of this text have been so well received by many in the astronomy education community. In using those earlier texts, many teachers and students have given us helpful feedback and constructive criticisms. From these, we have learned to com- municate better both the fundamentals and the excitement of astronomy. Many improvements inspired by these comments have been incorporated into this new edition. spectrum of astronomical research. Almost every chapter in the eighth edition has been substantially updated with new information. Several chapters have also seen significant reorganization in order to streamline the overall presentation, strengthen our focus on the process of science, and reflect new understanding and emphases in contemporary astronomy. In addition to updates throughout the text on the num- bers and properties of the many astronomical objects, the many substantive changes include the following: l A new Discovery box in Chapter 5 on the ALMA inter- ferometric array. l Significant revision in Chapter 5 of the discussion of infrared telescopes, including new coverage of Herschel and introduction of the James Webb Space Telescope. l A new two-page box in Chapter 6 on planetary exploration. l Incorporation and reorganization of the entire “standard” theory of solar system formation into Chapter 6, laying the groundwork for interpreting the planetary data presented in Part 2 and allowing Chapter 15 to focus on solar system details, irregularities, and exoplanets. l Updated discussion in Discovery 8-1 of Chang’e, GRAIL, and other recent lunar missions; new discussion of the Prospector, LRO, and LCROSS missions, with updated coverage of the search for lunar ice. l Updated coverage in Chapter 8 of the lunar core and interior based on the latest GRAIL results. l Updated discussion in Chapter 8 of surface features on Mercury, following the Messenger mission. l Updated discussion in Chapter 8 of Mercury’s inner and outer core and magnetic field and formation, in light of new Messenger data. l Updated discussion in Chapter 9 of Venus Express find- ings and status. l Updated discussion in Chapter 10 of the collision hypoth- esis as the origin of the northern Martian lowlands. l Reorganized and updated discussion in Chapter 10 of liquid water on the Martian surface. l Updated discussion in Chapter 10 on the Spirit, Opportunity, and Phoenix landers; new material on the Curiosity lander and its findings. l Revised discussion in Chapter 10 of the origin of the Martian moons. l Updated coverage of cometary impacts in Discovery 11-1, indicating that such impacts are commonplace in the solar system. Focus of the Eighth Edition From the first edition, we have tried to meet the challenge of writing a book that is both accurate and approachable. To the student, astronomy sometimes seems like a long list of unfamiliar terms to be memorized and repeated. Many new terms and concepts will be introduced in this course, but we hope students will also learn and remember how science is done, how the universe works, and how things are connected. In the eighth edition, we have taken particular care to show how astronomers know what they know, and to highlight both the scientific principles underlying their work and the process used in discovery. New and Revised Material Astronomy is a rapidly evolving field and, in the three years since the publication of the seventh edition of Astronomy Today, has seen many new discoveries covering the entire xxiii

  24. xxiv Preface The Illustration Program Visualization plays an important role in both the teaching and the practice of astronomy, and we con- tinue to place strong emphasis on this aspect of our book. We have tried to combine aesthetic beauty with scientific accuracy in the art- ist’s conceptions that adorn the text, and we have sought to pre- sent the best and latest imagery of a wide range of cosmic objects. Each illustration has been care- fully crafted to enhance student learning; each is pedagogically sound and tied tightly to the nearby discus- sion of important scientific facts and ideas. This edition contains more than 100 revised figures that show the latest imagery and the results learned from them. Compound Art It is rare that a single image, be it a pho- tograph or an artist’s conception, can capture all aspects of a complex subject. Wherever possible, multiple-part figures are used in an attempt to convey the greatest amount of information in the most vivid way: Volcano Plume Volcanic plume 1500 km R I V U X G InteractiveFIGURE 11.20 Volcanoes on Io The main image shows a Galileo view of Io, whose surface is kept smooth and brightly colored by constant volcanism, revealed here as dark, circular features. The left inset shows an umbrella-like eruption of one of Io’s volcanoes as Galileo flew past this fascinating moon in 1997; the plume measures about 150 km high and 300 km across. The right inset shows anothervolcano,thisoneface-on,wheresurfacefeatureshereareresolvedtojustafew kilometers. (NASA) Surface Escaping infrared radiation Visible sunlight Refected sunlight Infrared partially absorbed in atmosphere Cloud l Visible images are often presented along with their counter- parts captured at other wavelengths. l Interpretive line drawings are often superimposed on or juxtaposed with real astronomical photographs, helping students to really “see” what the photographs reveal. l Breakouts—often multiple ones—are used to zoom in from wide-field shots to close-ups so that detailed images can be understood in their larger context. Carbon dioxide molecules Earth’s atmosphere Reradiated infrared radiation Sunlight reaches surface Earth’s surface Interactive Figures and Photos Icons through- out the text direct students to dynamic, interactive versions of art and photos on MasteringAstronomy®. Using online applets, students can manipulate factors such as time, wavelength, scale, and perspective to increase their understanding of these figures. Interactive FIGURE 7.5 Greenhouse Effect Sunlight that is not reflected by clouds reaches Earth’s surface, warming it up. Infrared radiation reradiated from the surface is partially absorbed by carbon dioxide (and also water vapor, not shown here) in the atmosphere, causing the overall surface temperature to rise.

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