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Astronomy SENIOR CONTRIBUTING AUTHORS ANDREW FRAKNOI, FOOTHILL COLLEGE DAVID MORRISON, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION SIDNEY C. WOLFF, NATIONAL OPTICAL ASTRONOMY OBSERVATORY (EMERITUS) OpenStax Rice University 6100 Main Street MS-375 Houston, Texas 77005 To learn more about OpenStax, visit https://openstax.org. Individual print copies and bulk orders can be purchased through our website. ©2018 Rice University. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0). 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OpenStax.org TABLE OF CONTENTS Preface 1 1 Science and the Universe: A Brief Tour 11 1.1 The Nature of Astronomy 13 1.2 The Nature of Science 13 1.3 The Laws of Nature 15 1.4 Numbers in Astronomy 15 1.5 Consequences of Light Travel Time 17 1.6 A Tour of the Universe 18 1.7 The Universe on the Large Scale 23 1.8 The Universe of the Very Small 27 1.9 A Conclusion and a Beginning 28 2 Observing the Sky: The Birth of Astronomy 31 2.1 The Sky Above 32 2.2 Ancient Astronomy 42 2.3 Astrology and Astronomy 49 2.4 The Birth of Modern Astronomy 54 3 Orbits and Gravity 69 3.1 The Laws of Planetary Motion 70 3.2 Newton’s Great Synthesis 76 3.3 Newton’s Universal Law of Gravitation 81 3.4 Orbits in the Solar System 85 3.5 Motions of Satellites and Spacecraft 88 3.6 Gravity with More Than Two Bodies 91 4 Earth, Moon, and Sky 103 4.1 Earth and Sky 104 4.2 The Seasons 107 4.3 Keeping Time 114 4.4 The Calendar 117 4.5 Phases and Motions of the Moon 120 4.6 Ocean Tides and the Moon 125 4.7 Eclipses of the Sun and Moon 129 5 Radiation and Spectra 145 5.1 The Behavior of Light 146 5.2 The Electromagnetic Spectrum 153 5.3 Spectroscopy in Astronomy 161 5.4 The Structure of the Atom 166 5.5 Formation of Spectral Lines 172 5.6 The Doppler Effect 176 6 Astronomical Instruments 189 6.1 Telescopes 190 6.2 Telescopes Today 196 6.3 Visible-Light Detectors and Instruments 206 6.4 Radio Telescopes 210 6.5 Observations outside Earth’s Atmosphere 217 6.6 The Future of Large Telescopes 222 7 Other Worlds: An Introduction to the Solar System 233 7.1 Overview of Our Planetary System 234 7.2 Composition and Structure of Planets 246 7.3 Dating Planetary Surfaces 251 7.4 Origin of the Solar System 254 8 Earth as a Planet 265 8.1 The Global Perspective 266 8.2 Earth’s Crust 270 8.3 Earth’s Atmosphere 278 8.4 Life, Chemical Evolution, and Climate Change 283 8.5 Cosmic Influences on the Evolution of Earth 288 9 Cratered Worlds 303 9.1 General Properties of the Moon 303 9.2 The Lunar Surface 310 9.3 Impact Craters 315 9.4 The Origin of the Moon 320 9.5 Mercury 321 10 Earthlike Planets: Venus and Mars 335 10.1 The Nearest Planets: An Overview 335 10.2 The Geology of Venus 342 10.3 The Massive Atmosphere of Venus 347 10.4 The Geology of Mars 350 10.5 Water and Life on Mars 359 10.6 Divergent Planetary Evolution 371 This OpenStax book is available for free at http://cnx.org/content/col11992/1.13 11 The Giant Planets 381 11.1 Exploring the Outer Planets 381 11.2 The Giant Planets 387 11.3 Atmospheres of the Giant Planets 393 12 Rings, Moons, and Pluto 409 12.1 Ring and Moon Systems Introduced 410 12.2 The Galilean Moons of Jupiter 411 12.3 Titan and Triton 420 12.4 Pluto and Charon 425 12.5 Planetary Rings 432 13 Comets and Asteroids: Debris of the Solar System 451 13.1 Asteroids 452 13.2 Asteroids and Planetary Defense 463 13.3 The “Long-Haired” Comets 466 13.4 The Origin and Fate of Comets and Related Objects 476 14 Cosmic Samples and the Origin of the Solar System 493 14.1 Meteors 494 14.2 Meteorites: Stones from Heaven 499 14.3 Formation of the Solar System 504 14.4 Comparison with Other Planetary Systems 510 14.5 Planetary Evolution 515 15 The Sun: A Garden-Variety Star 527 15.1 The Structure and Composition of the Sun 528 15.2 The Solar Cycle 539 15.3 Solar Activity above the Photosphere 544 15.4 Space Weather 548 16 The Sun: A Nuclear Powerhouse 563 16.1 Sources of Sunshine: Thermal and Gravitational Energy 563 16.2 Mass, Energy, and the Theory of Relativity 566 16.3 The Solar Interior: Theory 576 16.4 The Solar Interior: Observations 582 17 Analyzing Starlight 595 17.1 The Brightness of Stars 595 17.2 Colors of Stars 599 17.3 The Spectra of Stars (and Brown Dwarfs) 602 17.4 Using Spectra to Measure Stellar Radius, Composition, and Motion 609 18 The Stars: A Celestial Census 625 18.1 A Stellar Census 625 18.2 Measuring Stellar Masses 629 18.3 Diameters of Stars 636 18.4 The H–R Diagram 641 19 Celestial Distances 659 19.1 Fundamental Units of Distance 659 19.2 Surveying the Stars 663 19.3 Variable Stars: One Key to Cosmic Distances 672 19.4 The H–R Diagram and Cosmic Distances 679 20 Between the Stars: Gas and Dust in Space 691 20.1 The Interstellar Medium 692 20.2 Interstellar Gas 696 20.3 Cosmic Dust 704 20.4 Cosmic Rays 711 20.5 The Life Cycle of Cosmic Material 714 20.6 Interstellar Matter around the Sun 716 21 The Birth of Stars and the Discovery of Planets outside the 727 Solar System 21.1 Star Formation 728 21.2 The H–R Diagram and the Study of Stellar Evolution 737 21.3 Evidence That Planets Form around Other Stars 740 21.4 Planets beyond the Solar System: Search and Discovery 744 21.5 Exoplanets Everywhere: What We Are Learning 753 21.6 New Perspectives on Planet Formation 759 22 Stars from Adolescence to Old Age 771 22.1 Evolution from the Main Sequence to Red Giants 772 22.2 Star Clusters 778 22.3 Checking Out the Theory 782 22.4 Further Evolution of Stars 789 22.5 The Evolution of More Massive Stars 798 This OpenStax book is available for free at http://cnx.org/content/col11992/1.13