DISCOVERING THE UN I VERSE SEVENTH EDITION F. COfflifIS University of Maine Willllifli J* KdUftn^nn III San Diego State University W. H, FREEMAN AND COMPANY New York
Preface xiv 30 WHAT IF... Earth's Axis Lay on the Ecliptic? 35 Part 1 UNBEKSTANDING ASTRONOMY [ 1 Discovering the Night Sky SCALES OF THE UNIVERSE 1-1 Astronomical distances are, well, astronomical PATTERNS OF STARS 1:2 Constellations make locating stars easy GUIDED DISCOVERY The Stars and Constellations 1-3 The celestial sphere aids in navigating the sky EARTHLY CYCLES 12 1-4 Earth's rotation creates the day-night cycle and its revolution defines a year 12 AN ASTRONOMER'S TOOLBOX 1-1 Observational Measurements Using Angles 13 1-5 Clock times based on the Sun's location created scheduling nightmares 16 1-6 Calendars based on equal-length years also created scheduling problems 17 1-7 The seasons result from the tilt of the Earth's rotation axis combined with its revolution around the Sun 17 1-8 Precession is a slow, circular motion of the Earth's axis of rotation 21 1-9 The phases of the Moon originally inspired the concept of the month 23 ECLIPSES 25 1-10 Eclipses occur only when the Moon crosses the ecliptic during the new or full phase 25 1-11 There are three types of lunar eclipse 26 1-12 There are also three types of solar eclipse 27 1-13 Frontiers yet to be discovered 30 11 11 D 2 Gravitation and the Waltz of the Planets 36 SCIENCE: KEY TO COMPREHENDING THE COSMOS 38 2-1 Science is both a body of knowledge and a process of learning about nature 38 CHANGING OUR. EARTH-CENTERED VIEW OF THE UNIVERSE 39 2-2 The belief in a Sun-centered cosmology came slowly 39 GUIDED DISCOVERY The Earth-Centered Universe 40 2-3 Copernicus devised the first comprehensive heliocentric cosmology 41 GUIDED DISCOVERY Astronomy's Foundation Builders 43 2-4 Tycho Brahe made astronomical observations that disproved ancient ideas about the heavens 45 KEPLER'S AND NEWTON'S LAWS 46 2-5 Kepler's laws describe orbital shapes, changing speeds, and the lengths of planetary years 46 AN ASTRONOMER'S TOOLBOX 2-1 Astronomical Distances, 49 2-6 Galileo's discoveries strongly supported a heliocentric cosmology 50 2-7 Newton formulated three laws that describe fundamental properties of physical reality 51 AN ASTRONOMER'S TOOLBOX 2-2 Energy and Momentum 53 2-8 Newton's description of gravity accounts for Kepler's laws 55 AN ASTRONOMER'S TOOLBOX 2-3 Gravitational Force. 55 2-9 Frontiers yet to be discovered 57 57
L? THE 3-1 3-2 3-3 3-4 Lignc ana leiescopes NATURE OF LIGHT Newton discovered that white light is not a fundamental color and debated whether light is composed of particles or waves Light travels at a finite, but incredibly fasti speed Einstein showed that light sometimes behaves as particles that carry energy Light is only one type of electromagnetic radiation OPTICS AND TELESCOPES 68 3-5 Reflecting telescopes use mirrors to concentrate incoming starlight 68 3-6 Telescopes brighten, resolve, and magnify 71 3-7 Storing and analyzing light from space is key to understanding the cosmos 73 3-8 Eyepieces, refracting telescopes, binoculars, and eyeglasses use lenses to change the direction of incoming light 73 3-9 Refractors have more limitations than reflectors 76 GUIDED DISCOVERY Buying a Telescope 78 3-10 Earth's atmosphere hinders astronomical research 78 3-11 The Hubble Space Telescope provides stunning details about the universe 81 3-12 Advanced technology is spawning a new generation of superb ground-based telescopes 82 NONOPTICAL ASTRONOMY 83 3-13 A radio telescope uses a large concave dish to reflect radio waves 83 3-14 Infrared and ultraviolet telescopes also use reflectors to collect their electromagnetic radiation 86 3-15 X-ray and gamma-ray telescopes cannot use normal reflectors to gather information 88 3-16 Frontiers yet to be discovered 90 62 63 63 65 67 67 90 What If...Humans Had Infrared-Sensitive Eyes? 94 [4 Visible Light and Other Electromagnetic Radiation 95 BLACKBODY RADIATION 96 4-1 An object's peak color shifts to shorter wavelengths as it is heated 96 4-2 The intensities of different emitted colors reveal a star's temperature 97 AN ASTRONOMER'S TOOLBOX 4-1 The Radiation Laws 98 GUIDED DISCOVERY The Color of the Sun 99 AN ASTRONOMER'S TOOLBOX 4-2 Photon Energies 100 IDENTIFYING THE ELEMENTS BY ANALYZING THEIR UNIQUE SPECTRA 101 4-3 Each chemical element produces its own unique set of spectral lines 102 4-4 The brightnesses of spectral lines depend on conditions in the spectrum's source 105 ATOMS AND SPECTRA 105 4-5 An atom consists of a small, dense nucleus surrounded by electrons 106 AN ASTRONOMER'S TOOLBOX 4-3 Radioactivity and the Ages of Objects 107 4-6 Spectra occur because electrons absorb and emit photons with only certain wavelengths 107 4-7 Spectral lines shift due to the relative motion between the source and the observer 110 AN ASTRONOMER'S TOOLBOX 4-4 The Doppler Shift 111 4-8 Frontiers yet to be discovered 112 112
Part II UNIKANDING THE SOLAR Sitei [ 5 Formation of the Solar System and Other Planetary Systems FORMATION OF THE SOLAR SYSTEM 5-1 The solar system formed from a cloud of cold gas and dust 5-2 Gravity, rotation, and heat shaped the young solar system 5-3 Collisions in the early solar system led to the formation of planets 5-4 Minor debris from the formation of the solar system still exists 118 119 119 121 123 126 COMPARATIVE PLANETOLOGY 127 5-5 Comparisons among the nine planets show distinct similarities and significant differences 127 PLANETS OUTSIDE OUR SOLAR SYSTEM 130 5-6 Planets orbiting other stars have been discovered 130 5-7 Extrasolar planets orbit a breathtaking variety of stars 134 5-8 Frontiers yet to be discovered 134 134 [_6 Earth and Moon 137 EARTH: A DYNAMIC, VITAL WORLD 138 6-1 The Earth's atmosphere has evolved over billions of years 138 6-2 Plate tectonics produce major changes on the Earth's surface 141 6-3 Earth's interior consists of a rocky mantle and an iron-rich core 143 6-4 The Earth's magnetic field shields us from the solar wind 145 THE MOON AND TIDES 148 6-5 The Moon's surface is covered with craters, plains, and mountains 148 6-6 Visits to the Moon yielded invaluable information about its history 152 6-7 The Moon probably formed from debris cast into space when a huge asteroid struck the young Earth 155 6-8 Gravitational force and the orbits of the Moon and Earth produce the tides on Earth and also force the Moon to rotate at the same rate that it revolves around the Earth 157 GUIDED DISCOVERY Tides 6-9 The Moon is moving away from the Earth 6-10 Frontiers yet to be discovered What If... The Moon Didn't Exist? 7 The Other Terrestrial Planets and Their Comparison to Earth MERCURY 7-1 Photographs from Mariner 10 reveal Mercury's lunarlike surface 7-2 More of Mercury's interior is iron than the interior of Earth 7-3 Mercury's rotation and revolution are coupled 7-4 Mercury's atmosphere is the thinnest of all terrestrial planets VENUS 7-5 The surface of Venus is completely hidden beneath a permanent cloud cover GUIDED DISCOVERY The Inner Solar System 7-6 The greenhouse effect heats Venus's surface 158 160 160 161 165 166 167 167 170 171 172 173 173 175 176 7-7 Venus is covered with gently rolling hills, two "continents," and numerous volcanoes 177 MARS 180 7-8 Mars's global features include plains, canyons, craters, and volcanoes 181 7-9 While no canals exist on Mars, it does have small bizarre features 184 7-10 Mars's interior is less molten than the inside of the Earth 184 7-11 Martian air is thin and often filled with dust 185 7-12 Surface features indicate that water once flowed on Mars 188
7-13 Search for microscopic life on Mars continues 191 7-14 Mars has a crust of varying thickness 192 7-15 Mars's two moons look more like potatoes than spheres 193 7-16 Comparisons of planetary features provides new insights 193 7-17 Frontiers yet to be discovered 195 195 fjj The Outer Planets JUPITER 8-1 Jupiter's outer layer is a dynamic area of storms and turbulent gases 8-2 Jupiter's interior has four distinct regions 8-3 Cometary fragments were observed to strike Jupiter JUPITER'S MOONS AND RINGS 8-4 Io's surface is sculpted by volcanic activity 8-5 Europa apparently harbors liquid water below its surface 8-6 Ganymede is larger than Mercury 8-7 Callisto bears the scars of a huge asteroid impact 8-8 Other debris orbits Jupiter as smaller moons and ringlets 200 201 201 205 206 207 209 210 211 212 213 SATURN 214 8-9 Saturn's surface and interior are similar to those of Jupiter 214 8-10 Saturn's spectacular rings are composed of fragments of ice and ice-coated rock 217 8-11 Titan has a thick, opaque atmosphere rich in nitrogen, methane, and other hydrocarbons 220 URANUS 223 8-12 Uranus sports a hazy atmosphere and clouds 223 8-13 A system of rings and satellites revolves around Uranus 225 NEPTUNE 226 8-14 Neptune was discovered because it had to be there 226 8-15 Neptune has rings and has captured most of its moons 228 PLUTO AND BEYOND 229 8-16 Pluto and its moon, Charon, are about the same size 230 8-17 Comparative planetology of the outer planets 232 8-18 Frontiers yet to be discovered 232 234 What If... We Lived on a Metal-poor Earth? 238 9 Vagabonds of the Solar System 239 ASTEROIDS: THE MINOR PLANETS 9-1 Most asteroids orbit the Sun between Mars and Jupiter 9-2 Jupiter's gravity creates gaps in the asteroid belt 9-3 Asteroids exist outside the asteroid belt CO/V 9-4 9-5 9-6 MET 9-7 9-8 9-9 9-10 240 240 242 244 246 Comets come from far out in the solar system 246 Comet tails develop from gases and dust pushed outward by the Sun 249 Comets do not last forever 252 METEOROIDS, METEORS, AND METEORITES 254 Small rocky debris peppers the solar system 254 Impact craters and meteor showers mark remnants of space debris on Earth, while meteorite impacts are seen on the Moon 254 Meteorites are space debris that land intact 257 The Allende meteorite and Tunguska mystery provide evidence of catastrophic collisions 260 9-11 Asteroid impacts with Earth have caused mass extinctions 261 9-12 Frontiers yet to be discovered 263 263 r The Sun: Our Extraordinary IP Ordinary Star 267 THE SUN'S ATMOSPHERE 268 10-1 The photosphere is the visible layer of the Sun 268 10-2 The chromosphere is characterized by spikes of gas called spicules 270 10-3 Temperatures increase higher in the Sun's atmosphere 271
THE ACTIVE SUN 10-4 Sunspots reveal the solar cycle and the Sun's rotation 10-5 The Sun's magnetic fields create sunspots 10-6 Solar magnetic fields also create other atmospheric phenomena 273 273 275 278 THE SUN'S INTERIOR 281 10-7 Thermonuclear reactions in the core of the Sun produce its energy 281 AN ASTRONOMER'S TOOLBOX 10-1 Thermonuclear Fusion 282 10-8 Solar models describe how energy escapes ' from the Sun's core 282 10-9 The mystery of the missing neutrinos inspired research into the fundamental nature of matter 285 10-10 Frontiers yet to be discovered ~ 286 286 P a r t 111 llllmstanding THE STARS Qi Characterizing Stars 292 11-1 Distances to nearby stars are determined by stellar parallax 293 AN ASTRONOMER'S TOOLBOX 11-1 Distances to Nearby Stars 295 GUIDED DISCOVERY Star Names 296 MAGNITUDE SCALES 296 11-2 Apparent magnitude measures the brightness of stars as seen from Earth 296 AN ASTRONOMER'S TOOLBOX 11-2 Details of the Magnitude Scales 298 11-3 Absolute magnitudes and luminosities do not depend on distance 298 AN ASTRONOMER'S TOOLBOX 11-3 The Distance- Magnitude Relationship 300 THE TEMPERATURES OF STARS 300 11-4 A star's color reveals its surface temperature 300 11-5 A star's spectrum also reveals its surface temperature 301 11-6 Stars are classified by their spectra 303 TYPES OF STARS 11-7 The Hertzsprung-Russell diagram identifies distinct groups of stars 11-8 Luminosity classes set the stage for understanding stellar evolution 11-9 A star's spectral type and luminosity class provide a second distance-measuring technique 304 304 305 307 STELLAR MASSES 307 11-10 Binary stars provide information about stellar masses 307 AN ASTRONOMER'S TOOLBOX 11-4 Kepler's Third Law and Stellar Masses 309 11-11 There is a relationship between mass and luminosity for main-sequence stars 309 11-12 The orbital motion of binary stars affects the wavelengths of their spectral lines 310 11-13 Some binary stars eclipse each other 312 11-14 Frontiers yet to be discovered 313 313 [12 The Lives of Stars from Birth Through Middle Age 317 PROTOSTARS AND PRE-MAIN-SEQUENCE STARS 319 12-1 Gas and dust exist between the stars 319 12-2 Supernovae, collisions of interstellar clouds, and starlight trigger new star formation 322 GUIDED DISCOVERY Observing the Nebulae 323 12-3 When a protostar ceases to accumulate mass, it becomes a pre-main-sequence star 325 12-4 The evolutionary track of a pre-main-sequence star depends on its mass 326 GUIDED DISCOVERY Extrasolar Planets and Brown Dwarfs 327 12-5 H II regions harbor young star clusters 328 12-6 Plotting a star cluster on an H-R diagram reveals its age 331 MAIN-SEQUENCE AND GIANT STARS 332 12-7 Stars spend most of their life cycles on the main sequence 332 EVOLUTION OF STARS WITH MASSES BETWEEN O.O8 AND O.4 M 0 333 12-8 Red dwarfs convert essentially their entire mass into helium 333
EARLY AND MIDLIFE EVOLUTION OF STARS WITH MORE THAN 0.4 M Q 334 12-9 When core hydrogen fusion slows down, a main-sequence star with M > 0.4 M 0 becomes a giant 334 12-10 Helium fusion begins at the center of a giant 336 12-11 As stars evolve, their positions on the H-R diagram shift 337 12-12 Globular clusters are bound groups of old stars 338 VARIABLE STARS 340 12-13 A Cepheid pulsates because it is alternately expanding and contracting 340 12-14 Cepheids enable astronomers to estimate vast distances 341 12-15 Mass transfer in close binary systems can produce unusual double stars 342 12-16 Frontiers yet to be discovered 344 345 What If... The Earth Orbited a 1.5 M n Sun? 348 [13 The Deaths of Stars 349 LOW-MASS STARS AND PLANETARY NEBULAE 350 13-1 Lower-mass stars become supergiants before expanding into planetary nebulae 351 13-2 The burned-out core of a low-mass star becomes a white dwarf 353 13-3 White dwarfs in close binary systems can create powerful explosions 354 INTERMEDIATE-MASS STARS, HIGH-MASS STARS, AND SUPERNOVAE 355 13-4 A series of fusion reactions in intermediate-mass and high-mass stars leads to luminous supergiants 356 13-5 Both intermediate-mass and high-mass stars blow apart in violent supernova explosions 357 13-6 Supernovae occur in our Galaxy, among many others 359 13-7 Cosmic rays are not rays at all 360 13-8 Supernova 1987A offered a detailed look at a massive star's death 361 13-9 Accreting white dwarfs in close binary systems can also explode as supernovae 363 NEUTRON STARS AND PULSARS 364 13-10 The cores of many Type II supernovae become neutron stars 364 13-11 A rotating magnetic field explains the pulses from a neutron star 366 13-12 Colliding neutron stars may provide some of the heavy elements in the universe 368 13-13 Binary neutron stars create pulsating X-ray sources 368 13-14 Neutron stars in binary systems can also emit powerful isolated bursts of X rays 370 13-15 There may exist smaller, more exotic stellar remnants composed of quarks 370 13-16 Frontiers yet to be discovered 372 372 What If... A Supernova Exploded Near Earth? 375 [ 4 Black Holes: Matters of Gravity 376 THE RELATIVITY THEORIES 377 14-1 Special relativity changes our conception of space and time 377 14-2 General relativity explains how matter warps spacetime, creating gravitational attraction 379 14-3 Spacetime affects the behavior of light 380 14-4 General relativity predicts the fate of massive star cores black holes 381 INSIDE A BLACK HOLE 381 14-5 Matter in a black hole becomes much simpler than elsewhere in the universe 381 AN ASTRONOMER'S TOOLBOX 14-1 The Sizes of Black Holes 382 14-6 Falling into a black hole is an infinite voyage 384 14-7 Several binary star systems contain black holes 385 GUIDED DISCOVERY Identifying Stellar-Remnant Black Holes 386 14-8 Other black holes range in mass up to billions of solar masses 387 14-9 Black holes and neutron stars in binary systems often create jets of gas 389
GAMMA-RAY BURSTS 14-10 Gamma-ray bursts are the most powerful explosions in the known universe 14-11 Black holes evaporate 14-12 Frontiers yet to be discovered Paft IV.wilsTANDING THE UlMIVERSi [?5 The Milky Way Galaxy DISCOVERING THE MILKY WAY 15-1 Studies of Cepheid variable stars revealed that the Milky Way is only one of many galaxies THE STRUCTURE OF OUR GALAXY AN ASTRONOMER'S TOOLBOX 15-1 Cepheids and Supernovae as Indicators of Distance 15-2 Cepheid variables help us locate our Galaxy's center 15-3 Nonvisible observations help map the galactic disk 15-4 The galactic nucleus is an active, crowded place 15-5 Our Galaxy's disk is surrounded by a spherical halo of stars and other matter 15-6 The Galaxy is rotating MYSTERIES AT THE GALACTIC FRINGES 15-7 Most of the matter in the Galaxy has not yet been identified 15-8 Frontiers yet to be discovered [?6 Galaxies TYPES OF GALAXIES 16-1 The winding of a spiral galaxy's arms is correlated to the size of its nuclear bulge 16-2 Explosions create flocculent spirals and waves create grand design spirals 16-3 Bars of stars run through the nuclear bulges of barred spiral galaxies 16-4 Elliptical galaxies display a wide variety of sizes and masses 16-5 Hubble represented spiral and elliptical galaxies in a tuning fork-shaped diagram 390 390 391 392 393 398 400 400 402 403 404 405 409 410 411 412 412 413 413 417 418 418 421 423 423 424 CLUSTERS AND SUPERCLUSTERS 426 16-6 Galaxies occur in clumps called clusters, which occur in clumps called superclusters 426 16-7 Clusters of galaxies may appear densely or sparsely populated and regular or irregular in shape 428 16-8 Galaxies in a cluster can collide and combine 429 16-9 Galatic halos may account for some dark matter in the universe 433 SUPERCLUSTERS IN MOTION 434 16-10 The redshifts of superclusters indicate that the universe is expanding 434 AN ASTRONOMER'S TOOLBOX 16-1 The Hubble Law 435 GUIDED DISCOVERY The Tully-Fisher Relation and Other Distance-Measuring Techniques 436 16-11 Different techniques determine the expansion of the universe at different distances from Earth 437 16-12 Astonomers are looking back to a time -. when galaxies were first forming 438 16-13 Frontiers yet to be discovered 439 440 What If... The Solar System Were Located Closer to the Center of the Galaxy? 7 Quasars, Active Galaxies, and Other Ultrahigh Energy Sources QUASARS 17-1 Quasars look like stars but have huge redshifts 17-2 A quasar emits a huge amount of energy from a small volume 444 445 446 447 448 ACTIVE GALAXIES 449 17-3 Active galaxies bridge the energy gap between ordinary galaxies and quasars 449 17-4 BL Lacertae objects and blazars are brighter than either quasars or active galaxies 451 17-5 Active galaxies emit twin jets of gas that span galaxies 452 SUPERMASSIVE ENGINES 452 17-6 Supermassive black holes exist at the centers of most galaxies 453 17-7 Jets of matter ejected from around
black holes explain BL Lac objects, quasars, active galaxies, and double radio sources 454 17-8 Gravity focuses light from quasars 457 17-9 Frontiers yet to be discovered 457 457 8 Cosmology THE BIG BANG 18-1 General relativity predicts an expanding (or contracting) universe 18-2 The expansion of the universe creates a Dopplerlike redshift 18-3 The Hubble constant is related to the age of the universe 18-4 Remnants of the initial expansion, the Big Bang, have been detected AN ASTRONOMER'S TOOLBOX 18-1 H o and the Age of the Universe GUIDED DISCOVERY The Expanding Universe 18-5 The universe has two symmetries isotropy and homogeneity 460 461 461 462 462 463 463 464 466 A BRIEF HISTORY OF SPACETIME, MATTER, ENERGY, AND EVERYTHING 467 18-6 All physical forces in nature were unified at first 467 18-7 Equations explain the evolution of the universe even before matter and energy as we know it existed 468 18-8 During the first second, most of the matter and antimatter in the universe annihilated each other 470 18-9 The universe changed from being controlled by radiation to being controlled by matter 471 18-10 Inflation explains why the universe is isotropic and homogeneous 473 18-11 Galaxies formed from huge clouds of primordial gas 473 18-12 Star formation activity determines a galaxy's initial structure 477 THE FATE OF THE UNIVERSE 477 18-13 The average density of matter is one factor that determines the future of the universe 478 18-14 The overall shape of spacetime affects the future of the universe 478 18-15 Dark energy is causing the universe to accelerate outward 480 18-16 Frontiers yet to be discovered 482 482 9 The Search for Extraterrestrial Life 485 19-1 The existence of life depends on chemical and physical properties of matter 486 19-2 Evidence is mounting that life might exist elsewhere in our solar system 489 19-3 Searches under way for advanced civilizations try to detect their radio signals 489 19-4 The Drake equation: How many civilizations are likely to exist in the Milky Way? 491 19-5 Humans have been sending signals into space for more than a century 492 19-6 Frontiers yet to be discovered 494 What If... Life Had Begun on an Older Earth? 494 495 Appendices A Powers-of-Ten Notation B Guidelines for Solving Math Problems and Reading Graphs C Key Formulas D Temperature Scales E Data Tables E-l The Planets: Orbital Data E-2 The Planets: Physical Data E-3 Satellites of the Planets E-4 The Nearest Stars E-5 The Visually Brightest Stars E-6 The Constellations E-7 Some Useful Astronomical Quantities E-8 Some Useful Physical Constants E-9 Common Conversions Between British and Metric Units E-10 Spiral Galaxies and Interacting Galaxies E-ll Mass and Energy Inventory for the Universe F More to Know G Using the Deep Space Explorer and Starry Night Enthusiast CD-ROM Glossary Answers to Computation Questions and Try These Questions in Astronomer's Toolboxes Index A-l A-l A-4 A-5 A-7 A-7 A-7 A-8 A-ll A-12 A-13 A-16 A-16 A-16 A-16 A-17 A-18 A-19 G-l Ans-1 1-1