Preface XI
Acknowledgments xvii
PART I
Understanding Astronomy 1
CHAPTER 1 Discovering the Night Sky 5
SCALES OF THE UNIVERSE 7
1-1 Astronomical distances are, well, astronomical 7
PATTERNS OF STARS 9
1-2 Well-known constellations make locating more obscure stars and constellations easy 10
1-3 The celestial sphere aids in navigating the sky 11
GUIDED DISCOVERY The Stars and Constellations 13
1-4 An “alt”ernative coordinate system 13
1-5 Earth orbits the Sun in a plane called the ecliptic 14
AN ASTRONOMER’S TOOLBOX 1-1 Observational Measurements Using Angles 15
EARTHLY CYCLES 16
1-6 Earth’s rotation creates the day-night cycle and its revolution defines a year 16
1-7 The seasons result from the tilt of Earth’s rotation axis combined with Earth’s revolution around the Sun 19
1-8 Clock times based on the Sun’s location created scheduling nightmares 22
1-9 Calendars based on equal-length years also created scheduling problems 24
1-10 Precession is a slow, circular motion of Earth’s axis of rotation 24
1-11 The phases of the Moon originally inspired the concept of the month 26
ECLIPSES 28
1-12 Eclipses do not occur during every new or full Moon phase 28
1-13 Three types of lunar eclipse occur 28
1-14 Three types of solar eclipse also occur 30
1-15 Frontiers yet to be discovered 33
Summary of Key Ideas 33
WHAT IF… Earth’s Axis Lay on the Ecliptic? 40
CHAPTER 2 Gravitation and the Motion of the Planets 41
SCIENCE: KEY TO COMPREHENDING THE COSMOS 42
2-1 Science is both a body of knowledge and a process of learning about nature 43
CHANGING OUR EARTH-CENTERED VIEW OF THE UNIVERSE 45
2-2 The belief in a Sun-centered cosmology formed slowly 45
GUIDED DISCOVERY Earth-Centered Universe 46
2-3 Copernicus devised the first comprehensive heliocentric cosmology 48
GUIDED DISCOVERY Astronomy’s Foundation Builders 49
2-4 Tycho Brahe made astronomical observations that disproved ancient ideas about the heavens 51
KEPLER’S AND NEWTON’S LAWS 52
2-5 Kepler’s laws describe orbital shapes, changing speeds, and the lengths of planetary years 53
AN ASTRONOMER’S TOOLBOX 2-1 Units of Astronomical Distance 55
2-6 Galileo’s discoveries strongly supported a heliocentric cosmology 56
2-7 Newton formulated three laws that describe fundamental properties of physical reality 58
AN ASTRONOMER’S TOOLBOX 2-2 Energy and Momentum 60
2-8 Newton’s description of gravity accounts for Kepler’s laws 60
AN ASTRONOMER’S TOOLBOX 2-3 Gravitational Force 62
2-9 Frontiers yet to be discovered 63
Summary of Key Ideas 65
CHAPTER 3 Light and Telescopes 69
THE NATURE OF LIGHT 70
3-1 Newton discovered that white is not a fundamental color and proposed that light is composed of particles 70
3-2 Light travels at a finite but incredibly fast speed 73
3-3 Einstein showed that light sometimes behaves as particles that carry energy 74
AN ASTRONOMER’S TOOLBOX 3-1 Photon Energies, Wavelengths, and Frequencies 74
3-4 Visible light is only one type of electromagnetic radiation 75
OPTICS AND TELESCOPES 70
3-5 Reflecting telescopes use mirrors to concentrate incoming starlight 77
3-6 Secondary mirrors dim objects but do not create holes in them 79
3-7 Telescopes brighten, resolve, and magnify 80
3-8 Eyepieces, refracting telescopes, and binoculars use lenses to focus incoming light 82
3-9 Shaping telescope mirrors and lenses is an evolving science 86
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3-10Storing and analyzing light from space is key to understanding the cosmos 87
3-11 Earth’s atmosphere hinders astronomical research 88
3-12 The Hubble Space Telescope provides stunning details about the universe 90
3-13 Advanced technology is spawning a new generation of superb ground-based telescopes 90
NONOPTICAL ASTRONOMY 92
3-14 A radio telescope uses a large concave dish to collect radio waves 92
3-15 Infrared and ultraviolet telescopes also use reflectors to collect their electromagnetic radiation 94
3-16 X-ray and gamma-ray telescopes cannot use normal reflectors to gather information 97
3-17 Frontiers yet to be discovered 100
Summary of Key Ideas 100
WHAT IF… Humans Had Infrared-Sensitive Eyes? 104
CHAPTER 4 Atomic Physics and Spectra 105
BLACKBODY RADIATION 106
4-1 An object’s peak color shifts to shorter wavelengths as it is heated 106
4-2 The intensities of different emitted colors reveal a star’s temperature 108
AN ASTRONOMER’S TOOLBOX 4-1 The Radiation Laws 109
GUIDED DISCOVERY The Color of the Sun 110
IDENTIFYING THE ELEMENTS BY ANALYZING THEIR UNIQUE SPECTRA 111
4-3 Each chemical element produces its own unique set of spectral lines 112
4-4 The various brightness levels of spectral lines depend on conditions in the spectrum’s source 114
ATOMS AND SPECTRA 116
4-5 An atom consists of a small, dense nucleus surrounded by electrons 116
4-6 Spectra occur because electrons absorb and emit photons with only certain wavelengths 117
AN ASTRONOMER’S TOOLBOX 4-2 Radioactivity and the Ages of Objects 118
4-7 Spectral lines shift due to the relative motion between the source and the observer 121
AN ASTRONOMER’S TOOLBOX 4-3 The Doppler Shift 121
4-8 Frontiers yet to be discovered 123
Summary of Key Ideas 123
PART II
Understanding the Solar System 127
CHAPTER 5 Formation of the Solar System and Other Planetary Systems 131
THE SOLAR SYSTEM CONTAINS HEAVY ELEMENTS, FORMED FROM AN EARLIER GENERATION OF STARS 132
5-1 Stars transform matter from lighter elements into heavier ones 132
5-2 Gravity, rotation, collisions, and heat shaped the young solar system 134
5-3 The giant planets formed in sequence 137
5-4 The inner planets formed primarily from collisions 138
5-5 The changing orbits of the giant planets spread debris throughout the solar system 139
5-6 The asteroid belt is leftover debris 141
5-7 The infalling debris from the giant planets led to the Late Heavy Bombardment 141
5-8 The categories of solar system objects have evolved 142
5-9 The Sun developed while the planets matured 143
COMPARATIVE PLANETOLOGY 144
5-10 Comparisons among the eight planets show distinct similarities and significant differences 144
EXOPLANETS—PLANETS OUTSIDE OUR SOLAR SYSTEM 147
5-11 Planets and smaller debris that orbit other stars have been discovered 147
5-12 Exoplanets orbit a breathtaking variety of stars 152
5-13 Planets that are not orbiting stars have also been observed 153
5-14 Frontiers yet to be discovered 153
Summary of Key Ideas 154
CHAPTER 6 Earth and the Moon 157
EARTH: A DYNAMIC, VITAL WORLD 158
6-1 Earth’s atmosphere has evolved over billions of years 158
6-2 Plate tectonics produce major changes on Earth’s surface 163
6-3 Earth’s interior consists of a rocky mantle and an iron-rich core 165
6-4 Earth’s magnetic field shields us from the solar wind 168
THE MOON AND TIDES 170
6-5 The Moon’s surface is covered with craters, plains, and mountains 171
6-6 Visits to the Moon yielded invaluable information about its history 174
6-7 The Moon probably formed from debris cast into space when a huge planetesimal struck the young Earth 179
6-8 Tides have played several important roles in the history of Earth and the Moon 181
6-9 The Moon is moving away from Earth 183
GUIDED DISCOVERY Tides 184
6-10 Frontiers yet to be discovered 186
Summary of Key Ideas 186
WHAT IF… The Moon Didn’t Exist? 191
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CHAPTER 7 The Other Terrestrial Planets 193
MERCURY 195
7-1 Photographs from Mariner 10 and Messenger spacecraft reveal Mercury’s lunarlike surface 195
7-2 Mercury has a higher percentage of iron than Earth 198
7-3 Mercury’s rotation and revolution are coupled 199
7-4 Mercury’s atmosphere is the thinnest of all terrestrial planets 201
VENUS 201
7-5 The surface of Venus is completely hidden beneath a permanent cloud cover 201
GUIDED DISCOVERY The Inner Solar System 203
7-6 The greenhouse effect heats Venus’s surface 204
7-7 Venus is covered with gently rolling hills, two “continents,” and numerous volcanoes 205
MARS 208
7-8 Mars’s global features include plains, canyons, craters, and volcanoes 209
7-9 Although no canals exist on Mars, it does have some curious natural features 212
7-10 Mars’s interior is less molten than the inside of Earth 213
7-11 Martian air is thin and often filled with dust 215
7-12 Surface and underground features indicate that water once flowed on Mars 218
7-13 Search for microscopic life on Mars continues 222
7-14 Mars’s two moons look more like potatoes than spheres 223
COMPARATIVE PLANETOLOGY OF THE INNER PLANETS 224
7-15 Comparisons of planetary features provide new insights 224
7-16 Frontiers yet to be discovered 226
Summary of Key Ideas 227
CHAPTER 8 The Outer Planets 231
JUPITER 233
8-1 Jupiter’s outer layer is a dynamic area of storms and turbulent gases 233
8-2 Jupiter’s interior has four distinct regions 236
8-3 Impacts provide probes into Jupiter’s atmosphere 238
JUPITER’S MOONS AND RINGS 239
8-4 Io’s surface is sculpted by volcanic activity 240
8-5 Europa harbors liquid water below its surface 242
8-6 Ganymede is larger than Mercury 244
8-7 Callisto bears the scars of a huge asteroid impact 245
8-8 Other debris orbits Jupiter as smaller moons and ringlets 246
SATURN 247
8-9 Saturn’s atmosphere, surface, and interior are similar to those of Jupiter 247
8-10 Saturn’s spectacular rings are composed of fragments of ice and ice-coated rock 250
8-11 Titan has a thick atmosphere, clouds, and lakes filled with liquids 255
8-12 Rhea has ice 258
8-13 Enceladus has water jets, an atmosphere, and a magnetic field 258
URANUS 259
8-14 Uranus sports a hazy atmosphere and clouds 259
8-15 A system of rings and satellites revolves around Uranus 262
NEPTUNE 264
8-16 Neptune was discovered because it had to be there 265
8-17 Neptune has rings and captured moons 266
COMPARATIVE PLANETOLOGY OF THE OUTER PLANETS 267
8-18 Frontiers yet to be discovered 269
Summary of Key Ideas 269
WHAT IF… We Lived on a Metal-Poor Earth? 274
CHAPTER 9 Vagabonds of the Solar System 275
DWARF PLANETS 276
9-1 Pluto and its moon, Charon, are about the same size 276
9-2 Ceres is a dwarf planet in the asteroid belt, while Pluto, Eris, Haumea, and Makemake are trans-Neptunian objects as well as dwarf planets 279
SMALL SOLAR SYSTEM BODIES 280
ASTEROIDS 280
9-3 Most asteroids orbit the Sun between Mars and Jupiter 280
9-4 Jupiter’s gravity creates gaps in the asteroid belt 283
9-5 Asteroids also orbit outside the asteroid belt 285
COMETS 286
9-6 Comets come from far out in the solar system 287
9-7 Comet tails develop from gases and dust pushed outward by the Sun 290
9-8 Comets are fragile yet durable 293
9-9 Comets do not last forever 293
METEOROIDS, METEORS, AND METEORITES 297
9-10 Small, rocky debris peppers the solar system 297
9-11 Meteorites are space debris that land intact 300
9-12 The Allende meteorite provides evidence of catastrophic explosions 303
9-13 Asteroid impacts with Earth have caused mass extinctions 304
9-14 Frontiers yet to be discovered 305
Summary of Key Ideas 306
CHAPTER 10 The Sun: Our Extraordinary Ordinary Star 311
THE SUN’S ATMOSPHERE 313
10-1 The photosphere is the visible layer of the Sun 313
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10-2 The chromosphere is characterized by spikes of gas called spicules 314
10-3 The outermost layer of the Sun’s atmosphere, the corona, is exceptionally hot 315
THE ACTIVE SUN 317
10-4 Sunspots reveal the solar cycle and the Sun’s rotation 317
10-5 The Sun’s magnetic fields create sunspots 319
10-6 Solar magnetic fields also create other atmospheric phenomena 323
THE SUN’S INTERIOR 326
10-7 Thermonuclear reactions in the core of the Sun produce its energy 326
AN ASTRONOMER’S TOOLBOX 10-1 Thermonuclear Fusion 327
10-8 The solar model describes how energy escapes from the Sun’s core 329
10-9 The Sun has gotten brighter over time 331
10-10 The mystery of the missing neutrinos inspired research into the fundamental nature of matter 331
10-11 Frontiers yet to be discovered 333
Summary of Key Ideas 334
PART III
Understanding the Stars 337
CHAPTER 11 Characterizing Stars 341
11-1 Distances to nearby stars are found using stellar parallax 342
AN ASTRONOMER’S TOOLBOX 11-1 Distances to Nearby Stars 344
MAGNITUDE SCALES 345
11-2 Apparent magnitude measures the brightness of stars as seen from Earth 345
AN ASTRONOMER’S TOOLBOX 11-2 Details of the Magnitude Scales 345
11-3 Absolute magnitudes and luminosities do not depend on distance 347
GUIDED DISCOVERY Star Names 348
AN ASTRONOMER’S TOOLBOX 11-3 The Distance-Magnitude Relationship 349
THE TEMPERATURES OF STARS 349
11-4 A star’s color reveals its surface temperature 349
11-5 A star’s spectrum also reveals its surface temperature 350
11-6 Stars are classified by their spectra 352
TYPES OF STARS 353
11-7 The Hertzsprung-Russell diagram identifies distinct groups of stars 353
11-8 Luminosity classes set the stage for understanding stellar evolution 355
11-9 A star’s spectral type and luminosity class provide a second distance-measuring technique 356
STELLAR MASSES 356
AN ASTRONOMER’S TOOLBOX 11-4 Kepler’s Third Law and Stellar Masses 357
11-10 Binary stars provide information about stellar masses 357
11-11 Main-sequence stars have a relationship between mass and luminosity 360
11-12 The orbital motion of binary stars affects the wavelengths of their spectral lines 361
11-13 Frontiers yet to be discovered 362
Summary of Key Ideas 363
CHAPTER 12 The Lives of Stars from Birth Through Middle Age 369
PROTOSTARS AND PRE–MAIN-SEQUENCE STARS 370
12-1 Gas and dust exist between the stars 370
12-2 Supernovae, collisions of interstellar clouds, and starlight trigger new star formation 374
GUIDED DISCOVERY Observing the Nebulae 375
12-3 When a protostar ceases to accumulate mass, it becomes a pre–main-sequence star 377
12-4 The evolutionary track of a pre–main-sequence star depends on its mass 378
GUIDED DISCOVERY Extrasolar Planets and Brown Dwarfs 379
12-5 H II regions harbor young star clusters 381
12-6 Plotting a star cluster on an H-R diagram reveals its age 382
MAIN-SEQUENCE AND GIANT STARS 384
12-7 Stars spend most of their lives on the main sequence 384
EVOLUTION OF STARS WITH MASSES BETWEEN 0.08 M⊙ AND 0.4 M⊙ 386
12-8 Red dwarfs convert essentially their entire mass into helium 386
EARLY AND MIDDLE EVOLUTION OF STARS WITH MORE THAN 0.4 M⊙ 387
12-9 When core hydrogen fusion slows down, a main-sequence star with mass greater than 0.4 M⊙ becomes a giant 387
12-10 Helium fusion begins at the center of a giant 389
12-11 Life in the giant phase has its ups and downs 390
VARIABLE STARS 390
12-12 A Cepheid pulsates because it is alternately expanding and contracting 391
12-13 Cepheids enable astronomers to estimate vast distances 392
12-14 Globular clusters are bound groups of old stars 392
12-15 Mass transfer in close binary systems can produce unusual double stars 396
12-16 Frontiers yet to be discovered 398
Summary of Key Ideas 399
WHAT IF… Earth Orbited a 1.5-M⊙ Sun? 404
CHAPTER 13 The Deaths of Stars 405
LOW-MASS (0.4 M⊙–8 M⊙) STARS AND PLANETARY NEBULAE 406
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13-1 Low-mass stars become supergiants before expanding into planetary nebulae 407
13-2 The burned-out core of a low-mass star becomes a white dwarf 410
13-3 White dwarfs in close binary systems can create powerful explosions 410
13-4 Accreting white dwarfs in close binary systems can also explode as Type Ia supernovae 411
HIGH-MASS (GREATER THAN 8 M⊙) STARS AND TYPE II SUPERNOVAE 412
13-5 A series of fusion reactions in highmass stars leads to luminous supergiants 413
13-6 High-mass stars blow apart in Type II supernova explosions 414
13-7 Supernova remnants are observed in many places 416
13-8 Supernova 1987A offered a detailed look at a massive star’s death 417
13-9 Cosmic rays are not rays at all 419
NEUTRON STARS AND PULSARS 420
13-10 The cores of many Type II supernovae become neutron stars 420
13-11 A rotating magnetic field explains the pulses from a neutron star 421
13-12 Rotating neutron stars create other phenomena besides normal pulsars 424
13-13 Neutron stars have internal structure 424
13-14 Some pulsars are in binary systems 425
13-15 Colliding neutron stars may provide some of the heavy elements in the universe 426
13-16 Binary neutron stars create pulsating X-ray sources 426
13-17 Neutron stars in binary systems can also emit powerful isolated bursts of X-rays 427
13-18 Frontiers yet to be discovered 429
Summary of Key Ideas 429
WHAT IF… A Supernova Exploded Near Earth? 433
CHAPTER 14 Black Holes: Matters of Gravity 435
THE RELATIVITY THEORIES 436
14-1 Special relativity changes our conception of space and time 436
14-2 General relativity explains how matter warps spacetime, creating gravitational attraction 438
14-3 Spacetime affects the behavior of light 439
14-4 General relativity predicts the fate of massive star cores—black holes 440
INSIDE A BLACK HOLE 440
14-5 Matter in a black hole becomes much simpler than elsewhere in the universe 441
AN ASTRONOMER’S TOOLBOX 14-1 The Sizes of Black Holes 441
14-6 Falling into a black hole is an infinite voyage 443
EVIDENCE FOR BLACK HOLES 444
14-7 Several binary star systems contain black holes 444
14-8 Other black holes range in mass up to billions of solar masses 445
GUIDED DISCOVERY Identifying Stellar-Remnant Black Holes 446
14-9 Black holes and neutron stars in binary systems often create jets of gas 449
GAMMA-RAY BURSTS 449
14-10 Gamma-ray bursts are the most powerful explosions in the known universe 449
14-11 Black holes evaporate 451
14-12 Frontiers yet to be discovered 452
Summary of Key Ideas 453
PART IV
Understanding the Universe 457
CHAPTER 15 The Milky Way Galaxy 461
DEFINING THE MILKY WAY 463
15-1 Studies of Cepheid variable stars revealed that the Milky Way is only one of many galaxies 463
AN ASTRONOMER’S TOOLBOX 15-1 Cepheids and Supernovae as Indicators of Distance 465
THE STRUCTURE OF OUR GALAXY AND OUR PLACE IN IT 466
15-2 Cepheid variables help us locate our Galaxy’s center 466
15-3 Nonvisible observations help map the galactic disk 467
15-4 The galactic nucleus is an active, crowded place 471
15-5 Our Galaxy’s disk is surrounded by a two-shell spherical halo of stars and other matter 473
15-6 The Galaxy is rotating 474
MYSTERIES AT THE GALACTIC FRINGES 476
15-7 Most of the matter in the Galaxy has not yet been identified 476
15-8 Frontiers yet to be discovered 476
Summary of Key Ideas 477
CHAPTER 16 Galaxies 481
TYPES OF GALAXIES 482
16-1 The winding of a spiral galaxy’s arms is correlated to the size of its central bulge 482
16-2 Explosions create flocculent spirals, and waves create grand-design spirals 484
16-3 Bars of stars run through the central bulges of barred spiral galaxies, and some disk galaxies, the lenticulars, lack spiral arms 488
16-4 Elliptical galaxies display a wide variety of sizes and masses 488
16-5 Galaxies without global structure are called irregular 490
16-6 Hubble presented spiral and elliptical galaxies in a tuning fork-shaped diagram 491
16-7 Galaxies built up in size over time 491
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CLUSTERS AND SUPERCLUSTERS 492
16-8 Galaxies exist in clusters, which are clustered in larger clumps called superclusters 492
16-9 Clusters of galaxies may appear densely or sparsely populated and regular or irregular in shape 494
16-10 Galaxies in a cluster can collide and combine 495
16-11 Dark matter helps hold together individual galaxies and clusters of galaxies 500
SUPERCLUSTERS IN MOTION 502
16-12 The redshifts of superclusters indicate that the universe is indeed expanding 502
GUIDED DISCOVERY The Expanding Universe 504
AN ASTRONOMER’S TOOLBOX 16-1 The Hubble Law 505
16-13 Astronomers are looking back to a time when galaxies were first forming 505
GUIDED DISCOVERY The Tully–Fisher Relation and Other Distance-Measuring Techniques 506
16-14 Frontiers yet to be discovered 506
Summary of Key Ideas 507
WHAT IF… The Solar System Were Located Closer to the Center of the Galaxy? 512
CHAPTER 17 Quasars and Other Active Galaxies 513
QUASARS 514
17-1 Quasars look like stars but have huge redshifts 515
17-2 A quasar emits a huge amount of energy from a small volume 517
OTHER ACTIVE GALAXIES 518
17-3 Active galaxies can be either spiral or elliptical 518
SUPERMASSIVE ENGINES 521
17-4 Supermassive black holes exist at the centers of most galaxies 521
17-5 Jets of protons and electrons ejected from around black holes help explain active galaxies 523
17-6 Gravity focuses light from quasars 526
17-7 Frontiers yet to be discovered 526
Summary of Key Ideas 526
CHAPTER 18 Cosmology 529
THE BIG BANG 530
18-1 General relativity predicts an expanding (or contracting) universe 530
18-2 The expansion of the universe creates a Dopplerlike redshift 531
18-3 The Hubble constant is related to the age of the universe 531
AN ASTRONOMER’S TOOLBOX 18-1 H0 and the Age of the Universe 532
18-4 Remnants of the Big Bang have been detected 532
18-5 The universe has two symmetries—isotropy and homogeneity 534
A BRIEF HISTORY OF SPACETIME, MATTER, ENERGY, AND EVERYTHING 535
18-6 All physical forces in nature were initially unified 536
18-7 Equations explain the evolution of the universe, even before matter and energy, as we know them, existed 536
18-8 Homogeneity and isotropy are results of inflation 538
18-9 During the first second, most of the matter and antimatter in the universe annihilated each other 539
18-10 The universe changed from being controlled by radiation to being controlled by matter 540
18-11 Galaxies formed from huge clouds of primordial gas 542
18-12 Star formation activity determines a galaxy’s initial structure 545
THE FATE OF THE UNIVERSE 547
18-13 The average density of matter is one factor that determines the future of the universe 547
18-14 The overall shape of spacetime affects the future of the universe 548
18-15 Dark energy is causing the universe to accelerate outward 549
GUIDED DISCOVERY Superstring Theory and M-Theory 552
18-16 Frontiers yet to be discovered 553
Summary of Key Ideas 553
CHAPTER 19 Astrobiology 557
19-1 Astrobiology connects the cosmos and the origins of life 558
19-2 The existence of life depends on chemical and physical properties of matter 559
19-3 Evidence is mounting that life might exist elsewhere in our solar system 562
19-4 Searches for advanced civilizations try to detect their radio signals 562
19-5 The Drake equation: How many civilizations are likely to exist in the Milky Way? 565
19-6 Humans have been sending signals into space for more than a century 566
19-7 Frontiers yet to be discovered 567
Summary of Key Ideas 568
APPENDICES
A Powers-of-Ten Notation A-1
B Guidelines for Solving Math Problems and Reading Graphs A-1
C Key Formulas A-4
D Temperature Scales A-5
E Data Tables A-7
F Periodic Table of the Elements A-17
G Largest Optical Telescopes in the World A-18
H Buying a Telescope A-20
Glossary G-1
Answers to Selected Questions ANS-1
Index I-0
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