DISCOVERING THE UN I VERSE SEVENTH EDITION. Willllifli J* KdUftn^nn III San Diego State University. F. COfflifIS University of Maine

Transcription

1 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

2 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 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 Clock times based on the Sun's location created scheduling nightmares Calendars based on equal-length years also created scheduling problems The seasons result from the tilt of the Earth's rotation axis combined with its revolution around the Sun Precession is a slow, circular motion of the Earth's axis of rotation The phases of the Moon originally inspired the concept of the month 23 ECLIPSES Eclipses occur only when the Moon crosses the ecliptic during the new or full phase There are three types of lunar eclipse There are also three types of solar eclipse Frontiers yet to be discovered D 2 Gravitation and the Waltz of the Planets 36 SCIENCE: KEY TO COMPREHENDING THE COSMOS Science is both a body of knowledge and a process of learning about nature 38 CHANGING OUR. EARTH-CENTERED VIEW OF THE UNIVERSE The belief in a Sun-centered cosmology came slowly 39 GUIDED DISCOVERY The Earth-Centered Universe Copernicus devised the first comprehensive heliocentric cosmology 41 GUIDED DISCOVERY Astronomy's Foundation Builders Tycho Brahe made astronomical observations that disproved ancient ideas about the heavens 45 KEPLER'S AND NEWTON'S LAWS Kepler's laws describe orbital shapes, changing speeds, and the lengths of planetary years 46 AN ASTRONOMER'S TOOLBOX 2-1 Astronomical Distances, Galileo's discoveries strongly supported a heliocentric cosmology Newton formulated three laws that describe fundamental properties of physical reality 51 AN ASTRONOMER'S TOOLBOX 2-2 Energy and Momentum Newton's description of gravity accounts for Kepler's laws 55 AN ASTRONOMER'S TOOLBOX 2-3 Gravitational Force Frontiers yet to be discovered 57 57

3 L? THE 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 Reflecting telescopes use mirrors to concentrate incoming starlight Telescopes brighten, resolve, and magnify Storing and analyzing light from space is key to understanding the cosmos Eyepieces, refracting telescopes, binoculars, and eyeglasses use lenses to change the direction of incoming light Refractors have more limitations than reflectors 76 GUIDED DISCOVERY Buying a Telescope Earth's atmosphere hinders astronomical research The Hubble Space Telescope provides stunning details about the universe Advanced technology is spawning a new generation of superb ground-based telescopes 82 NONOPTICAL ASTRONOMY A radio telescope uses a large concave dish to reflect radio waves Infrared and ultraviolet telescopes also use reflectors to collect their electromagnetic radiation X-ray and gamma-ray telescopes cannot use normal reflectors to gather information Frontiers yet to be discovered What If...Humans Had Infrared-Sensitive Eyes? 94 [4 Visible Light and Other Electromagnetic Radiation 95 BLACKBODY RADIATION An object's peak color shifts to shorter wavelengths as it is heated 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 Each chemical element produces its own unique set of spectral lines The brightnesses of spectral lines depend on conditions in the spectrum's source 105 ATOMS AND SPECTRA An atom consists of a small, dense nucleus surrounded by electrons 106 AN ASTRONOMER'S TOOLBOX 4-3 Radioactivity and the Ages of Objects Spectra occur because electrons absorb and emit photons with only certain wavelengths Spectral lines shift due to the relative motion between the source and the observer 110 AN ASTRONOMER'S TOOLBOX 4-4 The Doppler Shift Frontiers yet to be discovered

4 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 COMPARATIVE PLANETOLOGY Comparisons among the nine planets show distinct similarities and significant differences 127 PLANETS OUTSIDE OUR SOLAR SYSTEM Planets orbiting other stars have been discovered Extrasolar planets orbit a breathtaking variety of stars Frontiers yet to be discovered [_6 Earth and Moon 137 EARTH: A DYNAMIC, VITAL WORLD The Earth's atmosphere has evolved over billions of years Plate tectonics produce major changes on the Earth's surface Earth's interior consists of a rocky mantle and an iron-rich core The Earth's magnetic field shields us from the solar wind 145 THE MOON AND TIDES The Moon's surface is covered with craters, plains, and mountains Visits to the Moon yielded invaluable information about its history The Moon probably formed from debris cast into space when a huge asteroid struck the young Earth 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 Venus is covered with gently rolling hills, two "continents," and numerous volcanoes 177 MARS Mars's global features include plains, canyons, craters, and volcanoes While no canals exist on Mars, it does have small bizarre features Mars's interior is less molten than the inside of the Earth Martian air is thin and often filled with dust Surface features indicate that water once flowed on Mars 188

5 7-13 Search for microscopic life on Mars continues Mars has a crust of varying thickness Mars's two moons look more like potatoes than spheres Comparisons of planetary features provides new insights Frontiers yet to be discovered 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 SATURN Saturn's surface and interior are similar to those of Jupiter Saturn's spectacular rings are composed of fragments of ice and ice-coated rock Titan has a thick, opaque atmosphere rich in nitrogen, methane, and other hydrocarbons 220 URANUS Uranus sports a hazy atmosphere and clouds A system of rings and satellites revolves around Uranus 225 NEPTUNE Neptune was discovered because it had to be there Neptune has rings and has captured most of its moons 228 PLUTO AND BEYOND Pluto and its moon, Charon, are about the same size Comparative planetology of the outer planets Frontiers yet to be discovered What If... We Lived on a Metal-poor Earth? 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 MET 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 Asteroid impacts with Earth have caused mass extinctions Frontiers yet to be discovered r The Sun: Our Extraordinary IP Ordinary Star 267 THE SUN'S ATMOSPHERE The photosphere is the visible layer of the Sun The chromosphere is characterized by spikes of gas called spicules Temperatures increase higher in the Sun's atmosphere 271

6 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 THE SUN'S INTERIOR Thermonuclear reactions in the core of the Sun produce its energy 281 AN ASTRONOMER'S TOOLBOX 10-1 Thermonuclear Fusion Solar models describe how energy escapes ' from the Sun's core The mystery of the missing neutrinos inspired research into the fundamental nature of matter Frontiers yet to be discovered ~ P a r t 111 llllmstanding THE STARS Qi Characterizing Stars 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 Apparent magnitude measures the brightness of stars as seen from Earth 296 AN ASTRONOMER'S TOOLBOX 11-2 Details of the Magnitude Scales 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 A star's color reveals its surface temperature A star's spectrum also reveals its surface temperature 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 STELLAR MASSES Binary stars provide information about stellar masses 307 AN ASTRONOMER'S TOOLBOX 11-4 Kepler's Third Law and Stellar Masses There is a relationship between mass and luminosity for main-sequence stars The orbital motion of binary stars affects the wavelengths of their spectral lines Some binary stars eclipse each other Frontiers yet to be discovered [12 The Lives of Stars from Birth Through Middle Age 317 PROTOSTARS AND PRE-MAIN-SEQUENCE STARS Gas and dust exist between the stars Supernovae, collisions of interstellar clouds, and starlight trigger new star formation 322 GUIDED DISCOVERY Observing the Nebulae When a protostar ceases to accumulate mass, it becomes a pre-main-sequence star The evolutionary track of a pre-main-sequence star depends on its mass 326 GUIDED DISCOVERY Extrasolar Planets and Brown Dwarfs H II regions harbor young star clusters Plotting a star cluster on an H-R diagram reveals its age 331 MAIN-SEQUENCE AND GIANT STARS Stars spend most of their life cycles on the main sequence 332 EVOLUTION OF STARS WITH MASSES BETWEEN O.O8 AND O.4 M Red dwarfs convert essentially their entire mass into helium 333

7 EARLY AND MIDLIFE EVOLUTION OF STARS WITH MORE THAN 0.4 M Q When core hydrogen fusion slows down, a main-sequence star with M > 0.4 M 0 becomes a giant Helium fusion begins at the center of a giant As stars evolve, their positions on the H-R diagram shift Globular clusters are bound groups of old stars 338 VARIABLE STARS A Cepheid pulsates because it is alternately expanding and contracting Cepheids enable astronomers to estimate vast distances Mass transfer in close binary systems can produce unusual double stars Frontiers yet to be discovered What If... The Earth Orbited a 1.5 M n Sun? 348 [13 The Deaths of Stars 349 LOW-MASS STARS AND PLANETARY NEBULAE Lower-mass stars become supergiants before expanding into planetary nebulae The burned-out core of a low-mass star becomes a white dwarf White dwarfs in close binary systems can create powerful explosions 354 INTERMEDIATE-MASS STARS, HIGH-MASS STARS, AND SUPERNOVAE A series of fusion reactions in intermediate-mass and high-mass stars leads to luminous supergiants Both intermediate-mass and high-mass stars blow apart in violent supernova explosions Supernovae occur in our Galaxy, among many others Cosmic rays are not rays at all Supernova 1987A offered a detailed look at a massive star's death Accreting white dwarfs in close binary systems can also explode as supernovae 363 NEUTRON STARS AND PULSARS The cores of many Type II supernovae become neutron stars A rotating magnetic field explains the pulses from a neutron star Colliding neutron stars may provide some of the heavy elements in the universe Binary neutron stars create pulsating X-ray sources Neutron stars in binary systems can also emit powerful isolated bursts of X rays There may exist smaller, more exotic stellar remnants composed of quarks Frontiers yet to be discovered What If... A Supernova Exploded Near Earth? 375 [ 4 Black Holes: Matters of Gravity 376 THE RELATIVITY THEORIES Special relativity changes our conception of space and time General relativity explains how matter warps spacetime, creating gravitational attraction Spacetime affects the behavior of light General relativity predicts the fate of massive star cores black holes 381 INSIDE A BLACK HOLE 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 Falling into a black hole is an infinite voyage Several binary star systems contain black holes 385 GUIDED DISCOVERY Identifying Stellar-Remnant Black Holes Other black holes range in mass up to billions of solar masses Black holes and neutron stars in binary systems often create jets of gas 389

8 GAMMA-RAY BURSTS Gamma-ray bursts are the most powerful explosions in the known universe Black holes evaporate 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 CLUSTERS AND SUPERCLUSTERS Galaxies occur in clumps called clusters, which occur in clumps called superclusters Clusters of galaxies may appear densely or sparsely populated and regular or irregular in shape Galaxies in a cluster can collide and combine Galatic halos may account for some dark matter in the universe 433 SUPERCLUSTERS IN MOTION 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 Different techniques determine the expansion of the universe at different distances from Earth Astonomers are looking back to a time -. when galaxies were first forming Frontiers yet to be discovered 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 ACTIVE GALAXIES Active galaxies bridge the energy gap between ordinary galaxies and quasars BL Lacertae objects and blazars are brighter than either quasars or active galaxies Active galaxies emit twin jets of gas that span galaxies 452 SUPERMASSIVE ENGINES Supermassive black holes exist at the centers of most galaxies Jets of matter ejected from around

9 black holes explain BL Lac objects, quasars, active galaxies, and double radio sources Gravity focuses light from quasars Frontiers yet to be discovered 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 A BRIEF HISTORY OF SPACETIME, MATTER, ENERGY, AND EVERYTHING All physical forces in nature were unified at first Equations explain the evolution of the universe even before matter and energy as we know it existed During the first second, most of the matter and antimatter in the universe annihilated each other The universe changed from being controlled by radiation to being controlled by matter Inflation explains why the universe is isotropic and homogeneous Galaxies formed from huge clouds of primordial gas Star formation activity determines a galaxy's initial structure 477 THE FATE OF THE UNIVERSE The average density of matter is one factor that determines the future of the universe The overall shape of spacetime affects the future of the universe Dark energy is causing the universe to accelerate outward Frontiers yet to be discovered The Search for Extraterrestrial Life The existence of life depends on chemical and physical properties of matter Evidence is mounting that life might exist elsewhere in our solar system Searches under way for advanced civilizations try to detect their radio signals The Drake equation: How many civilizations are likely to exist in the Milky Way? Humans have been sending signals into space for more than a century Frontiers yet to be discovered 494 What If... Life Had Begun on an Older Earth? 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