Discovering the Universe

Cover
Title Page
Copyright Page
Contents Overview
Contents
Preface
About the Author
PART I: Understanding the Science of Astronomy
	CHAPTER 1: Discovering the Night Sky
		SCALES OF THE UNIVERSE
			1-1 Astronomical distances are, well, astronomical
		PATTERNS OF STARS
			1-2 Well-known constellations make locating more obscure stars and constellations easy
			1-3 The celestial sphere aids in navigating the sky
		GUIDED DISCOVERY The Stars and Constellations
			1-4 An “alt”ernative coordinate system
			1-5 Earth orbits the Sun in a plane called the ecliptic
		EARTHLY CYCLES
			1-6 Earth’s rotation creates the day-night cycle and its revolution defines a year
		AN ASTRONOMER’S TOOLBOX 1-1 Observational Measurements Using Angles
			1-7 The seasons result from the tilt of Earth’s rotation axis combined with Earth’s revolution around the Sun
			1-8 Clock times based on the Sun’s location created scheduling nightmares
			1-9 Calendars based on equal-length years also created scheduling problems
			1-10 Precession is a slow, circular motion of Earth’s axis of rotation
			1-11 The phases of the Moon originally inspired the concept of the month
		ECLIPSES
			1-12 Eclipses do not occur during every new or full Moon phase
			1-13 Three types of lunar eclipse occur
			1-14 Three types of solar eclipse also occur
			1-15 Frontiers yet to be discovered
		Summary of Key Ideas
		WHAT IF... Earth’s Axis Lay on the Ecliptic?
	CHAPTER 2: Gravitation and the Motion of the Planets
		SCIENCE: KEY TO COMPREHENDING THE COSMOS
			2-1 Science is both a body of knowledge and a process of learning about nature
		CHANGING OUR EARTH-CENTERED VIEW OF THE UNIVERSE
			2-2 The belief in a Sun-centered cosmology formed slowly
		GUIDED DISCOVERY Earth-Centered Universe
			2-3 Copernicus devised the first comprehensive heliocentric cosmology
		GUIDED DISCOVERY Astronomy’s Foundation Builders
			2-4 Tycho Brahe made astronomical observations that disproved ancient ideas about the heavens
		KEPLER’S AND NEWTON’S LAWS
			2-5 Kepler’s laws describe orbital shapes, changing speeds, and the lengths of planetary years
			2-6 Galileo’s discoveries strongly supported a heliocentric cosmology
		AN ASTRONOMER’S TOOLBOX 2-1 Units of Astronomical Distance
			2-7 Newton formulated three laws that describe fundamental properties of physical reality
		AN ASTRONOMER’S TOOLBOX 2-2 Energy and Momentum
			2-8 Newton’s description of gravity accounts for Kepler’s laws
		AN ASTRONOMER’S TOOLBOX 2-3 Gravitational Force
			2-9 Orbiting bodies orbit a common center of mass
			2-10 Ellipses are not the only paths followed by gravitationally interacting objects
			2-11 Frontiers yet to be discovered
		Summary Of Key Ideas
	CHAPTER 3: Light and Telescopes
		ELECTROMAGNETIC RADIATION OBSERVATORIES
			3-1 Newton discovered that white is not a fundamental color and proposed that light is composed of particles
			3-2 Light travels at a finite but incredibly fast speed
			3-3 Einstein showed that light sometimes behaves as particles that carry energy
		AN ASTRONOMER’S TOOLBOX 3-1 Photon Energies, Wavelengths, and Frequencies
			3-4 Visible light is only one type of electromagnetic radiation
		OPTICS AND TELESCOPES
			3-5 Reflecting telescopes use mirrors to concentrate incoming starlight
			3-6 Secondary mirrors dim objects but do not create holes in them
			3-7 Telescopes brighten, resolve, and magnify
			3-8 Eyepieces, refracting telescopes, and binoculars use lenses to focus incoming light
			3-9 Shaping telescope mirrors and lenses is an evolving science
			3-10 Storing and analyzing light from space is key to understanding the cosmos
			3-11 Earth’s atmosphere hinders astronomical research
			3-12 The Hubble Space Telescope provides stunning details about the universe
			3-13 Advanced technology is spawning a new generation of superb ground-based telescopes
		NONOPTICAL ASTRONOMY
			3-14 A radio telescope uses a large concave dish to collect radio waves
			3-15 Infrared and ultraviolet telescopes also use reflectors to collect electromagnetic radiation
			3-16 X-ray and gamma-ray telescopes cannot use normal reflectors to gather information
		COSMIC RAY OBSERVATORIES
			3-17 Cosmic rays are not rays at all
		NEUTRINO OBSERVATORIES
			3-18 The mystery of the missing neutrinos inspired development of telescopes to detect these elusive particles
		GRAVITATIONAL WAVE OBSERVATORIES
			3-19 Gravitational radiation observatories provide insights into very violent activities, such as the collisions of stellar remnants
			3-20 Frontiers yet to be discovered
		Summary of Key Ideas
		WHAT IF... Humans Had Infrared-Sensitive Eyes?
	CHAPTER 4: Atomic Physics and Spectra
		BLACKBODY RADIATION
			4-1 An object’s peak color shifts to shorter wavelengths as it is heated
			4-2 The intensities of different emitted colors reveal a star’s temperature
		AN ASTRONOMER’S TOOLBOX 4-1 The Radiation Laws
		GUIDED DISCOVERY The Color of the Sun
		IDENTIFYING THE ELEMENTS BY ANALYZING THEIR UNIQUE SPECTRA
			4-3 Each chemical element produces its own unique set of spectral lines
			4-4 The various brightness levels of spectral lines depend on conditions in the spectrum’s source
		ATOMS AND SPECTRA
			4-5 An atom consists of a small, dense nucleus surrounded by electrons
		AN ASTRONOMER’S TOOLBOX 4-2 Radioactivity and the Ages of Objects
			4-6 Spectra occur because electrons absorb and emit photons with only certain wavelengths
			4-7 Spectral lines shift due to the relative motion between the source and the observer
		AN ASTRONOMER’S TOOLBOX 4-3 The Doppler Shift
			4-8 Frontiers yet to be discovered
		Summary of Key Ideas
PART II: Understanding the Solar System and Exoplanets
	CHAPTER 5: Exoplanets and the Formation of Planetary Systems
		EXOPLANETS—PLANETS OUTSIDE OUR SOLAR SYSTEM
		PLANETS CONTAIN HEAVY ELEMENTS, FORMED IN EARLIER GENERATIONS OF STARS
			5-1 Stars transform matter from lighter elements into heavier ones
			5-2 Gravity, rotation, collisions, and heat shape young star systems
			5-3 Protoplanetary disks are a common part of the star-forming process
			5-4 Astronomers have many different ways of detecting planets outside our solar system
		METHODS OF DETECTING EXOPLANETS
			5-5 Exoplanets orbit a breathtaking variety of stars
			5-6 Exoplanets with a wide range of sizes, masses, and compositions have been observed
			5-7 Stars with multiple exoplanets have been observed
			5-8 Many exoplanets have extraordinary orbits, as compared to those in our solar system
			5-9 Exoplanets that are not orbiting stars have also been observed
			5-10 There are billions and billions of exoplanets
			5-11 Exoplanets with liquid water are being discovered
			5-12 Frontiers yet to be explored
		Summary of Key Ideas
		MEET THE DISCOVERERS Dr. John Johnson
	CHAPTER 6: Formation of the Solar System
		THE SOLAR SYSTEM CONTAINS HEAVY ELEMENTS, FORMED FROM AN EARLIER GENERATION OF STARS
			6-1 The Nice model of the formation of the solar system
		THE FORMATION OF THE PLANETS
			6-2 The giant planets formed in sequence
			6-3 The inner planets formed primarily from collisions
			6-4 The changing orbits of the giant planets caused Uranus and Neptune to spiral out
			6-5 The solar system had, and still has, a lot of orbiting debris
			6-6 The asteroid belt is also leftover debris
			6-7 The infalling debris from the giant planets led to the Late Heavy Bombardment
		CATEGORIES OF THE PRESENT-DAY SOLAR SYSTEM
			6-8 The categories of solar system objects have evolved
			6-9 The orbits of the planets are related
			6-10 The Sun developed while the planets matured
		COMPARATIVE PLANETOLOGY
			6-11 Comparisons among the eight planets show distinct similarities and significant differences
			6-12 How does the solar system compare to star systems with known exoplanets?
			6-13 Frontiers yet to be discovered
		Summary of Key Ideas
	CHAPTER 7: Earth and the Moon
		EARTH: A DYNAMIC, VITAL WORLD
			7-1 Earth’s atmosphere has evolved over billions of years
			7-2 Plate tectonics produce major changes on Earth’s surface
			7-3 Earth’s interior consists of a rocky mantle and an iron-rich core
			7-4 Earth’s magnetic field shields us from the solar wind
		THE MOON AND TIDES
			7-5 The Moon’s surface is covered with craters, plains, and mountains
			7-6 Visits to the Moon yielded invaluable information about its history
			7-7 The Moon may have formed from debris cast into space when a huge planetesimal struck the young Earth
			7-8 Tides have played several important roles in the history of Earth and the Moon
			7-9 The Moon is moving away from Earth
		GUIDED DISCOVERY Tides
			7-10 Frontiers yet to be discovered
		SUMMARY OF KEY IDEAS
		WHAT IF... The Moon Didn’t Exist?
	CHAPTER 8: The Other Terrestrial Planets
		MERCURY
			8-1 Photographs from Mariner 10 and MESSENGER spacecraft reveal Mercury’s lunarlike surface
			8-2 Mercury has a higher percentage of iron than Earth
			8-3 Mercury’s rotation and revolution are coupled
			8-4 Mercury’s atmosphere is the thinnest of all terrestrial planets
		VENUS
			8-5 The surface of Venus is completely hidden beneath a permanent cloud cover
		GUIDED DISCOVERY The Inner Solar System
			8-6 The greenhouse effect heats Venus’s surface
			8-7 Venus is covered with gently rolling hills, two “continents,” and numerous volcanoes
		MARS
			8-8 Mars’s global features include plains, canyons, craters, and volcanoes
			8-9 Although no canals exist on Mars, it does have some curious natural features
			8-10 Mars’s interior is less molten than the inside of Earth
			8-11 Martian air is thin and often filled with dust
			8-12 Surface and underground features indicate that water once flowed and may still flow in small quantities on Mars
			8-13 Search for microscopic life on Mars continues
			8-14 Mars’s two moons look more like potatoes than spheres
		COMPARATIVE PLANETOLOGY OF THE INNER PLANETS
			8-15 Comparisons of planetary features provide new insights
			8-16 Frontiers yet to be discovered
		Summary of Key Ideas
		MEET THE DISCOVERERS Dr. Briony Horgan
	CHAPTER 9: The Outer Planets
		JUPITER
			9-1 Jupiter’s outer layer is a dynamic area of storms and turbulent gases
			9-2 Our understanding of Jupiter’s interior is in flux
			9-3 Impacts provide probes into Jupiter’s atmosphere
		JUPITER’S MOONS AND RINGS
			9-4 Io’s surface is sculpted by volcanic activity
			9-5 Europa harbors liquid water below its surface
			9-6 Ganymede is larger than Mercury
			9-7 Callisto bears the scars of a huge asteroid impact
			9-8 Other debris orbits Jupiter as smaller moons and ringlets
		SATURN
			9-9 Saturn’s atmosphere, surface, and interior are similar to those of Jupiter
			9-10 Saturn’s spectacular rings are composed of fragments of ice and ice-coated rock
			9-11 Titan has a thick atmosphere, clouds, and lakes filled with liquids
			9-12 Rhea has ice
			9-13 Enceladus has water jets, an atmosphere, and a magnetic field
		URANUS
			9-14 Uranus sports a hazy atmosphere and clouds
			9-15 A system of rings and satellites revolves around Uranus
		NEPTUNE
			9-16 Neptune was discovered because it had to be there
			9-17 Neptune has rings and captured moons
		COMPARATIVE PLANETOLOGY OF THE OUTER PLANETS
			9-18 Frontiers yet to be discovered
		Summary Of Key Ideas
		WHAT IF... We Lived on a Metal-Poor Earth?
	CHAPTER 10: Vagabonds of the Solar System
		DWARF PLANETS
			10-1 Pluto and its moon, Charon, are about the same size
			10-2 Ceres is a dwarf planet in the asteroid belt, while Pluto, Eris, Haumea, and Makemake are trans-Neptunian objects as well as dwarf planets
		SMALL SOLAR SYSTEM BODIES
		ASTEROIDS
			10-3 Most asteroids orbit the Sun between Mars and Jupiter
			10-4 Jupiter’s gravity creates gaps in the asteroid belt
			10-5 Asteroids also orbit outside the asteroid belt
		COMETS
			10-6 Comets come from far out in the solar system
			10-7 Comet tails develop from gases and dust pushed outward by the Sun
			10-8 Comets are fragile yet durable
			10-9 Comets do not last forever
		METEOROIDS, METEORS, AND METEORITES
			10-10 Small, rocky debris peppers the solar system
			10-11 Meteorites are space debris that land intact
			10-12 The Allende meteorite provides evidence of catastrophic explosions
			10-13 Asteroid impacts with Earth have caused mass extinctions
			10-14 Frontiers yet to be discovered
		Summary of Key Ideas
		MEET THE DISCOVERERS Dr. Cristina Thomas
	CHAPTER 11: The Sun: Our Extraordinary Ordinary Star
		THE SUN’S ATMOSPHERE
			11-1 The photosphere is the visible layer of the Sun
			11-2 The chromosphere is characterized by spikes of gas called spicules
			11-3 The outermost layer of the Sun’s atmosphere, the corona, is exceptionally hot
			11-4 The solar wind produces the heliosphere that surrounds the solar system
		THE ACTIVE SUN
			11-5 Sunspots reveal the solar cycle and the Sun’s rotation
			11-6 The Sun’s magnetic fields create sunspots
			11-7 Solar magnetic fields also create other atmospheric phenomena
		THE SUN’S INTERIOR
			11-8 Thermonuclear reactions in the core of the Sun produce its energy
			11-9 The solar model describes how energy escapes from the Sun’s core
			11-10 The Sun has gotten brighter over time
		AN ASTRONOMER’S TOOLBOX 11-1 Thermonuclear Fusion
			11-11 Neutrinos from the Sun and other sources are providing new insights into high-energy activity in space
			11-12 Frontiers yet to be discovered
		Summary of Key Ideas
PART III: Understanding the Stars
	CHAPTER 12: Characterizing Stars
		12-1 Distances to nearby stars are found using stellar parallax
		AN ASTRONOMER’S TOOLBOX 12-1 Distances to Nearby Stars
		AN ASTRONOMER’S TOOLBOX 12-2 Details of the Magnitude Scales
		MAGNITUDE SCALES
			12-2 Apparent magnitude measures the brightness of stars as seen from Earth
			12-3 Absolute magnitudes and luminosities do not depend on distance
		GUIDED DISCOVERY Star Names
		AN ASTRONOMER’S TOOLBOX 12-3 The Distance- Magnitude Relationship
		THE TEMPERATURES OF STARS
			12-4 A star’s color reveals its surface temperature
			12-5 A star’s spectrum also reveals its surface temperature
			12-6 Stars are classified by their spectra
		TYPES OF STARS
			12-7 The Hertzsprung-Russell diagram identifies distinct groups of stars
			12-8 Luminosity classes set the stage for understanding stellar evolution
			12-9 A star’s spectral type and luminosity class provide a second distance-measuring technique
		STELLAR MASSES
			12-10 Binary stars provide information about stellar masses
		AN ASTRONOMER’S TOOLBOX 12-4 Kepler’s Third Law and Stellar Masses
			12-11 Main-sequence stars have a relationship between mass and luminosity
			12-12 The orbital motion of binary stars affects the wavelengths of their spectral lines
			12-13 Frontiers yet to be discovered
		Summary of Key Ideas
	CHAPTER 13: The Lives of Stars from Birth Through Middle Age
		PROTOSTARS AND PRE–MAIN-SEQUENCE STARS
			13-1 Gas and dust exist between the stars
			13-2 Supernovae, collisions of interstellar clouds, and starlight trigger new star formation
		GUIDED DISCOVERY Observing the Nebulae
			13-3 When a protostar ceases to accumulate mass, it becomes a pre–main-sequence star
			13-4 The evolutionary track of a pre–main-sequence star depends on its mass
		GUIDED DISCOVERY Extrasolar Planets and Brown Dwarfs
			13-5 H II regions harbor young star clusters
			13-6 Plotting a star cluster on an H-R diagram reveals its age
		MAIN-SEQUENCE AND GIANT STARS
			13-7 Stars spend most of their lives on the main sequence
		EVOLUTION OF STARS WITH MASSES BETWEEN 0.08 M⊙ AND 0.4 M⊙
			13-8 Red dwarfs convert essentially their entire mass into helium
		EARLY AND MIDDLE EVOLUTION OF STARS WITH MORE THAN 0.4 M⊙
			13-9 When core hydrogen fusion slows down, a main-sequence star with mass greater than 0.4 M⊙ becomes a giant
			13-10 Helium fusion begins at the center of a giant
			13-11 Life in the giant phase has its ups and downs
		VARIABLE STARS
			13-12 A Cepheid pulsates because it is alternately expanding and contracting
			13-13 Cepheids enable astronomers to estimate vast distances
			13-14 Globular clusters are bound groups of old stars
			13-15 Mass transfer in close binary systems can produce unusual double stars
			13-16 Frontiers yet to be discovered
		Summary of Key Ideas
		WHAT IF... Earth Orbited a 1.5-M⊙ Sun?
	CHAPTER 14: The Deaths of Stars
		LOW-MASS (0.4 M⊙–8 M⊙) STARS AND PLANETARY NEBULAE
			14-1 Low-mass stars become supergiants before expanding into planetary nebulae
			14-2 The burned-out core of a low-mass star becomes a white dwarf
			14-3 White dwarfs in close binary systems can create powerful explosions
			14-4 Accreting white dwarfs in close binary systems can also explode as Type Ia supernovae
		HIGH-MASS (GREATER THAN 8 M⊙) STARS AND TYPE II SUPERNOVAE
			14-5 A series of fusion reactions in high-mass stars leads to luminous supergiants
			14-6 High-mass stars blow apart in Type II supernova explosions
			14-7 Supernova remnants are observed in many places
			14-8 Supernova 1987A offered a detailed look at a massive star’s death
			14-9 Cosmic rays are not rays at all
		NEUTRON STARS AND PULSARS
			14-10 The cores of many Type II supernovae become neutron stars
			14-11 A rotating magnetic field explains the pulses from a neutron star
			14-12 Rotating neutron stars create other phenomena besides normal pulsars
			14-13 Neutron stars have internal structure
			14-14 Some pulsars are in binary systems
			14-15 Superluminous supernovae are much brighter than either Type Ia or Type II supernovae
			14-16 Supernova impostors
			14-17 Fast radio bursts
			14-18 Colliding neutron stars provide most of the heavy elements in the universe
			14-19 Binary neutron stars create pulsating X-ray sources
			14-20 Neutron stars in binary systems can also emit powerful isolated bursts of X-rays
			14-21 Frontiers yet to be discovered
		Summary of Key Ideas
		WHAT IF... A Supernova Exploded Near Earth?
		MEET THE DISCOVERERS Dr. Anna Frebel
	CHAPTER 15: Black Holes: Matters of Gravity
		THE RELATIVITY THEORIES
			15-1 Special relativity changes our conception of space and time
			15-2 General relativity explains how matter warps spacetime, thereby creating gravitational attraction
			15-3 Spacetime affects the behavior of light
			15-4 General relativity predicts the fate of massive stellar cores—black holes
		AN ASTRONOMER’S TOOLBOX 15-1 The Sizes of Black Holes
		INSIDE A BLACK HOLE
			15-5 Matter in a black hole becomes much simpler than elsewhere in the universe
			15-6 Falling into a black hole is an infinite voyage
		GRAVITATIONAL RADIATION
		FURTHER EVIDENCE FOR BLACK HOLES
			15-7 Several binary star systems contain black holes
			15-8 Other black holes range in mass up to billions of solar masses
		GUIDED DISCOVERY Identifying Stellar-Remnant Black Holes
			15-9 Black holes and neutron stars in binary systems often create jets of gas
			15-10 Black holes evaporate
		GAMMA-RAY BURSTS
			15-11 Gamma-ray bursts are the most powerful explosions in the known universe
			15-12 Frontiers yet to be discovered
		Summary of Key Ideas
		MEET THE DISCOVERER Dr. Scott A. Hughes
PART IV: Understanding the Universe
	CHAPTER 16: The Milky Way Galaxy
		DEFINING THE MILKY WAY
			16-1 Studies of Cepheid variable stars revealed that the Milky Way is only one of many galaxies
		AN ASTRONOMER’S TOOLBOX 16-1 Cepheids and Type Ia Supernovae as Indicators of Distance
		THE STRUCTURE OF OUR GALAXY AND OUR PLACE IN IT
			16-2 Cepheid variables help us locate our Galaxy’s center
			16-3 Nonvisible observations help map the galactic disk
			16-4 The Milky Way has a global magnetic field
			16-5 The galactic nucleus is an active, crowded place
			16-6 Our Galaxy’s disk is surrounded by a two-shell spherical halo of stars and other matter
			16-7 The Galaxy is rotating
		MYSTERIES AT THE GALACTIC FRINGES
			16-8 Most of the matter in the Galaxy has not yet been identified
			16-9 Frontiers yet to be discovered
		Summary of Key Ideas
	CHAPTER 17: Galaxies
		TYPES OF GALAXIES
			17-1 For many spiral galaxies, the winding of their spiral arms is correlated to the size of a central bulge
			17-2 Explosions create flocculent spirals, and waves create grand-design spirals
			17-3 Bars of stars run through the central bulges of barred spiral galaxies, and some disk galaxies, the lenticulars, lack spiral arms
			17-4 Elliptical galaxies display a wide variety of sizes and masses
			17-5 Galaxies without global structure are called irregular
			17-6 Hubble presented spiral and elliptical galaxies in a tuning fork-shaped diagram
			17-7 Galaxies built up in size over time
		CLUSTERS AND SUPERCLUSTERS
			17-8 Galaxies exist in clusters, which are clustered in larger clumps called superclusters
			17-9 Clusters of galaxies may appear densely or sparsely populated and regular or irregular in shape
			17-10 Galaxies in a cluster can collide and combine
			17-11 Dark matter helps hold together individual galaxies and clusters of galaxies
		SUPERCLUSTERS IN MOTION
			17-12 The redshifts of superclusters indicate that the universe is indeed expanding
		GUIDED DISCOVERY The Tully–Fisher Relation and Other Distance-Measuring Techniques
			17-13 Astronomers are looking back to a time when galaxies were first forming
		AN ASTRONOMER’S TOOLBOX 17-1 The Hubble–Lemaître Law
		GUIDED DISCOVERY The Expanding Universe
			17-14 Frontiers yet to be discovered
		SUMMARY OF KEY iDEAS
		WHAT iF... The Solar System Were Located Closer to the Center of the Galaxy?
		MEET THE DISCOVERERS Dr. Kartik Sheth
	CHAPTER 18: Quasars and Other Active Galaxies
		QUASARS
			18-1 Quasars look like stars but have huge redshifts
			18-2 A quasar emits a huge amount of energy from a small volume
		OTHER ACTiVE GALAxiES
			18-3 Active galaxies can be either spiral or elliptical
		SUPERMASSiVE ENGiNES
			18-4 Supermassive black holes exist at the centers of most galaxies
			18-5 Jets of protons and electrons ejected from around black holes explain quasars, Seyfert galaxies, radio galaxies, double-radio sources, and BL Lacertae objects
			18-6 Gravity focuses light from quasars
			18-7 Fast radio bursts
			18-8 Frontiers yet to be discovered
		Summary of Key ideas
	CHAPTER 19: Cosmology
		THE BIG BANG
			19-1 General relativity predicts an expanding (or contracting) universe
			19-2 The expansion of the universe creates a Dopplerlike redshift
			19-3 The Hubble constant is related to the age of the universe
		AN ASTRONOMER’S TOOLBOX 19-1 Ho and the Age of the Universe
			19-4 Remnants of the Big Bang have been detected
			19-5 The universe has two symmetries—isotropy and homogeneity
		A BRiEF HiSTORY OF SPACETiME, MATTER, ENERGY, AND EVERYTHiNG
			19-6 All physical forces in nature were initially unified
			19-7 Equations explain the evolution of the universe, even before matter and energy, as we know them, existed
			19-8 Homogeneity and isotropy are results of inflation
			19-9 During the first second, most of the matter and antimatter in the universe annihilated each other
			19-10 The universe changed from being controlled by radiation to being controlled by matter
			19-11 Galaxies formed from huge clouds of primordial gas
			19-12 Star formation activity determines a galaxy’s initial structure
		THE FATE OF THE UNiVERSE
			19-13 The average density of matter is one factor that determines the future of the universe
			19-14 The overall shape of spacetime affects the future of the universe
			19-15 Dark energy is causing the universe to accelerate outward
		GUIDED DISCOVERY Superstring Theory and M-Theory
			19-16 Frontiers yet to be discovered
		Summary of Key ideas
		MEET THE DISCOVERERS Dr. Yun Wang
	CHAPTER 20: Astrobiology
		20-1 Astrobiology connects the cosmos and the origins of life
		20-2 The existence of life depends on chemical and physical properties of matter
		20-3 Evidence is mounting that life might exist elsewhere in our solar system
		20-4 Searches for advanced civilizations try to detect their radio signals
		20-5 The Drake equation: How many civilizations are likely to exist in the Milky Way?
		20-6 Humans have been sending signals into space for more than a century
		20-7 Frontiers yet to be discovered
		Summary of Key Ideas
		MEET THE DISCOVERERS Dr. Magdelena Osburn
APPENDICES
	APPENDIX A: Powers-of-Ten Notation
	APPENDIX B: Guidelines for Solving Math Problems and Reading Graphs
	APPENDIX C: Key Formulas
	APPENDIX D: Temperature Scales
	APPENDIX E: Data Tables
	APPENDIX F: Periodic Table of the Elements
	APPENDIX G: Largest Optical Telescopes in the World
	APPENDIX H: Buying a Telescope
Glossary
Answers to Selected Questions
Index