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510 Cards in this Set

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  • Back
Chapter 1
astronomical unit (AU)
Average distance from Earth to the sun; 1.5 x 108 km, or 93 x 106 mi. (p. 6)
A large system of stars, star clusters, gas, dust, and nebulae orbiting a common center of mass. (p. 8)
light-year (ly)
A unit of distance. The distance light travels in 1 year. (p. 7)
Milky Way
The hazy band of light that circles our sky. Produced by the glow of our galaxy. (p. 8)
Milky Way Galaxy
The spiral galaxy containing our sun. Visible in the night sky as the Milky Way. (p. 8)
A small, nonluminous body formed by accretion in a disk around a protostar. (p. 6)
scientific notation
The system of recording very large or very small numbers by using powers of 10. (p. 6)
solar system
The sun and its planets, asteroids, comets, and so on. (p. 6)
spiral arm
Long spiral pattern of bright stars, star clusters, gas, and dust. Spiral arms extend from the center to the edge of the disk of spiral galaxies. (p. 8)
A globe of gas held together by its own gravity and supported by the internal pressure of its hot gases, which generate energy by nuclear fusion. (p. 6)
Chapter 2
angular diameter
The angle formed by lines extending from the observer to opposite sides of an object. (p. 21)
angular distance
The angle formed by lines extending from the observer to two locations. (p. 21)
apparent visual magnitude (mv)
The brightness of a star as seen by human eyes on Earth. (p. 16)
A named grouping of stars that is not one of the recognized constellations. Examples are the Big Dipper and the Pleiades. (p. 15)
celestial equator
The imaginary line around the sky directly above Earth's equator. (p. 20)
celestial pole (north or south)
One of the two points on the celestial sphere directly above Earth's poles. (p. 20)
celestial sphere
An imaginary sphere of very large radius surrounding Earth and to which the planets, stars, sun, and moon seem to be attached. (p. 20)
circumpolar constellation (north or south)
A constellation so close to one of the celestial poles that it never sets or never rises as seen from a particular latitude. (p. 21)
One of the stellar patterns identified by name, usually of mythological gods, people, animals, or objects. Also, the region of the sky containing that star pattern. (p. 14)
east point
One of the four cardinal directions. The point on the horizon directly east. (p. 20)
The circular boundary between the sky and Earth. (p. 20)
magnitude scale
The astronomical brightness scale. The larger the number, the fainter the star. (p. 15)
minute of arc
An angular measure. One sixtieth of a degree. (p. 21)
See scientific model.
The point on the celestial sphere directly below the observer. The opposite of the zenith. (p. 20)
north celestial pole
The point on the celestial sphere directly above Earth's North Pole. (p. 20)
north point
One of the four cardinal directions. The point on the horizon directly north. (p. 20)
The slow change in the direction of Earth's axis of rotation. One cycle takes nearly 26,000 years. (p. 18)
scientific model
A tentative description of a phenomenon for use as an aid to understanding. (p. 18)
second of arc
An angular measure. One sixtieth of a minute of arc. (p. 21)
south celestial pole
The point on the celestial sphere directly above Earth's South Pole. (p. 20)
south point
One of the four cardinal directions. The point on the horizon directly south. (p. 20)
west point
One of the four cardinal directions. The point on the horizon directly west. (p. 20)
The point on the sky directly above the observer. (p. 20)
Chapter 3
annular eclipse
A solar eclipse in which the solar photosphere appears around the edge of the moon in a bright ring, or annulus. The corona, chromosphere, and prominences cannot be seen. (p. 37)
The orbital point of greatest distance from the sun. (p. 29)
The point farthest from Earth in the orbit of a body circling Earth. (p. 37)
autumnal equinox
The point on the celestial sphere where the sun crosses the celestial equator going southward. Also, the time when the sun reaches this point and autumn begins in the northern hemisphere - about September 22. (p. 28)
Bright gases just above the photosphere of the sun. (p. 36)
On the sun, the faint outer atmosphere composed of low-density, high-temperature gas. (p. 37)
diamond-ring effect
During a total solar eclipse, the momentary appearance of a spot of photosphere at the edge of the moon, producing a brilliant glare set in the silvery ring of the corona. (p. 37)
The apparent path of the sun around the sky. (p. 26)
evening star
Any planet visible in the sky just after sunset. (p. 30)
lunar eclipse
The darkening of the moon when it moves through Earth's shadow. (p. 31)
Milankovitch hypothesis
Suggestion that Earth's climate is determined by slow periodic changes in the shape of its orbit, the angle of its axis, and precession. (p. 40)
morning star
Any planet visible in the sky just before sunrise. (p. 30)
The points where an object's orbit passes through the plane of Earth's orbit. (p. 39)
The portion of a shadow that is only partially shaded. (p. 31)
The point closest to Earth in the orbit of a body circling Earth. (p. 37)
The orbital point of closest approach to the sun. (p. 29)
The bright visible surface of the sun. (p. 36)
Eruption on the solar surface. Visible during total solar eclipses. (p. 37)
Orbital motion about a point located outside the orbiting body. See also rotation. (p. 24)
Motion around an axis passing through the rotating body. See also revolution. (p. 24)
Saros cycle
An 18-year, 11-1/3-day period after which the pattern of lunar and solar eclipses repeats. (p. 39)
sidereal period
The time a celestial body takes to turn once on its axis or revolve once around its orbit relative to the stars. (p. 33)
solar eclipse
The event that occurs when the moon passes directly between Earth and the sun, blocking our view of the sun. (p. 35)
summer solstice
The point on the celestial sphere where the sun is at its most northerly point. Also, the time when the sun passes this point, about June 22, and summer begins in the northern hemisphere. (p. 28)
synodic period
The time a solar system body takes to orbit the sun once and return to the same orbital relationship with Earth. That is, orbital period referenced to Earth. (p. 33)
The region of a shadow that is totally shaded. (p. 31)
vernal equinox
The place on the celestial sphere where the sun crosses the celestial equator moving northward. Also, the time of year when the sun crosses this point, about March 21, and spring begins in the northern hemisphere. (p. 28)
winter solstice
The point on the celestial sphere where the sun is farthest south. Also the time of year when the sun passes this point, about December 22, and winter begins in the northern hemisphere. (p. 28)
A band centered on the ecliptic and encircling the sky. (p. 27)
Chapter 4
center of mass
The balance point of a body or system of masses. The point about which a body or system of masses rotates in the absence of external forces. (p. 69)
circular velocity
The velocity an object needs to stay in orbit around another object. (p. 68)
closed orbit
An orbit that returns to the same starting point over and over. Either a circular orbit or an elliptical orbit. (p. 69)
In the Ptolemaic theory, the large circle around Earth along which the center of the epicycle was thought to move. (p. 51)
eccentricity, e
A number between 1 and 0 that describes the shape of an ellipse. The distance from one focus to the center of the ellipse divided by the semimajor axis. (p. 59)
A closed curve around two points called the foci such that the total distance from one focus to the curve and back to the other focus remains constant. (p. 58)
The small circle followed by a planet in the Ptolemaic theory. The center of the epicycle follows a larger circle (the deferent) around Earth. (p. 51)
In the Ptolemaic theory, the point off center in the deferent from which the center of the epicycle appears to move uniformly. (p. 51)
escape velocity
The initial velocity an object needs to escape from the surface of a celestial body. (p. 69)
geocentric universe
A model universe with Earth at the center, such as the Ptolemaic universe. (p. 50)
geosynchronous satellite
A satellite that orbits eastward around Earth with a period of 24 hours and remains above the same spot on Earth's surface. (p. 68)
heliocentric universe
A model of the universe with the sun at the center, such as the Copernican universe. (p. 49)
A conjecture, subject to further tests, that accounts for a set of facts. (p. 59)
inverse square relation
A rule that the strength of an effect (such as gravity) decreases in proportion as the distance squared increases. (p. 66)
A measure of the amount of matter making up an object. (p. 66)
natural law
A theory that is almost universally accepted as true. (p. 59)
neap tide
Ocean tide of low amplitude occurring at first- and third-quarter moon. (p. 71)
open orbit
An orbit that carries an object away, never to return to its starting point. (p. 69)
A commonly accepted set of scientific ideas and assumptions. (p. 54)
The apparent change in position of an object due to a change in the location of the observer. Astronomical parallax is measured in seconds of arc. (p. 50)
retrograde motion
The apparent backward (westward) motion of planets as seen against the background of stars. (p. 50)
semimajor axis, a
Half of the longest diameter of an ellipse. (p. 58)
spring tide
Ocean tide of high amplitude that occurs at full and new moon. (p. 71)
A system of assumptions and principles applicable to a wide range of phenomena that have been repeatedly verified. (p. 59)
uniform circular motion
The classical belief that the perfect heavens could only move by the combination of uniform motion along circular orbits. (p. 50)
Chapter 5
achromatic lens
A telescope lens composed of two lenses ground from different kinds of glass and designed to bring two selected colors to the same focus and correct for chromatic aberration. (p. 82)
active optics
Thin telescope mirrors that are controlled by computers to maintain proper shape as the telescope moves. (p. 89)
adaptive optics
A computer-controlled optical system used to partially correct for seeing in an astronomical telescope. (p. 89)
alt-azimuth mounting
A telescope mounting that allows the telescope to move in altitude (perpendicular to the horizon) and in azimuth (parallel to the horizon). See also equatorial mounting. (p. 89)
A unit of distance. 1 angstrom = 10-10 m. Commonly used to measure the wavelength of light. (p. 79)
atmospheric window
Wavelength region in which our atmosphere is transparent - at visual, infrared, and radio wavelengths. (p. 80)
binding energy
The energy needed to pull an electron away from its atom. (p. 95)
black body radiation
Radiation emitted by a hypothetical perfect radiator. The spectrum is continuous, and the wavelength of maximum emission depends on the body's temperature. (p. 97)
Cassegrain focus
The optical design in which the secondary mirror reflects light back down the tube through a hole in the center of the objective mirror. (p. 88)
See charge-coupled device.
charge-coupled device (CCD)
An electronic device consisting of a large array of light-sensitive elements used to record very faint images. (p. 90)
chromatic aberration
A distortion found in refracting telescopes because lenses focus different colors at slightly different distances. Images are consequently surrounded by color fringes. (p. 81)
comparison spectrum
A spectrum of known spectral lines used to identify unknown wavelengths in an object's spectrum. (p. 91)
diffraction fringe
Blurred fringe surrounding any image, caused by the wave properties of light. Because of this, no image detail smaller than the fringe can be seen. (p. 83)
electromagnetic radiation
Changing electric and magnetic fields that travel through space and transfer energy from one place to another; examples are light or radio waves. (p. 78)
equatorial mounting
A telescope mounting that allows motion parallel to and perpendicular to the celestial equator. (p. 89)
A short-focal-length lens used to enlarge the image in a telescope. The lens nearest the eye. (p. 80)
false-color image
A representation of graphical data with added or enhanced color to reveal detail. (p. 90)
focal length
The focal length of a lens is the distance from the lens to the point where it focuses parallel rays of light. (p. 80)
A piece of material in which numerous microscopic parallel lines are scribed. Light encountering a grating is dispersed to form a spectrum. (p. 91)
The observing technique in which separated telescopes combine to produce a virtual telescope with the resolution of a much-larger-diameter telescope. (p. 87)
light pollution
The illumination of the night sky by waste light from cities and outdoor lighting, which prevents the observation of faint objects. (p. 84)
light-gathering power
The ability of a telescope to collect light. Proportional to the area of the telescope's objective lens or mirror. (p. 82)
magnifying power
The ability of a telescope to make an image larger. (p. 84)
nanometer (nm)
A unit of distance equaling one-billionth of a meter (10-9 m). (p. 79)
Newtonian focus
The optical design in which a diagonal mirror reflects light out the side of the telescope tube for easier access. (p. 88)
objective lens
In a refracting telescope, the long-focal-length lens that forms an image of the object viewed. The lens closest to the object. (p. 80)
objective mirror
In a reflecting telescope, the principal mirror (reflecting surface) that forms an image of the object viewed. (p. 80)
A quantum of electromagnetic energy. Carries an amount of energy that depends inversely on its wavelength. (p. 78)
polar axis
In an equatorial telescope mounting, the axis that is parallel to Earth's axis. (p. 89)
primary lens
In a refracting telescope, the largest lens. (p. 80)
primary mirror
In a reflecting telescope, the largest mirror. (p. 80)
prime focus
The point at which the objective mirror forms an image in a reflecting telescope. (p. 88)
radio interferometer
Two or more radio telescopes that combine their signals to achieve the resolving power of a larger telescope. (p. 93)
reflecting telescope
A telescope that uses a concave mirror to focus light into an image. (p. 81)
refracting telescope
A telescope that forms images by bending (refracting) light with a lens. (p. 81)
resolving power
The ability of a telescope to reveal fine detail. Depends on the diameter of the telescope objective. (p. 83)
Schmidt-Cassegrain focus
The optical design that uses a thin corrector plate at the entrance to the telescope tube. A popular design for small telescopes. (p. 88)
secondary mirror
In a reflecting telescope, a mirror that directs the light from the primary mirror to a focal position. (p. 88)
Atmospheric conditions on a given night. When the atmosphere is unsteady, producing blurred images, the seeing is said to be poor. (p. 83)
sidereal drive
The motor and gears on a telescope that turn it westward to keep it pointed at a star. (p. 89)
A device that separates light by wavelengths to produce a spectrum. (p. 91)
The distance between successive peaks or troughs of a wave. Usually represented by the Greek letter lambda. (p. 78)
Chapter 6
absolute zero
The theoretical lowest possible temperature at which a material contains no extractable heat energy. Zero on the Kelvin temperature scale. (p. 108)
absorption line
A dark line in a spectrum. Produced by the absence of photons absorbed by atoms or molecules. (p. 110)
absorption spectrum (dark-line spectrum)
A spectrum that contains absorption lines. (p. 110)
Balmer series
A series of spectral lines produced by hydrogen in the near-ultraviolet and visible parts of the spectrum. The three longest-wavelength Balmer lines are visible to the human eye. (p. 111)
blue shift
A Doppler shift toward shorter wavelengths caused by a velocity of approach. (p. 105)
bright-line spectrum
See emission spectrum.
continuous spectrum
A spectrum in which there are no absorption or emission lines. (p. 110)
Coulomb force
The electrostatic force of repulsion or attraction between charged bodies. (p. 105)
dark-line spectrum
See absorption spectrum.
Doppler effect
The change in the wavelength of radiation due to relative radial motion of source and observer. (p. 115)
Low-mass atomic particle carrying a negative charge. (p. 104)
emission line
A bright line in a spectrum caused by the emission of photons from atoms. (p. 110)
emission spectrum (bright-line spectrum)
A spectrum containing emission lines. (p. 110)
energy level
One of a number of states an electron may occupy in an atom, depending on its binding energy. (p. 106)
excited atom
An atom in which an electron has moved from a lower to a higher energy level. (p. 106)
ground state
The lowest permitted electron energy level in an atom. (p. 107)
Energy stored in a material as agitation among its particles. (p. 107)
An atom that has lost or gained one or more electrons. (p. 105)
The process in which atoms lose or gain electrons. (p. 105)
Atoms that have the same number of protons but a different number of neutrons. (p. 105)
joule (J)
A unit of energy equivalent to a force of 1 newton acting over a distance of 1 m. One joule per second equals 1 watt of power. (p. 109)
Kelvin temperature scale
A temperature scale using Celsius degrees and based on zero at absolute zero. (p. 107)
Kirchhoff 's laws
A set of laws that describe the absorption and emission of light by matter. (p. 110)
L dwarf
A main-sequence star cooler than an M star. (p. 114)
Lyman series
Spectral lines in the ultraviolet spectrum of hydrogen produced by transitions whose lowest energy level is the ground state. (p. 111)
Two or more atoms bonded together. (p. 105)
An atomic particle with no charge and about the same mass as a proton. (p. 104)
nucleus (of an atom)
The central core of an atom containing protons and neutrons. Carries a net positive charge. (p. 104)
Paschen series
Spectral lines in the infrared spectrum of hydrogen produced by transitions whose lowest energy level is the third. (p. 111)
permitted orbit
One of the energy levels in an atom that an electron may occupy. (p. 106)
A positively charged atomic particle contained in the nucleus of an atom. The nucleus of a hydrogen atom. (p. 104)
quantum mechanics
The study of the behavior of atoms and atomic particles. (p. 105)
radial velocity (Vr)
That component of an object's velocity directed away from or toward Earth. (p. 116)
A Doppler shift toward longer wavelengths caused by a velocity of recession. (p. 115)
spectral class or type
A star's position in the temperature classification system O, B, A, F, G, K, M. Based on the appearance of the star's spectrum. (p. 113)
spectral line
A line in a spectrum at a specific wavelength produced by the absorption or emission of light by certain atoms. (p. 104)
spectral sequence
The arrangement of spectral classes (O, B, A, F, G, K, M) ranging from hot to cool. (p. 113)
T dwarf
A very cool, low-mass star or brown dwarf located below the L stars on the main sequence. (p. 114)
A measure of the agitation among the atoms and molecules of a material. The intensity of heat. (p. 107)
The movement of an electron from one atomic energy level to another. (p. 111)
wavelength of maximum intensity
The wavelength at which a perfect radiator emits the maximum amount of energy. Depends only on the object's temperature. (p. 108)
Chapter 7
active region
A magnetic region on the solar surface that includes sunspots, prominences, flares, etc. (p. 131)
The glowing light display that results when a planet's magnetic field guides charged particles toward the north and south magnetic poles, where they strike the upper atmosphere and excite atoms to emit photons. (p. 137)
Babcock model
A model of the sun's magnetic cycle in which the differential rotation of the sun winds up and tangles the solar magnetic field in a 22-year cycle. This is thought to be responsible for the 11-year sunspot cycle. (p. 133)
Circulation in a fluid driven by heat. Hot material rises and cool material sinks. (p. 125)
coronal hole
An area of the solar surface that is dark at X-ray wavelengths. Thought to be associated with divergent magnetic fields and the source of the solar wind. (p. 137)
coronal mass ejection (CME)
Matter ejected from the sun's corona in powerful surges guided by magnetic fields. (p. 137)
Coulomb barrier
The electrostatic force of repulsion between bodies of like charge. Commonly applied to atomic nuclei. (p. 138)
An isotope of hydrogen in which the nucleus contains a proton and a neutron. (p. 139)
differential rotation
The rotation of a body in which different parts of the body have different periods of rotation. This is true of the sun, the Jovian planets, and the disk of the galaxy. (p. 132)
dynamo effect
The process by which a rotating, convecting body of conducting matter, such as Earth's core, can generate a magnetic field. (p. 132)
A solar prominence seen from above silhouetted against the bright photosphere. (p. 126)
A photograph (usually of the sun) taken in the light of a specific region of the spectrum - for example, an H-alpha filtergram. (p. 126)
A violent eruption on the sun's surface. (p. 137)
The fine structure of bright grains covering the sun's surface. (p. 125)
The study of the interior of the sun by the analysis of its modes of vibration. (p. 128)
magnetic carpet
The network of small magnetic loops that covers the solar surface. (p. 127)
Maunder butterfly diagram
A graph showing the latitude of sunspots versus time. First plotted by W. W. Maunder in 1904. (p. 130)
Maunder minimum
A period of less numerous sunspots and other solar activity between 1645 and 1715. (p. 131)
A neutral, massless atomic particle that travels at or nearly at the speed of light. (p. 139)
nuclear fission
Reactions that break the nuclei of atoms into fragments. (p. 135)
nuclear fusion
Reactions that join the nuclei of atoms to form more massive nuclei. (p. 135)
proton-proton chain
A series of three nuclear reactions that builds a helium atom by adding together protons. The main energy source in the sun. (p. 139)
On the sun, the merging of magnetic fields to release energy in the form of flares. (p. 137)
solar wind
Rapidly moving atoms and ions that escape from the solar corona and blow outward through the solar system. (p. 127)
A small, flamelike projection in the chromosphere of the sun. (p. 126)
strong force
One of the four forces of nature. The strong force binds protons and neutrons together in atomic nuclei. (p. 135)
Relatively dark spot on the sun that contains intense magnetic fields. (p. 124)
Very large convective features in the sun's surface. (p. 127)
weak force
One of the four forces of nature. The weak force is responsible for some forms of radioactive decay. (p. 135)
Zeeman effect
The splitting of spectral lines into multiple components when the atoms are in a magnetic field. (p. 131)
Chapter 8
absolute visual magnitude (Mv)
Intrinsic brightness of a star. The apparent visual magnitude the star would have if it were 10 pc away. (p. 149)
binary stars
Pairs of stars that orbit around their common center of mass. (p. 157)
bipolar flow
Jets of gas flowing away from a central object in opposite directions. Usually applied to protostars. (p. 167)
birth line
In the H-R diagram, the line above the main sequence where protostars first become visible. (p. 165)
Bok globule
Small, dark cloud only about 1 ly in diameter that contains 10 to 1000 solar masses of gas and dust. Believed to be related to star formation. (p. 166)
eclipsing binary system
A binary star system in which the stars eclipse each other. (p. 160)
A measure of the flow of energy out of a surface. Usually applied to light. (p. 149)
Large, cool, highly luminous star in the upper right of the H-R diagram. Typically 10 to 100 times the diameter of the sun. (p. 152)
H-R diagram
See Hertzsprung-Russell diagram.
Hertzsprung-Russell (H-R) diagram
A plot of the intrinsic brightness versus the surface temperature of stars. It separates the effects of temperature and surface area on stellar luminosity. Commonly plotted as absolute magnitude versus spectral type but also as luminosity versus surface temperature or color. (p. 151)
light curve
A graph of brightness versus time commonly used in analyzing variable stars and eclipsing binaries. (p. 160)
luminosity (L)
The total amount of energy a star radiates in 1 second. (p. 149)
luminosity class
A category of stars of similar luminosity, determined by the widths of lines in their spectra. (p. 153)
main sequence
The region of the H-R diagram running from upper left to lower right, which includes roughly 90 percent of all stars. (p. 152)
mass-luminosity relation
The more massive a star is, the more luminous it is. (p. 162)
parsec (pc)
The distance to a hypothetical star whose parallax is 1 second of arc. 1 pc = 206,265 AU = 3.26 ly. (p. 147)
red dwarf
A faint, cool, low-mass, main sequence star. (p. 153)
spectroscopic binary system
A star system in which the stars are too close together to be visible separately. We see a single point of light, and only by taking a spectrum can we determine that there are two stars. (p. 158)
spectroscopic parallax
The method of determining a star's distance by comparing its apparent magnitude with its absolute magnitude as estimated from its spectrum. (p. 154)
stellar parallax (p)
A measure of stellar distance. See also parallax. (p. 147)
Exceptionally luminous star whose diameter is 10 to 1000 times that of the sun. (p. 152)
visual binary system
A binary star system in which the two stars are separately visible in the telescope. (p. 156)
white dwarf
Dying star that has collapsed to the size of Earth and is slowly cooling off. At the lower left of the H-R diagram. (p. 153)
Chapter 9
Group of widely scattered stars (10 to 100) moving together through space. Not gravitationally bound into clusters. (p. 180)
brown dwarf
A star whose mass is too low to ignite nuclear fusion. Heated by contraction. (p. 192)
carbon-nitrogen-oxygen (CNO) cycle
A series of nuclear reactions that use carbon as a catalyst to combine four hydrogen atoms to make one helium atom plus energy. Effective in stars more massive than the sun. (p. 183)
CNO cycle
See carbon-nitrogen-oxygen cycle.
conservation of energy
One of the basic laws of stellar structure. The amount of energy flowing out of the top of a shell must equal the amount coming in at the bottom plus whatever energy is generated within the shell. (p. 187)
conservation of mass
One of the basic laws of stellar structure. The total mass of the star must equal the sum of the masses of the shells, and the mass must be distributed smoothly through the star. (p. 187)
dark nebula
A cloud of gas and dust seen silhouetted against a brighter nebula. (p. 177)
emission nebula
A cloud of glowing gas excited by ultraviolet radiation from hot stars. (p. 176)
energy transport
Flow of energy from hot regions to cooler regions by one of three methods: conduction, convection, or radiation. (p. 188)
evolutionary track
The path a star follows in the H-R diagram as it gradually changes its surface temperature and luminosity. (p. 180)
H II region
A region of ionized hydrogen around a hot star. (p. 176)
Herbig-Haro object
A small nebula that varies irregularly in brightness. Believed to be associated with star formation. (p. 185)
hydrostatic equilibrium
The balance between the weight of the material pressing downward on a layer in a star and the pressure in that layer. (p. 187)
infrared cirrus
Wispy network of cold dust clouds discovered by the Infrared Astronomy Satellite. (p. 178)
interstellar dust
Microscopic solid grains in the interstellar medium. (p. 174)
interstellar medium
The gas and dust distributed between the stars. (p. 174)
interstellar reddening
The process in which dust scatters blue light out of starlight and makes the stars look redder. (p. 174)
molecular cloud
A dense interstellar gas cloud in which atoms are able to link together to form molecules such as H2 and CO. (p. 179)
A glowing cloud of gas or a cloud of dust reflecting the light of nearby stars. (p. 175)
The resistance of a gas to the passage of radiation. (p. 189)
A collapsing cloud of gas and dust destined to become a star. (p. 180)
reflection nebula
A nebula produced by starlight reflecting off dust particles in the interstellar medium. (p. 176)
shock wave
A sudden change in pressure that travels as an intense sound wave. (p. 179)
stellar model
A table of numbers representing the conditions in various layers within a star. (p. 189)
T Tauri star
A young star surrounded by gas and dust. Believed to be contracting toward the main sequence. (p. 184)
triple-alpha process
The nuclear fusion process that combines three helium nuclei (alpha particles) to make one carbon nucleus. (p. 186)
zero-age main sequence (ZAMS)
The location in the H-R diagram where stars first reach stability as hydrogen-burning stars. (p. 193)
Chapter 10
accretion disk
The whirling disk of gas that forms around a compact object such as a white dwarf, neutron star, or black hole as matter is drawn in. (p. 216)
angular momentum
A measure of the tendency of a rotating body to continue rotating. Mathematically, the product of mass, velocity, and radius. (p. 215)
black dwarf
The end state of a white dwarf that has cooled to low temperature. (p. 211)
Chandrasekhar limit
The maximum mass of a white dwarf, about 1.4 solar masses. A white dwarf of greater mass cannot support itself and will collapse. (p. 211)
degenerate matter
Extremely high-density matter in which pressure no longer depends on temperature due to quantum mechanical effects. (p. 204)
globular cluster
A star cluster containing 100,000 to 1 million stars in a sphere about 75 ly in diameter. Generally old, metal-poor, and found in the spherical component of the galaxy. (p. 208)
helium flash
The explosive ignition of helium burning that takes place in some giant stars. (p. 205)
horizontal branch
In the H-R diagram, stars fusing helium in a shell and evolving back toward the red giant region. (p. 209)
inner Lagrangian point
The point of gravitational equilibrium between two orbiting stars through which matter can flow from one star to the other. (p. 214)
Lagrangian points
Points of gravitational stability in the orbital plane of a binary star system, planet, or moon. (p. 214)
From the Latin, meaning "new," a sudden brightening of a star making it appear as a new star in the sky. Believed to be associated with eruptions on white dwarfs in binary systems. (p. 200)
open cluster
A cluster of 100 to 1000 stars with an open, transparent appearance. The stars are not tightly grouped. Usually relatively young and located in the disk of the galaxy. (p. 208)
planetary nebula
An expanding shell of gas ejected from a star during the latter stages of its evolution. (p. 207)
Roche lobe
The volume of space a star controls gravitationally within a binary system. (p. 214)
Roche surface
The dumbbell-shaped surface that encloses the Roche lobes around a close binary star. (p. 214)
The explosion of a star in which it increases its brightness by a factor of about a million. (p. 200)
supernova remnant
The expanding shell of gas marking the site of a supernova explosion. (p. 222)
synchrotron radiation
Radiation emitted when high-speed electrons move through a magnetic field. (p. 220)
turnoff point
The point in an H-R diagram at which a cluster's stars turn off of the main sequence and move toward the red-giant region, revealing the approximate age of the cluster. (p. 208)
type I supernova
A supernova explosion caused by the collapse of a white dwarf. (p. 220)
type II supernova
A supernova explosion caused by the collapse of a massive star. (p. 219)
Chapter 11
black hole
A mass that has collapsed to such a small volume that its gravity prevents the escape of all radiation. Also, the volume of space from which radiation may not escape. (p. 240)
A star of high mass that collapses into a black hole. A possible source of gamma-ray bursts. (p. 247)
event horizon
The boundary of the region of a black hole from which no radiation may escape. No event that occurs within the event horizon is visible to a distant observer. (p. 242)
gamma-ray burster
An object very faint at visual wavelengths that produces a sudden, powerful burst of gamma rays. (p. 246)
gravitational radiation
Disturbances in a gravitational field traveling at the velocity of light and carrying energy away from an object with a rapidly changing mass distribution. (p. 236)
gravitational redshift
The lengthening of the wavelength of a photon due to its escape from a gravitational field. (p. 243)
Produced when a very massive star collapses into a black hole. Thought to be a possible source of gamma-ray bursts. (p. 247)
A class of neutron star having very strong magnetic fields. (p. 247)
millisecond pulsar
A pulsar with a pulse period of only a few milliseconds. (p. 238)
neutron star
A small, highly dense star composed almost entirely of tightly packed neutrons. Radius about 10 km. (p. 230)
A source of short, precisely timed radio bursts. Believed to be spinning neutron stars. (p. 231)
pulsar wind
The breeze of high-energy particles flowing away from a spinning neutron star. (p. 233)
Schwarzschild radius (RS)
The radius of the event horizon around a black hole. (p. 242)
The object of zero radius into which the matter in a black hole is believed to fall. (p. 241)
soft gamma-ray repeater (SGR)
An object that produces repeated bursts of low-energy (soft) gamma rays. (p. 247)
time dilation
The slowing of moving clocks or clocks in strong gravitational fields. (p. 243)
X-ray burster
An object that produces repeated bursts of X rays. (p. 237)
Chapter 12
The establishment of the relationship between a parameter that is easily determined and a parameter that is more difficult to determine. For example, the periods of Cepheid variables have been calibrated to reveal absolute magnitudes, which can then be used to find distance. Thus astronomers say Cepheids have been calibrated as distance indicators. (p. 258)
Cepheid variable star
Variable star with a period of 60 days. Period of variation is related to luminosity. (p. 255)
dark halo
The low-density extension of the halo of our galaxy believed to be composed of dark matter. (p. 263)
dark matter
Nonluminous matter that is detected only by its gravitational influence. (p. 263)
density wave theory
Theory proposed to account for spiral arms as compressions of the interstellar medium in the disk of the galaxy. (p. 270)
differential rotation
The rotation of a body in which different parts of the body have different periods of rotation. This is true of the sun, the Jovian planets, and the disk of the galaxy. (p. 262)
disk component
All material confined to the plane of the galaxy. (p. 260)
Describes a galaxy whose spiral arms have a woolly or fluffy appearance. (p. 272)
galactic corona
The extended, spherical distribution of low-luminosity matter believed to surround the Milky Way and other galaxies. (p. 263)
The spherical region of a spiral galaxy, containing a thin scattering of stars, star clusters, and small amounts of gas. (p. 261)
instability strip
The region of the H-R diagram in which stars are unstable to pulsation. A star passing through this strip becomes a variable star. (p. 255)
kiloparsec (kpc)
A unit of distance equal to 1000 pc or 3260 ly. (p. 260)
Local Group
The small cluster of a few dozen galaxies that contains our Milky Way Galaxy. (p. 267)
In astronomical usage, all atoms heavier than helium. (p. 264)
nuclear bulge
The spherical cloud of stars that lies at the center of spiral galaxies. (p. 261)
period-luminosity relation
The relation between period of pulsation and intrinsic brightness among Cepheid variable stars. (p. 256)
population I
Stars rich in atoms heavier than helium. Nearly always relatively young stars found in the disk of the galaxy. (p. 264)
population II
Stars poor in atoms heavier than helium. Nearly always relatively old stars found in the halo, globular clusters, or the nuclear bulge. (p. 264)
proper motion
The rate at which a star moves across the sky. Measured in seconds of arc per year. (p. 258)
rotation curve
A graph of orbital velocity versus radius in the disk of a galaxy. (p. 262)
RR Lyrae variable star
Variable star with period of from 12 to 24 hours. Common in some globular clusters. (p. 255)
Sagittarius A*
The powerful radio source located at the core of the Milky Way Galaxy. (p. 273)
self-sustaining star formation
The process by which the birth of stars compresses the surrounding gas clouds and triggers the formation of more stars. Proposed to explain spiral arms. (p. 272)
Shapley-Curtis debate
A 1920 debate between Harlow Shapley and Heber Curtis on the nature of spiral nebulae. Curtis argued that they are other galaxies, and Shapley argued they are internal to our own galaxy. (p. 259)
spherical component
The part of the galaxy including all matter in a spherical distribution around the center (the halo and nuclear bulge). (p. 261)
spiral arm
Long spiral pattern of bright stars, star clusters, gas, and dust. Spiral arms extend from the center to the edge of the disk of spiral galaxies. (p. 260)
spiral tracer
Object used to map the spiral arms - for example, O and B associations, open clusters, clouds of ionized hydrogen, and some types of variable stars. (p. 268)
variable star
A star whose brightness changes periodically. (p. 255)
Chapter 13
barred spiral galaxy
A spiral galaxy with an elongated nucleus resembling a bar from which the arms originate. (p. 284)
cluster method
The method of determining the masses of galaxies based on the motions of galaxies in a cluster. (p. 291)
distance indicator
Object whose luminosity or diameter is known. Used to find the distance to a star cluster or galaxy. (p. 287)
elliptical galaxy
A galaxy that is round or elliptical in outline and contains little gas and dust, no disk or spiral arms, and few hot, bright stars. (p. 284)
galactic cannibalism
The theory that large galaxies absorb smaller galaxies. (p. 296)
gravitational lensing
The process by which the gravitational field of a massive object focuses the light from a distant object to produce multiple images of the distant object or to make the distant object look brighter. (p. 293)
Hubble constant (H)
A measure of the rate of expansion of the universe. The average value of velocity of recession divided by distance. Presently believed to be about 70 km/s/Mpc. (p. 290)
Hubble law
The linear relation between the distances to galaxies and their velocity of recession. (p. 290)
irregular galaxy
A galaxy with a chaotic appearance, large clouds of gas and dust, and both population I and II stars, but without spiral arms. (p. 285)
Large Magellanic Cloud
An irregular galaxy that is a satellite of our Milky Way Galaxy. It is visible in the southern sky. (p. 285)
look-back time
The amount by which we look into the past when we look at a distant galaxy. A time equal to the distance to the galaxy in light-years. (p. 288)
megaparsec (Mpc)
A unit of distance equal to 1,000,000 pc. (p. 287)
poor galaxy cluster
An irregularly shaped cluster that contains fewer than 1000 galaxies, many spiral, and no giant ellipticals. (p. 295)
rich galaxy cluster
A cluster containing over 1000 galaxies, mostly elliptical, scattered over a volume about 3 Mpc in diameter. (p. 295)
ring galaxy
A galaxy that resembles a ring around a bright nucleus. Believed to be the result of a head-on collision of two galaxies. (p. 297)
rotation curve method
A method of determining a galaxy's mass by observing the orbital velocity and radius of stars in the galaxy. (p. 291)
Small Magellanic Cloud
An irregular galaxy that is a satellite of our Milky Way Galaxy. It is visible in the southern sky. (p. 285)
spiral galaxy
A galaxy with an obvious disk component containing gas; dust; hot, bright stars; and spiral arms. (p. 284)
starburst galaxy
A galaxy undergoing a rapid burst of star formation. (p. 299)
tidal tail
A long streamer of stars, gas, and dust torn from a galaxy during its close interaction with another passing galaxy. (p. 296)
velocity dispersion method
A method of finding a galaxy's mass by observing the range of velocities within the galaxy. (p. 291)
Chapter 14
active galactic nuclei (AGN)
The centers of active galaxies that are emitting large amounts of excess energy. See also active galaxy. (p. 306)
active galaxy
A galaxy whose center emits large amounts of excess energy, often in the form of radio emission. Active galaxies are suspected of having massive black holes in their centers into which matter is flowing. (p. 306)
BL Lac objects
Objects that resemble quasars. Thought to be highly luminous cores of distant active galaxies. (p. 313)
See BL Lac objects.
cold dark matter
Mass in the universe, as yet undetected except for its gravitational influence, which is made up of slow-moving particles. (p. 311)
double-exhaust model
The theory that double radio lobes are produced by pairs of jets emitted in opposite directions from the centers of active galaxies. (p. 308)
double-lobed radio source
A galaxy that emits radio energy from two regions (lobes) located on opposite sides of the galaxy. (p. 308)
hot spot
In geology, a place on Earth's crust where volcanism is caused by a rising convection cell in the mantle below. In radio astronomy, a bright spot in a radio lobe. (p. 310)
quasar (quasi-stellar object, or QSO)
Small, powerful sources of energy believed to be the active cores of very distant galaxies. (p. 315)
radio galaxy
A galaxy that is a strong source of radio signals. (p. 304)
Seyfert galaxy
An otherwise normal spiral galaxy with an unusually bright, small core that fluctuates in brightness. Believed to indicate the core is erupting. (p. 306)
unified model
An attempt to explain the different types of active galactic nuclei using a single model viewed from different directions. (p. 313)
Chapter 15
Matter composed of antiparticles, which upon colliding with a matching particle of normal matter annihilate and convert the mass of both particles into energy. The antiproton is the antiparticle of the proton, and the positron is the antiparticle of the electron. (p. 333)
big bang
The high-density, high-temperature state from which the expanding universe of galaxies began. (p. 329)
big rip
The fate of the universe if dark energy increases with time and galaxies, stars, and even atoms are eventually ripped apart by the accelerating expansion of the universe. (p. 346)
closed universe
A model universe in which the average density is great enough to stop the expansion and make the universe contract. (p. 339)
cosmic microwave background radiation
Radiation from the hot clouds of the big bang explosion. The large red shift makes it appear to come from a body whose temperature is only 2.7 K. (p. 333)
cosmological constant
A constant in Einstein's equations of space and time that represents a force of repulsion. (p. 345)
cosmological principle
The assumption that any observer in any galaxy sees the same general features of the universe. (p. 336)
The study of the nature, origin, and evolution of the universe. (p. 326)
critical density
The average density of the universe needed to make its curvature flat. (p. 337)
dark age
The period of time after the glow of the big bang faded into the infrared and before the birth of the first stars, during which the universe expanded in darkness. (p. 334)
dark energy
The energy believed to fill empty spaces and drive the accelration of the expanding universe. (p. 345)
flat universe
A model of the universe in which space-time is not curved. (p. 339)
flatness problem
In cosmology, the peculiar circumstance that the early universe must have contained almost exactly the right amount of matter to make space-time flat. (p. 343)
grand unified theories (GUTs)
Theories that attempt to unify (describe in a similar way) the electromagnetic, weak, and strong forces of nature. (p. 343)
See grand unified theories.
The assumption that, on the large scale, matter is uniformly spread through the universe. (p. 336)
horizon problem
In cosmology, the circumstance that the primordial background radiation seems much more isotropic than can be explained by the standard big bang theory. (p. 343)
hot dark matter
Dark matter made up of particles such as neutrinos traveling at or nearly at the speed of light. (p. 342)
Hubble time
The age of the universe, equivalent to 1 divided by the Hubble constant. The Hubble time is the age of the universe if it has expanded since the big bang at a constant rate. (p. 330)
inflationary universe
A version of the big bang theory that includes a rapid expansion when the universe was very young. Derived from grand unified theories. (p. 343)
The assumption that in its general properties the universe looks the same in every direction. (p. 336)
large-scale structure
The distribution of clusters and superclusters of galaxies in filaments and walls enclosing voids. (p. 346)
Massive compact halo objects. Low-luminosity objects such as planets and brown dwarfs that contribute to the mass of the halo. (p. 342)
nonbaryonic matter
Proposed dark matter made up of particles other than protons and neutrons (baryons). (p. 341)
observable universe
The part of the universe that we can see from our location in space and in time. (p. 328)
Olbers' paradox
The conflict between observation and theory about why the night sky should or should not be dark. (p. 326)
open universe
A model of the universe in which the average density is less than the critical density needed to halt the expansion. (p. 339)
oscillating universe theory
The theory that the universe begins with a big bang, expands, is slowed by its own gravity, and then falls back to create another big bang. (p. 340)
The postulated energy that fills empty space and drives the acceleration of the universe. (p. 345)
The stage within 300,000 years of the big bang, when the gas became transparent to radiation. (p. 334)
The stage in the early history of the universe when ultraviolet photons from the first stars ionized the gas filling space. (p. 334)
steady-state theory
The theory (now generally abandoned) that the universe does not evolve. (p. 333)
A cluster of galaxy clusters. (p. 346)
Chapter 16
The sticking together of solid particles to produce a larger particle. (p. 370)
The ratio of the light reflected from an object divided by the light that hits the object. Albedo equals 0 for perfectly black and 1 for perfectly white. (p. 353)
Small, rocky world. Most asteroids lie between Mars and Jupiter in the asteroid belt. (p. 363)
Rock composed of fragments of earlier rocks bonded together. (p. 353)
One of the small, icy bodies that orbit the sun and produce tails of gas and dust when they approach the sun. (p. 363)
The growth of a particle by addition of material from surrounding gas, atom by atom. (p. 369)
condensation sequence
The sequence in which different materials condense from the solar nebula as we move outward from the sun. (p. 369)
The separation of planetary material according to density. (p. 371)
extrasolar planet
A planet orbiting a star other than the sun. (p. 359)
Galilean satellites
The four largest satellites of Jupiter, named after their discoverer Galileo. (p. 365)
gravitational collapse
The process by which a forming body such as a planet gravitationally captures gas from its surroundings. (p. 368)
The time required for half of the atoms in a radioactive sample to decay. (p. 366)
heat of formation
In planetology, the heat released by in-falling matter during the formation of a planetary body. (p. 372)
heavy bombardment
The intense cratering during the first 0.5 billion years in the history of the solar system. (p. 375)
Jovian planet
Jupiterlike planet with a large diameter and low density. (p. 364)
A small bit of matter heated by friction to incandescent vapor as it falls into Earth's atmosphere. (p. 366)
A meteor that survives its passage through the atmosphere and strikes the ground. (p. 366)
A meteor in space before it enters Earth's atmosphere. (p. 366)
The release of gases from a planet's interior. (p. 372)
One of the small bodies that formed from the solar nebula and eventually grew into protoplanets. (p. 369)
Massive object resulting from the coalescence of planetesimals in the solar nebula and destined to become a planet. (p. 370)
radiation pressure
The force exerted on the surface of a body by its absorption of light. Small particles floating in the solar system can be blown outward by the pressure of the sunlight. (p. 374)
solar nebula theory
The theory that the planets formed from the same cloud of gas and dust that formed the sun. (p. 356)
terrestrial planet
An Earthlike planet - small, dense, rocky. (p. 364)
uncompressed density
The density a planet would have if its gravity did not compress it. (p. 368)
Chapter 17
Rock of aluminum and calcium silicates found in the lunar highlands. (p. 391)
Dark igneous rock characteristic of solidified lava. (p. 384)
capture hypothesis
The theory that Earth's moon formed elsewhere in the solar nebula and was later captured by Earth. (p. 394)
comparative planetology
The study of planets in relation to one another. (p. 378)
composite volcano
A volcano formed by successive lava and ash flows. They have steep sides and, on Earth, are found along subduction zones. (p. 400)
condensation hypothesis
The theory that Earth and the moon condensed from the same cloud of material in roughly their present orbital relationship. (p. 394)
On Venus, large, round geological faults in the crust caused by the intrusion of magma below the crust. (p. 402)
Pulverized rock scattered by meteorite impacts on a planetary surface. (p. 388)
fission hypothesis
The theory that the moon and Earth formed when a rapidly rotating protoplanet split into two pieces. (p. 394)
folded mountain range
A long range of mountains formed by the compression of a planet's crust. (p. 384)
global warming
The gradual increase in the surface temperature of Earth caused by human modifications to Earth's atmosphere. (p. 386)
greenhouse effect
The process by which a carbon dioxide atmosphere traps heat and raises the temperature of a planetary surface. (p. 386)
large-impact hypothesis
The theory that the moon formed from debris ejected during a collision between Earth and a large planetesimal. (p. 394)
lobate scarp
A curved cliff such as those found on Mercury. (p. 396)
The layer of dense rock and metal oxides that lies between the molten core and Earth's surface. Also, similar layers in other planets. (p. 381)
One of the lunar lowlands filled by successive flows of dark lava. From the Latin for "sea." (p. 387)
Meteorite of microscopic size. (p. 389)
midocean rise
One of the undersea mountain ranges that push up from the seafloor in the center of the oceans. (p. 384)
multiringed basin
Large impact feature (crater) containing two or more concentric rims formed by fracturing of the planetary crust. (p. 389)
outflow channel
Geological feature produced by the rapid motion of floodwaters. Applied to features on Mars. (p. 409)
P wave
A pressure wave. A type of seismic wave produced in Earth by the compression of the material. (p. 382)
A material with the properties of a solid but capable of flowing under pressure. (p. 383)
plate tectonics
The constant destruction and renewal of Earth's surface by the motion of sections of crust. (p. 395)
primeval atmosphere
Earth's first air. (p. 386)
Ejecta from meteorite impacts forming white streamers radiating from some lunar craters. (p. 388)
rift valley
A long, straight, deep valley produced by the separation of crustal plates. (p. 385)
S wave
A shear wave. A type of seismic wave produced in Earth by the lateral motion of the material. (p. 382)
secondary atmosphere
The gases outgassed from a planet's interior; rich in carbon dioxide. (p. 386)
secondary crater
Impact crater formed by debris ejected from a larger impact. (p. 388)
shield volcano
Wide, low-profile volcanic cone produced by highly liquid lava. (p. 400)
subduction zone
A region of a planetary crust where a tectonic plate slides downward. (p. 384)
The dividing line between daylight and darkness on a planet or moon. (p. 387)
valley network
A system of dry drainage channels on Mars that resembles the beds of rivers and tributary streams on Earth. (p. 409)
vesicular basalt
A porous rock formed by solidified lava with trapped bubbles. (p. 391)
Chapter 18
belt-zone circulation
The atmospheric circulation typical of Jovian planets. Dark belts and bright zones encircle the planet parallel to its equator. (p. 421)
forward scattering
The optical property of finely divided particles to preferentially direct light in the original direction of the light's travel. (p. 425)
gossamer rings
Jupiter's largest and most tenuous rings of dust. (p. 428)
grooved terrain
Regions of the surface of Ganymede consisting of parallel grooves. Believed to have formed by repeated fracture of the icy crust. (p. 428)
Kuiper belt
The collection of icy planetesimals believed to orbit in a region from just beyond Neptune out to 100 AU or more. (p. 446)
liquid metallic hydrogen
A form of liquid hydrogen that is a good electrical conductor, found in the interiors of Jupiter and Saturn. (p. 422)
The volume of space around a planet within which the motion of charged particles is dominated by the planetary magnetic field rather than the solar wind. (p. 422)
The flattening of a spherical body. Usually caused by rotation. (p. 432)
The passage of a larger body in front of a smaller body. (p. 439)
The oval features found on Miranda, a satellite of Uranus. (p. 439)
One of the icy Kuiper belt objects that, like Pluto, are caught in a 3:2 orbital resonance with Neptune. (p. 447)
Roche limit
The minimum distance between a planet and a satellite that holds itself together by its own gravity. If a satellite's orbit brings it within its planet's Roche limit, tidal forces will pull the satellite apart. (p. 425)
shepherd satellite
A satellite that, by its gravitational field, confines particles to a planetary ring. (p. 435)
tidal heating
The heating of a planet or satellite because of friction caused by tides. (p. 430)
Chapter 19
Stony meteorite containing no chondrules or volatiles. (p. 455)
carbonaceous chondrite
Stony meteorite that contains both chondrules and volatiles. These chondrites may be the least-altered remains of the solar nebula still present in the solar system. (p. 455)
A stony meteorite that contains chondrules. (p. 455)
Round, glassy body found in some stony meteorites. Believed to have solidified very quickly from molten drops of silicate material. (p. 455)
The glowing head of a comet. (p. 464)
dust tail
A comet tail composed of dust released from the nucleus and pushed away by the pressure of sunlight. Also known as a type II tail. (p. 464)
gas tail
A comet tail composed of ionized gas atoms released from the nucleus and carried outward by the solar wind. Also called a type I comet tail. (p. 464)
meteor shower
A multitude of meteors that appear to come from the same region of the sky. Believed to be caused by comet debris. (p. 456)
Oort cloud
The hypothetical source of comets. A swarm of icy bodies believed to lie in a spherical shell extending to 100,000 AU from the sun. (p. 462)
stony-iron meteorite
A meteorite composed of stone and iron mixed together. (p. 455)
type I comet tail
See gas tail.
type II comet tail
See dust tail.
Widmanstatten pattern
Bands in iron meteorites due to large crystals of nickel-iron alloys. (p. 455)
Chapter 20
amino acid
Carbon-chain molecule that is the building block of protein. (p. 476)
Cambrian period
A geological period 0.6 to 0.5 billion years ago during which life on Earth became diverse and complex. Cambrian rocks contain the oldest easily identifiable fossils. (p. 478)
chemical evolution
The chemical process that led to the growth of complex molecules on primitive Earth. This did not involve the reproduction of molecules. (p. 480)
A body within a living cell that contains genetic information responsible for the determination and transmission of hereditary traits. (p. 477)
deoxyribonucleic acid
The long carbon-chain molecule that records information to govern the biological activity of the organism. DNA carries the genetic data passed to offspring. (p. 476)
See deoxyribonucleic acid.
Drake equation
The equation that estimates the total number of communicative civilizations in our galaxy. (p. 490)
Special protein that controls processes in an organism. (p. 476)
A unit of DNA - or sometimes RNA - information responsible for controlling an inherited physiological trait. (p. 477)
life zone
A region around a star within which a planet can have temperatures that permit the existence of liquid water. (p. 486)
Miller experiment
An experiment that reproduced the conditions under which life began on Earth and manufactured amino acids and other organic compounds. (p. 478)
Offspring born with altered DNA. (p. 475)
natural selection
The process by which the best traits are passed on, allowing the most able to survive. (p. 475)
primordial soup
The rich solution of organic molecules in Earth's first oceans. (p. 480)
Complex molecule composed of amino acid units. (p. 476)
ribonucleic acid
Long carbon-chain molecules that use the information stored in DNA to manufacture complex molecules necessary to the organism. (p. 477)
See ribonucleic acid.
The Search for Extra-Terrestrial Intelligence. (p. 489)
A layered fossil formation caused by ancient mats of algae or bacteria, which build up mineral deposits season after season. (p. 481)
water hole
The interval of the radio spectrum between the 21-cm hydrogen radiation and the 18-cm OH radiation. Likely wavelengths to use in the search for extraterrestrial life. (p. 489)