| Terms |
Definitions |
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irregular galaxy
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a galaxy that lacks syymmetry
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elleptical galaxy
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galaxy that is round or elliptical in outline. It contains little gas and dust, no disk or spiral arms, and few hot, bright stars
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degenerate matter
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atoms of the matter have squeezed together so tight that the material takes up less space than normaL
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supernova
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an exploding star that increases in brightness many thousands of times
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neutron star
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a star of extremely hight density composed enirely of neutrons
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nova
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a star that explosively increases in brightness
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white dwarf
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a star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size; beliced to be near its final stage of evolution
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Local Group
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the cluster of 20 or so galaxies to which our galaxy belongs
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Hertzsprung-Russell diagram
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Shows stellar evolution
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spiral galaxy
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a flattened, rotating galaxy with pinwheel-like arms of interstellar material and young stars winding out from its nucleus
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planetary nebula
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a shell of incandescent gas expanding from a star
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hydrogen burning
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the conversion of hydrogen through fusion to form helium
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Absolute magnitude
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The true brightness of the stars
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bright nebula
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cloud of glowing has excited by ultraviolet radiation from hot stars
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apparents magnitude
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classified according to brightness
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main-sequence stars
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a sequence of stars on the Hertzsprung-Russel diagram, containing the majority of stars, that runs diagonally from the upper left to the lower right
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stellar parallax
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a measure of stellar distance
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pulsating variables
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a variable starthat pulsates in size and luminosity
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Hubble's law
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relates the distance to a galaxy and its velocity
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big bang
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theory that proposes that the universe originated as a single mass, which subswquently exploded
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interstellar dust
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reflection nebulae are thought to be composed of rather dense clouds of large particles
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magnitude
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a number given to a celestial obfect to express its relative brightness
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emission nebula
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gaseous nebula that derives its visible light from the fluorescence of ultraviolet light from a star in or near the nebula
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light-year
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the distance that light travels in a year; about six trillion miles
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dark nebula
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cloud of interstellar dust that obscures the light of more distant stars and a ppears as an opaque curtain
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protostar
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a collapsing cloud of gas and dust destined to become a star
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galactic cluster
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a system of galaxies containing from several to thousands of member galaxies
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barred spiral galaxy
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galaxy having straight arms extinding from its nucleus
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supergiant
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a very large star of high luminosity
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pulsar
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a variable radio source of small size that emits radio pulses in very regular periods
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nebula
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a cloud of interstellar gas and/ or dust
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eruptive variable
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star that varies in brightness
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reflection nebula
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a relatively dense cloud in interstellar space that is illuminated by starlight
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red giant
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a large, cool star of high luminosity; a star occupying the upper- right portion of the Hertzsprung-Russel diagram
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black hole
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massive tar that has collapsed to such a small volume that its gravity prevents the escape of all radiation
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