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21 Cards in this Set
- Front
- Back
barred spiral galaxy
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A spiral galaxy with an elongated nucleus resembling a bar from which the arms originate. (p. 284)
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cluster method
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The method of determining the masses of galaxies based on the motions of galaxies in a cluster. (p. 291)
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distance indicator
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Object whose luminosity or diameter is known. Used to find the distance to a star cluster or galaxy. (p. 287)
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elliptical galaxy
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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)
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galactic cannibalism
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The theory that large galaxies absorb smaller galaxies. (p. 296)
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gravitational lensing
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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)
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Hubble constant (H)
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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)
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Hubble law
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The linear relation between the distances to galaxies and their velocity of recession. (p. 290)
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irregular galaxy
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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)
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Large Magellanic Cloud
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An irregular galaxy that is a satellite of our Milky Way Galaxy. It is visible in the southern sky. (p. 285)
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look-back time
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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)
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megaparsec (Mpc)
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A unit of distance equal to 1,000,000 pc. (p. 287)
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poor galaxy cluster
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An irregularly shaped cluster that contains fewer than 1000 galaxies, many spiral, and no giant ellipticals. (p. 295)
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rich galaxy cluster
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A cluster containing over 1000 galaxies, mostly elliptical, scattered over a volume about 3 Mpc in diameter. (p. 295)
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ring galaxy
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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)
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rotation curve method
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A method of determining a galaxy's mass by observing the orbital velocity and radius of stars in the galaxy. (p. 291)
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Small Magellanic Cloud
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An irregular galaxy that is a satellite of our Milky Way Galaxy. It is visible in the southern sky. (p. 285)
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spiral galaxy
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A galaxy with an obvious disk component containing gas; dust; hot, bright stars; and spiral arms. (p. 284)
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starburst galaxy
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A galaxy undergoing a rapid burst of star formation. (p. 299)
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tidal tail
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A long streamer of stars, gas, and dust torn from a galaxy during its close interaction with another passing galaxy. (p. 296)
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velocity dispersion method
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A method of finding a galaxy's mass by observing the range of velocities within the galaxy. (p. 291)
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