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21 Cards in this Set

  • Front
  • Back
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)