| A | B |
|---|
| absolute magnitude | brightness of a star as it would appear if located 32.6 light-years from the earth |
| apparent magnitude | brightness of a star as it appears from the earth |
| barred spiral galaxy | type of spiral galaxy with a bar of stars that runs through its center |
| binary star | pair of stars that revolve around each other |
| black hole | a dead star with gravity so great that not even light can escape, formed by the collapse of a very large supernova |
| circumpolar | describing any star that is always visible in the night sky and, from the Northern Hemisphere, can be seen circling Polaris |
| constellation | pattern of stars |
| elliptical galaxy | type of galaxy with a very bright center that contains little dust and gas and is spherical to disklike in shape |
| galaxy | large-scale group of stars |
| giant | very large, cool, bright star |
| globular cluster | spherically shaped group of hundreds of stars located around the core of the Milky Way Galaxy |
| H-R diagram | Hertzsprung-Russell diagram; graph showing the relationship of the surface temperature and absolute magnitude of a star |
| irregular galaxy | type of galaxy with no identifiable shape and an uneven distribution of stars within it |
| light-year | distance that light travels in one year, about 9.5 trillion km |
| main-sequence star | star with characteristics that place it within a band running through the middle of the H-R diagram |
| nebula | dark cloud of gas and dust in space; first stage in the development of a star |
| neutron star | collapsed core of a supernova consisting of a small, extremely dense ball of neutrons |
| nova | white dward star that explodes as it cools, temporarily becoming thousands of times brighter |
| open cluster | loosely shaped group of hundreds of stars |
| parallax | method of determining the distance from the earth to a star based on the shift in the apparent position of the star when viewed from different angles |
| planetary nebula | expanding shell of gases shed by a dying star |
| protostar | inside a nebula, the shrinking, spinningcenter region; the second stage in the development of a star |
| pulsar | neutron star that emits two beams of radiation that sweep across space |
| quasar | starlike object that gives off radio waves and X rays |
| red shift | apparent lengthening of the light waves emitted by a star moving away from the earth |
| spiral galaxy | type of galaxy with a nucleus of bright stars and flattened arms that swirl around the nucleus |
| star | body of gases that gives off a tremendous amount of radiant energy in the form of light and heat |
| supergiant | extremely large, giant star |
| supernova | star that blows apart with a tremendous explosion |
| white dwarf | small, hot, dim star |
