| A | B |
|---|
| spectrum | the rainbow of colors produced when white light passes through a prism or spectrograph |
| apparent magnitude | how bright a light appears to an observer |
| absolute magnitude | the actual brightness of a star |
| light-year | a unit of length equal to the distance that light travels through space in 1 year |
| parallax | an apparent shift in the position of an object when viewed from different locations |
| H-R diagram | Hertzsprung-Russell diagram; a graph that shows the relationship between a star's surface temperature and its absolute magnitude |
| main sequence | a diagonal pattern of stars on the H-R diagram |
| white dwarf | a small, hot star near the end of its life; the leftover center of an old star |
| red giant | a star that expands and cools once it runs out of hydrogen fuel |
| supernova | the death of a large star by explosion |
| neutron star | a star in which all the particles have become neutrons; the collapsed remains of a supernova |
| pulsar | a spinning neutron star that emits rapid pulses of light |
| black hole | an object with more than three solar masses squeezed into a ball only 10 km across whose gravity is so strong that now even light can escape |
| galaxy | a large grouping of stars in space |
| spiral galaxy | a galaxy with a bulge in the center and very distinctive spiral arms |
| elliptical galaxy | a spherical or elongated galaxy with a bright venter and very little dust and gas |
| irregular galaxy | a galaxy that does not fit into any other category; one with an irregular shape |
| nebula | a large cloud of dust and gas in interstellar space; the location of star formation |
| open cluster | a group of stars that are usually located along the spiral disk of a galaxy |
| globular cluster | a group of older stars that looks like a ball of stars |
| quasar | "quasi-stellar" object; a star-like source of light that is extremely far away; one of the most powerful sources of energy in the universe |
| cosmology | the study of the origin and future of the universe |
| big bang theory | the theory that states the universe began with a tremendous explosion |
| cosmic background radiation | radiation left over from the big bang that fills all of space |
| spectrograph | an instrument used to spread starlight out into its colors |
| OBAFGKM | star classification by temperature differences |
| Polaris | the North Star, directly above the Earth's north pole |
