| 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 one 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 not 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 sherical or elongated galaxy with a bright center and very little gas or dust. |
| irregular galaxy | a galaxy that does not fit into any other catagory; 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. |
