| A | B |
|---|
| star | a large celestial body that is composed of gas and that emits light |
| Doppler effect | an observed change in the frequency of a wave when the source or observer is moving |
| light-year | the distance that light travels in one year |
| parallax | an apparent shift in the position of an object when viewed from different locations |
| apparent magnitude | the brightness of a star as seen from the Earth |
| absolute magnitude | the brightness that a star would have at a distance of 32.6 light-years from Earth |
| main sequence | the location on the H-R diagram where most stars lie; it has a diagonal pattern from lower right to upper left |
| nebula | a large cloud of gas & dust in interstellar space; a region in space where stars are born |
| giant | a very large & bright star whose hot core has used most of its hydrogen |
| white dwarf | a small, hot, dim star that is the leftover center of an old star |
| nova | a star that suddenly becomes brighter |
| neutron star | a star that has collapsed under gravity to the point that the electrons & protons have smashed together to form neutrons |
| pulsar | a rapidly spinning neutron star that emits pulses of radio & optical energy |
| black hole | an object so massive & dense that even light cannot escape its gravity |
| constellation | 1 of 88 regions into which the sky has been divided-to describe locations of celestial objects; group of stars in recognizable pattern |
| galaxy | a collection of stars, dust & gas bound together by gravity |
| quasar | quasi-stellar radio source; a very luminous object that produces energy at a high rate |
| cosmology | the study of the origin, properties, processes & evolution of the universe |
| big bang theory | theory that all matter & energy in universe was compressed into an extremely small volume-13 to 15 billion years ago exploded & expanded |
| cosmic background radiation | radiation uniformly detected from every direction in space; considered a remnant of the big bang |
