| A | B |
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| constellation | an apparent group of stars originally named for mythical characters; the sky is presently divided into 88 constellations |
| binary star | one of two stars revolving around a common center of mass under their mutual influence |
| light-year | the distance light travels in a year, about 9.5 trillion kilometers |
| main-sequence star | a star that fallis into the main sequence category on the H-R Diagram, this category contains the majority of stars |
| red giant | a large, cool star of high luminosity; a star occupying the upper-right portion of the H-R diagram |
| nova | a star that explosively increases in brightness |
| protostar | a collapsing cloud of gas and dust destined to become a star |
| supernova | an exploding star that increases in brightness many thousands of times |
| white dwarf | a star that has exhausted most or all of its nuclear fuel and has collapsed into a very small size, believed to be near the final stage of evolution |
| neutron star | a star of extremely high density composed entirely of neutrons |
| pulsar | a variable radio source of small size that emits radio pulses in very regular periods |
| black hole | a massive star that has collapsed to such a small volume that its gravity prevents escape of everythig, including light |
| galaxy | a group of stars, dust and gases held together by gravity |
| big bang theory | the theory that proposes that the universe originated as a single mass, which subsequently exploded |
| Hubble's Law | a law that states that the galaxies are retreating from the Milky Way at a speed that is proportional to their distance |
