| A | B |
|---|
| Local Group | Group of 45 galaxies including the Milky Way |
| nebula | cloud of gas and dust in space |
| spectroscope | instrument used to look at spectra of elements |
| absolute magnitude | measure of the amount of light that a star actually gives off |
| apparent magnitude | measure of teh amount of light from a star that is recieved on Earth |
| magnitude | brightness of a star |
| parallax | a measure of the apparent shift of a star against a background field over 6 months, used to determine distance to stars |
| Milky Way | our spiral galaxy containing approximately 200 billion stars |
| quasar | galaxy that is just forming and is emitting a lot of energy |
| black hole | an object so dense that nothing can escape its gravity field, formed from a collapsed neutron star more than 3x the mass of the sun |
| galaxy | large group of stars, gas, and dust held together by gravity |
| background radiation | left-over microwave energy from the Big Bang |
| gravity | force of attraction between two objects, dependent on their masses and the distance between them |
| blue shift | indicates that an object is moving towards you |
| red shift | indicates that an object is moving away from you |
| emission spectrum | given off by heated elements, shows bright lines |
| wavelength | distance between the crest of one wave to the crest of the next wave |
| absorption spectrum | given off by stars, shows an almost continuous spectrum with missing (dark) lines |
| supernova | massive explosion created by giant stars when they become unstable--forms the heavy elements |
| light-year | distance light traves in a year--9.5 trillion kilometers, standard unit of measure in space |
