| A | B |
|---|
| Binary star | Double-star systems |
| constellation | Groups of stars |
| Nova | a star that suddenly increases in brightness up to 100 tomes in just a few hours or days |
| Nubula | massive cloud of dust and gas between the stars |
| Galaxy | huge collection of stars |
| spiral galaxies | Shaped like a pin- wheel |
| Elliptical galaxies | Shaped like flat disks |
| spectroscope | instrument that braks up light into its characteristic colors |
| spectrum | band of colors formed when light passes through a prism |
| red shift | shift toward the red end of the spectrum of a star that is moving away from the Earth |
| doppler effect | apparent charge in the wavelength of light that occurs when an object is moving toward or away from Earth |
| big-bang theory | theory that states that the universe began to expand with an explosion of concentrated matter and energy and has been expanding ever since |
| gravity | force of attraction between objects |
| quasars | quasi-stellar radio source; distant object that gives off mainly radio waves and X- rays |
| Giant stars | star with a diameter about 10 to 100 tomes as large as the sun |
| supergiant stars | star with a diameter up to 1000 times the diameter of the sun; largest of all stars |
| white dwarfs | small dense star |
| neutron stars | smallest of all stars |
| apparent magnitude | brightness of a star as it appers on the Earth |
| absolute magnitude | amount of light a star actually gives off |
| Hertzsprung- Russell diagram | Chart that shows the relationship between the absolute magnitude and the surface temperature of stars |
| main- sequence stars | in the H-R diagram, a star that lies in an area from the upper left corner to the lower right corner |
| parallax | apparent change in the position of a star in the sky due to the change in the Earth's position as the Earth moves around the sun |
