| A | B |
|---|
| main sequence | A star that is at the point in its life cycle in which it is actively fusing hydrogen nuclei into helium nuclei; also, the band of the Hertzsprung-Russel diagram depicting such stars |
| giant star | A large star with great luminosity and a diameter 10 to 100 times greater than that of the sun |
| supergiants | The most luminous, most massive stars, with diameters greater than 100 times the diameter of the sun |
| white dwarfs | The remnant of a giant star that has lost its outer atmosphere; the glowing stellar core |
| nebula | A large cloud of gas and dust in space |
| planetary nebula | A halo of gases that is formed by the expelled layers of a star's atmoshere |
| supernova | The brilliant burst of light that follows the collapse of the iron core of a massive star |
| neutron star | The superdence remains of a massive star that collapsed with enough force to push all of its electrons into the nuclei they orbit, resulting in a mass of neutrons |
| pulsar | A distant neutron star that emits rapid pulses of light and radiowaves instead of steady radiation |
| black hole | The final life stage of an extremley massive star, with a gravt. field so intense that light can not escape |
| galaxies | A group of millions, or even billions stars held together by gravity |
| quasar | A very distant, extr. lumi. celst. obj. that scientists consider to be a type of active galactic nuclei |
| big bang model | Thetheory holding that the universe originated from the instant expansion of an extremly small agglomeration of matter of extremly high density and temperature |
| electromagnetic radiation | energy radiated in the form of a wave, resulting from the motion of electric charges and the magnetic fields they produce |
| electromagnetic spectrum | A continuum depicting the range of electromagnetic radiation, with the longest wavelength at one end and the shortest end at the other |
| continuous spectrum | A spectrum that contains all colors and wavelengths |
| emmision spectrum | A spectrum consisting of individual lines at characterisic wavelengths produced when light passes through an incandescent gas, a bright-line spectrum |
| absorption spectrum | A continuous spectrum crossed by dark lines produced when light passes through a nonincandescent gas |
| constellation | A group of stars that appear to form a pattern in the sky |
| apparent magnitude | The measure of how bright a star appears to be from an observer on Earth |
| astronomical unit | The average distance between the Earth and the Sun, which is about 150million kilometers |
| light year | The distance that light travels in one year, about 9.5trillion kilometers |
| parsec | A unit of measurement used to describe distances between celestial objects, equal to 3.258 light-years |
| luminosity | The brightness of a star |
| absolute magnitude | The measure of how bright a star would be if it were located 10 parsecs from Earth |
| cepheid variable | A variable that brightens and dims regularly, or pulses, and whose distance can be determined from its period of pulsation |
