| A | B |
|---|
| 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 |
