distance light can travel in a vacuum in one year; equal to approximately 9.5 X 1012 km

a classification of all forms of radiation by wavelength and frequency; used to study components of the universe

a tool for observing spectral lines

a measure of how bright a star really is, if all stars were the same distance from Earth

a measure of how bright a star appears as seen from Earth

the number of times a wave passes a certain point in a given amount of time

a system of stars and associated matter, held together by gravitational attraction

a diagram that shows the relationship between the brightness, surface temperature, and color of stars

total amount of light (energy) emitted by a star or other celestial body

clouds of dust and gas; site of star formation; remains of dead or dying stars

different colors of light emitted based on the chemical composition of the light source

all of space and its contents

a scientific theory concerning the early development and shape of the universe from a dense state which began and is still expanding