Components of the Universe

Front

star

Back

a giant ball of hot gas, made mostly of hydrogen and helium

Front

light-year

Back

the distance that light travels in one year, about 9.46 trillion kilometers

Front

luminosity

Back

the amount of energy a star gives off from its surface (brightness)

Front

Hertzsprung-Russell (HR) diagram

Back

a graph plotting star luminosity and temperature

Front

galaxy

Back

huge group of stars, dust, gas, planets, and other objects bound together by gravity

Front

spiral galaxy

Back

galaxy that appears to have a bulge in the center and arms that spiral outward in a pinwheel pattern

Front

elliptical galaxy

Back

galaxy shaped like a round or flattened ball

Front

irregular galaxy

Back

galaxy that does not have a regular shape

Front

universe

Back

all of space and everything in it

Front

Big Bang theory

Back

a theory that proposes that the universe formed in an instant in an enormous explosion