Front

A cluster of stars, stellar remnants, dust, gas, and often planetary systems.

Back

galaxy

Front

Earth's planetary system

Back

solar system

Front

Planets gravitationally bound in orbit around stars.

Back

Planetary system

Front

Hypothetical substance made of subatomic particles, 24% of the universe, affects galaxies.

Back

dark matter

Front

Solid, rocky natural satellites orbiting planets.

Back

Moon

Front

A large spherical object in stable orbit around a star, made of liquid, solids, or gas.

Back

planet

Front

Extraterrestrial object of frozen gas, rock, and dust orbiting a star; heat causes coma and tail.

Back

comet

Front

Distance light travels in a year; equals 9.46x10^12 km or nearly 6 trillion miles.

Back

Light Year

Front

Low energy left over in the universe after the Big Bang

Back

Cosmic Background Radiation (CBR)

Front

Infinitely small and dense spot where the universe began

Back

The Singularity