What is a constellation?
A constellation is a group of stars that forms a recognizable pattern in the night sky. Astronomers now use the term for 88 official regions of the sky, each containing a traditional star pattern.
People in many cultures grouped stars into patterns representing animals, heroes and objects, and told stories about them. Many of the constellations used today come from ancient Greek astronomy, recorded by Ptolemy around AD 150, which was itself influenced by Babylonian astronomy. Examples include Orion, Leo, Cassiopeia and Ursa Major.
The stars in a constellation usually are not close to each other in space. They only appear near each other from Earth's point of view. One star might be 50 light-years away, while another in the same pattern is 1,000 light-years away.
Constellations and asterisms
Some famous star patterns, like the Big Dipper and Orion's Belt, are not official constellations but asterisms, smaller patterns within or across constellations. Sailors and travelers have used constellations for navigation for thousands of years, and they still help people find their way around the sky.
Did You Know?
The 12 constellations that the Sun appears to pass through during the year are known as the zodiac constellations.