EarthSky writes
A constellation is a pattern of stars in the night sky. The word is from the Latin constellacio,meaning a set of stars. There are 88 official constellations, all with well defined boundaries. Many constellations are very old. They are a link between us and our ancestors, a projection of human imagination into the cosmos. Ancient people looked at the stars and thought they saw mythical beings, beasts and cultural touchstones among the stars.
On the other hand, most asterisms are relatively new. Many are small patterns within a constellation, and some are large patterns made of bright stars from multiple constellations. There is nothing official about an asterism, but many are well known. Generally an asterism is a simple pattern that is easy to recognize.
Read more at EarthSky | What’s a constellation? What’s an asterism?
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