In astronomy, an asterism is a pattern of stars recognized in the Earth's night sky. It may be part of an official constellation or it may be composed of stars from more than one constellation.

Colloquial usage does not draw a sharp distinction between "constellation" in the sense of an asterism (pattern of stars) and "constellation" in the sense of an area of the sky surrounding an asterism. The modern system of constellations used in astronomy employs the latter concept. For example, the asterism known as the Big Dipper comprises the seven brightest stars in the IAU constellation that is called Ursa Major.