A constellation is akin to an asterism, but it is usually much more complicated, containing more stars or larger areas of the sky. A few asterisms are constellations: the asterism called the Southern Cross, for example, is the constellation Crux (the Cross). Modern constellations are mostly named after mythological themes, such as gods, legendary heroes, creatures, or structures. Although most constellations resemble the figures after which they are named, others are not as recognizable.

The constellations encompass the entire celestial sphere and provide a visual reference frame. Astronomers can plot the stars and other objects in the universe using constellations, charting the apparent movement that is caused by Earth’s own rotation and orbit.