By John Lindell – Updated March 24, 2022
In astronomy, an asterism is a recognizable pattern formed by a group of stars. While each asterism belongs to a larger constellation, many are celebrated on their own.
The Big Dipper (or Ursa Major’s dipper) is an iconic asterism within the northern constellation Ursa Major. Its seven bright stars—Dubhe, Merak, Phecda, Megrez, Alioth, Mizar, and Alkaid—form the familiar “bowl” and “handle.” Mizar, the second star in the handle, is a well‑known double star visible to the naked eye, with its companion Alcor just 20 seconds of arc away.
Orion’s Belt is a trio of stars—Alnitak, Alnilam, and Mintaka—situated in the center of the hunter Orion. The linear arrangement of these stars is a handy celestial compass: following a straight line to the right leads to Sirius, the brightest star in the night sky, located in the constellation Canis Major.
The Big Dipper remains visible throughout most of the northern hemisphere’s night sky, making it a reliable reference for stargazers. Orion, on the other hand, is best observed during autumn and winter evenings in the United States.
Both asterisms offer additional points of interest. In Orion, the “dagger” of the Orion Nebula (M42) hangs just below the belt’s middle star, Alnilam. In the Big Dipper’s handle, the Mizar–Alcor pair provides a classic demonstration of double‑star observation.
