A constellation is a grouping or configuration of stars perceived as a figure or design. These figures are imaginary and fanciful. In truth, most of the time they don't look anything like what they are named after.
There are other star groupings, such as the Big Dipper, where stars form an obvious pattern, that are called asterisms. Asterisms are usually part of a larger constellation, such as the Big Dipper asterism being part of the constellation of Ursa Major.
Constellations can be a helpful way of finding your way around the sky by the use of signposts such as bright stars and obvious groupings. The human mind has a powerful way of finding patterns and order in seemingly-random chaos. The tradition of grouping stars into constellations goes back thousands of years. Each culture, naturally, had their own groupings and names.
Today, constellations and their boundaries are officially determined by the International Astronomical Union, but the figures of animals, and hunters, and people that make up the constellation are not official. There are 88 official constellations. Some are big and famous, and some are small and obscure.
The grouping of some of the bright stars appearing near to each other in the sky can be obvious, such as Orion, and the Big Dipper. These stars are not necessarily related to each other, and may not even be in the same area of three-dimensional space. They may only seem near to each other from our perspective because they lie on the same line of sight, but may be far apart in space. Other groupings, like the Pleiades, are actually close together in space and are members of the same star cluster.
Back | Up | Next