Most people think of a constellation as a group of stars when in fact, it is a definite area in the celestial sphere, with internationally agreed boundaries. The areas fit together to make up the sky.
In total, the sky contains 88 constellations. Most of these were named in ancient times. In 150 A.D. the Greek astronomer Ptolemy described 48 patterns, including the well known ones such as Ursa Major (the Great Bear). Babylonian astronomers had recorded many of these before 2000 B.C. Between the 16th and 18th centuries A.D., when explorers ventured into the Southern Hemisphere, new parts of the celestial sphere came into view, and more constellations were added to the ancient ones.
Ursa Minor (the Little Bear) is a constellation of the Northern Hemisphere. A bright star at the tip of of the bearâ€™s tail is the North Star, Polaris. This constellation can be viewed from northern Europe and North America all year round.
The largest constellation is Hydra (the Water Snake), and the smallest one is Crux (the Cross). The faintest space object visible with the naked eye appears dimly in the Andromeda constellation, it is the Andromeda Galaxy, which is 2.2 million light years away.