the epsilon, or fifth brightest, star in the constellation Ursa Major. Also called the Great Bear, Ursa Major is a circumpolar group of stars in the Northern Hemisphere that is visible throughout the year and moves counter-clockwise around the north celestial pole. The 32nd brightest of all known stars and one of the 57 stars of celestial navigation, Alioth is positioned at the tail of the Bear.
Alioth is one of about 20 stars in the Ursa Major constellation that move together through space in a cluster. Dubhe, the star that had been designated the alpha, or brightest, star in the Ursa Major constellation, is not a member of this streaming cluster. Both Alioth and Dubhe belong to the distinct set of stars that form the Big Dipper, but due to an irregularity in the naming convention, Alioth—designated the fifth brightest in the constellation—is in fact the brightest of the seven stars that comprise the Big Dipper. Alioth is the third star from the end of the Dipper’s handle. It reaches its highest point in the sky on May 21, when the handle appears to be standing on end. In October and November, the seven stars of the Dipper are close to the horizon, and seeing them is a little more difficult than usual.
The stars of the Big Dipper have long and rich mythological histories. The meaning of the name Alioth is not altogether clear but may derive from the Arabic Alyat, which means the “fat tail” of an animal. Alternatively, the name may derive from the Arabic phrase Al Haur, which means the “white of the eye,” or the phrase Al Hawar, which means the “bright eye.” The Chinese called this star Yu Kang in reference to an ancient astronomical instrument. In Hindu lore, the seven stars of the Big Dipper represented the seven sages, and Alioth represented the sage named Angiras.
Alioth is a blue-white star with an apparent magnitude of +1.79; it is 85 times more luminous than the sun and is located about 70 light-years from Earth. Its variable periods of radial velocity may be due to some unseen companion stars. Together with these companions, the Alioth system has a radial velocity—the actual velocity with which a star moves along the observer’s line of sight—of roughly 5.5 miles (8.9 kilometers) per second in approach.