Ursa Major and Ursa Minor
ûr´sə [key] and Ursa Minor [Lat.,=the great bear; the little bear], two conspicuous northern constellations. Known to many peoples from ancient times, these constellations have had various names; the configuration of the seven brightest stars has been called the Bear, Septentriones (the seven plowing oxen), the Plow, Charles's Wain, and the Wagon. Ursa Minor was once known as Cynosura (from the Greek for
dog's tail). In the United States part of Ursa Major is called the Big Dipper (or the Drinking Gourd) and part of Ursa Minor, the Little Dipper. Four of the seven bright stars in the Big Dipper form the bowl and three the handle; five of these stars are of second magnitude. The middle star in the handle of the Big Dipper is Mizar (Zeta Ursae Majoris). A fainter star, Alcor, which appears to be near Mizar, was observed from ancient times. These two stars are sometimes called a double star, but since they do not revolve around a common center of gravity they are not true doubles. Mizar itself is, however, a visual binary star and was the first to be recognized as such—by G. B. Riccioli in 1650. It was also the first spectroscopic binary to be discovered; this observation resulted from studies of the spectrum of the brighter component of Mizar, which revealed it as a binary consisting of a pair of stars of almost equal brightness. The two end stars in the bowl of the Big Dipper are known as the Pointers. A line extending through them to about five times the distance between them leads to the polestar (Polaris, or the North Star). Polaris is at the extreme end of the Little Dipper. Including Polaris there are three stars in the handle of the Little Dipper and four forming the bowl. The handles of the two Dippers extend in opposite directions, and when one bowl is upright the other is inverted. Ursa Major reaches its highest point in the evening sky in April and Ursa Minor its highest point in June. However, for observers in the middle and northern latitudes of the Northern Hemisphere both constellations are circumpolar and thus are visible throughout the year.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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