ALKAID (Eta Ursae Majoris). Though the name may not be so well known, the star certainly is, as Alkaid is the end star in the handle of the Big Dipper, the great asterism that makes most of the grand constellation Ursa Major, the Greater Bear. Just fainter than Dubhe, the front bowl star of the Dipper, second magnitude (1.85) Alkaid is the third brightest star in the constellation and places number 35 in the list of the brightest stars. Though Johannes Bayer generally listed stars by Greek letter names in order of brightness within a constellation, the stars of the Dipper are named from west to east, rendering Alkaid Eta Ursae Majoris rather than Beta. Different cultures see the sky differently as well. Alkaid's Arabic name means "the leader," and appears to refer to the "daughters" (the handle of the Dipper) that stand by a funeral bier made of the Dipper's bowl. Alkaid is also known as Benetnasch, which also refers to the daughters. Alkaid is almost exactly 100 light years away. With a surface temperature of about 20,000 degrees Kelvin, is one of the hotter stars that can be seen with the naked eye, and therefore glows to us a soft blue-white. Like the Sun, it is a "main-sequence" star that shines by fusing hydrogen into helium in its core. However its mass of six times that of the Sun renders it both hotter and over 700 times more luminous. Were Alkaid our Sun, we would have to be 25 times farther away to survive, almost to the orbit of Neptune. It one of the two renegades of the Dipper. The five middle stars are all moving through space together as part of a loosely bound cluster. Alkaid and Dubhe, however, are moving in their own directions, ultimately dooming the Dipper's shape. The star is just below the temperature limit at which stars produce strong X-rays as a result of shock waves in their winds, and is therefore only a weak source of X-rays.
Written by Jim Kaler. Return to STARS.