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.