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GIENAH GHURAB
Gienah (je-nuh), an obscure name for an important star in a prominent but small constellation, Corvus, the Crow or Raven, a very noticeable skewed box that crosses the sky just to the west of first magnitude Spica in Virgo. The name is from an Arabic phrase that means "the Raven's Wing." Gienah is the right-hand star at the top of the box and one of the "pointers" to Spica (the other Algorab), as if Spica really needs such. Though the brightest star in the constellation, just over the second magnitude line to third, Bayer oddly gave it the Gamma designation, Alpha a fourth magnitude star beneath the right-hand side of the prominent box. Gienah is a class B blue giant with a temperature of 12,400, not much greaster than that of the much brighter supergiant Rigel in Orion. From its distance of 165 light years, it shines 355 times more brightly than the Sun, from which we find a diameter four times solar, the blue giants nowhere near as large as their much cooler red counterparts. Though an evolved giant, the star, about four times as massive as the Sun, is still close to the "main sequence," and is either in the very last stages of core hydrogen fusion or the fusion has stopped altogether, the helium core now in a state of contraction. Over the next few million years, Gienah will become a red giant. Gienah's odd chemical composition separates it from the more ordinary "blue giants," the star a member of the class of "mercury- manganese" stars, the brightest of which is Alpheratz in Andromeda. The mercury-manganese stars have hugely elevated levels of these and other elements, mercury up to 100,000 times normal, while having depletions of others, such as aluminum and nickel. These chemical peculiarities are the result of the physical separation of different kinds of atoms in the stellar atmosphere, some sinking down through gravity, others lofted up by radiation. Gienah was only fairly recently discovered to be such a star because its rather rapid rotation speed of 150 kilometers per second obscures its spectrum.