Thanks to James B. Kaler. These contents are the property of the author and are reproduced from original without the author's express consent because of fair use and valid educational purposes.

SCHEAT

Scheat (she-at), at the northwest corner of the famed Great Square of Pegasus , rises first to announce the coming appearance of the constellation of the "Winged Horse," which in mythology Perseus rode to rescue Andromeda. From Arabic meaning "the shin," the name has nothing to do with the horse, having been misplaced from another constellation, though it is sometimes translated as "the foreleg." At the fainter end of second magnitude and the Beta star of Pegasus, variable Scheat averages the second brightest star in the Great Square. Unusual for a modestly bright star, Scheat has a fairly low surface temperature of about 3700 degrees Kelvin, 65% that of the Sun, and is categorized as a "class M" red giant or even supergiant, its color quite noticeable, especially through binoculars or the telescope. From its distance of 200 light years, we calculate the star to be 340 times more luminous to the eye than the Sun. However, Scheat radiates most of its light in the invisible infrared, and when that is taken into account, the true luminosity climbs to 1500 times the solar energy output. To produce this much radiation at that temperature requires the star to be 95 times the solar radius. Consistent with its giant status, the star, if placed at the Sun, would extend 70% of the way to the orbit of Venus. Scheat is big enough and close enough that its angular diameter of 0.015 seconds of arc (6-millionths of a degree) is easily measured, from which we derive the same physical size. Like many red giants of its class, Scheat is actually an irregular variable star that slowly changes from middle second magnitude to bright third, a range of half a magnitude that is easily visible to the naked eye. There is no particular period of variation, and the star's changes are unpredictable. Scheat is surrounded by a thin envelope of gas, produced by its strong wind, in which water vapor has been found.