At magnitude 2.42, Beta Pegasi is the second-brightest star in the constellation Pegasus, lying at the northwest corner of the Great Square asterism. Its traditional name is Scheat, from Arabic, meaning "the shin" or "the foreleg". The name has nothing to do with the horse Pegasus, having been misplaced from another constellation; confusingly, this name is also sometimes used for Delta Aquarii.
Properties
Scheat is unusual among bright stars in having a relatively cool surface temperature (3700 K); its color quite noticeable, especially through binoculars or a telescope. Scheat is a class M2.5 II-III red giant. From its distance of 200 light years, the star is 340 times more luminous than the Sun visually. However, Scheat radiates most of its light in the infrared, and when that is taken into account, its true luminosity climbs to 1500 times the Sun's. To produce this much energy, the star must be 95 times the Sun's radius. Scheat is big enough and close enough that its angular diameter (0.015") is easily measured, which gives the same physical size.
Like many red giants of its class, Scheat is an irregular variable star. Its brightness varies from magnitude +2.31 to +2.74, a range 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 stellar wind, in which water vapor has been found.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]