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Perseus, the ancient hero who rescued Andromeda, climbs the northeastern sky in northern autumn evenings, bright Mirphak marking his side amidst a lovely stream of stars that lie within the autumn Milky Way. Also called "Algenib," Arabic for "side" (a name used for other stars as well), the name Mirphak has nothing to with the hero, and comes from a long Arabic phrase that means "the elbow of the Pleiades." Quite bright, only a bit below first magnitude, Mirphak is the Alpha star of its constellation, just somewhat brighter than its more famed neighbor, the eclipsing double star Algol. Indeed it makes a fine comparison star with which to watch Algol's periodic plunges to third magnitude. Mirphak's rather healthy distance of 600 light years implies great brilliance, the star a mid-temperature (7000 Kelvin) class F supergiant with a luminosity 5400 times that of the Sun and a radius 60 times solar. The star is important in that it lies just at the edge of the properties of the class of stars known as Cepheid variables, pulsating stars whose periods are linked to their luminosities, allowing them to be precise cosmic yardsticks with which to measure the distances of galaxies. Mirphak is thus instrumental in defining the natures of such stars, and may be a very modest pulsator itself. Unlike most constellations, many of the stars of Perseus are physically associated, resulting in the figure's great prominence. Mirphak is the brightest star of the young "Alpha Persei Cluster," which contains many of the fainter surrounding stars, most of which quite hot and massive, the "elbow of the Pleiades" having something of a "Pleiades" of its own. The cluster is one of a handful easily visible to the naked eye, and is a spectacular sight in a small telescope.