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.


At mid second magnitude and just barely the second brightest star in Cassiopeia, almost but not quite as bright as shedir (the Alpha star), Caph, the Beta star, stole its name from the whole "W" of the constellation. The five stars of the "W" splay out like the fingers of a stretched hand, the name "Caph" coming from an Arabic phrase meaning "the stained hand," which refers to an ancient cosmetic coloring by henna. The name eventually went to the Beta star, leaving quite-bright Cih with no name at all. Yet though Gamma is quite marvelous, Caph certainly deserves the honor. In the geometry of the sky, a line through Caph and the more southerly Alpheratz in Andromeda points almost exactly at the Vernal Equinox, the point on the celestial equator where we find the Sun on the first day of spring. Physically, Caph is a class F giant (or subgiant, a not-quite-giant) with a 6700 Kelvin surface, about 900 Kelvin warmer than the Sun. From its very close distance of only 54 light years, Caph is seen to shine with 28 times the brightness of the Sun. It is not unusual in having a small stellar companion, about which little is known, that orbits it every 27 days. Though called a "giant," the star is really not all that large, only about four times as big as the Sun. The term really refers to the state of Caph's evolution, hydrogen fusion in its core having recently stopped. The star is not so much a physical giant but becoming one, the core now contracting, the star cooling and expanding (though no such changes could be seen in a human lifetime). Caph is thus quite unusual in that it is in a particularly rapid state of evolution, and is in a region of temperature and luminosity called the "Hertzsprung Gap" (after the famous Danish astronomer Ejnar Hertzsprung) in which we find few other stars. It will spend only about one percent of its few billion year lifetime in such a condition. With a mass of around double the Sun's, Caph once probably looked much like Summer's Altair. Of these "gap" stars, Caph has a particularly faint "corona," a halo of hot, magnetically heated gas that radiates X- rays (seen around the Sun during a total eclipse). Caph is also unusual in being a "Delta Scuti" type of variable star, in fact the brightest of the breed. Slightly unstable, and rapidly pulsating, a sort of low-mass version of the famed "Cepheid variables," the star varies by about 6 percent in brightness over a 2.5 hour period.