Alpha Persei - Mirfak

At magnitude 1.82, Alpha Persei is the brightest star in Perseus, just outshining the constellation's best known star Algol. Mirfak is circumpolar when viewed from the latitude of New York or higher. It also bears the traditional names of Mirfak and Algenib. Mirfak (also spelled Mirphak, Marfak or Mirzac) comes from a long Arabic phrase "Mirfaq al-Thurayya" that means "the elbow of the Pleiades." Algenib (also spelled also spelled Algeneb, Elgenab, Genib, Chenib or Alchemb) is derived from "al-janib", Arabic for "side"; it is a name also used for γ Peg.

In traditional Chinese astronomy, α Per forms part of Tien Yuen, the Heavenly Enclosure. In Native Hawaiian astronomy, the star is named Hinali'i, and is meant to commemorate a great tsunami, and mark the beginning of the migration of Maui. According to some Hawaiian folklore, Hinali'i is the point of separation between the earth and the sky that happened during the creation of the Milky Way.

Properties and Evolution

Mirfak's measured distance of 590 light years implies great brilliance. The star is a yellow-white class F5 Ib supergiant, with a surface temperature of 6180 K, a luminosity of 5000 suns, and a radius 62 times solar. The luminosity and temperature imply that the star contains about 7 - 8 solar masses.

Only 30 to 50 million years ago Mirfak was a hot blue star of class B. It currently has a dead helium core, or may have begun fusing helium into carbon and oxygen. Currently, α Per lies just at the warm edge of the class of stars known as Cepheid variables, the pulsating stars whose periods are linked to their luminosities, allowing them to be precise cosmic yardsticks with which to measure the distances of galaxies. Mirfak is instrumental in defining the natures of such stars, and may be a very modest pulsator itself.

Many of the stars in Perseus are physically associated, resulting in the figure's great prominence. Mirfak is the brightest member of the young α Per Cluster, or Melotte 20, which is easily visible in binoculars, and contains many of the fainter surrounding stars, most likely including δ Per. The cluster is one of a handful easily visible to the naked eye, and is a spectacular sight in a small telescope. The cluster's distance as a whole is 575 light years, consistent with Mirfak's individual distance. The cluster's age of 50 million years fits as well.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]