At magnitude 2.39, Epsilon Pegasi is the brightest star in Pegasus. Its traditional name Enif, from Arabic, means "the nose," referring to the "muzzle" of the winged horse Pegasus.
Properties and Evolution
Physically, Enif is a cool, orange class K2 Ib supergiant with a temperature of 4460 K. From its distance of 670 light years, it has a total luminosity of 6700 suns. From direct measures of angular diameter, as well as luminosity and temperature, it is 150 times the size of the Sun. If Enif were at the center of our solar system, it would appear 40° across in our sky - about the angular extent of the entire constellation of Pegasus itself!
As a supergiant, Enif is both massive and dying. It contains around 10 solar masses, and is fusing its core helium into carbon and oxygen (or is about to start doing so). Enif likely only has a few million years left to live, although it is unknown whether the star will explode as a supernova, or die as a rare neon-oxygen white dwarf; its mass straddles the dividing line.
Enif seems to be part of a family of three very similar supergiants; the other two are the α and β stars of nearby Aquarius (Sadalmelik and Sadalsuud). The triplets, all at roughly the same luminosity and distance, may have been born together in the same extended group, and have drifted over 100 light years apart during the past 15 or so million years.
Most intriguing, however, is Enif's possible erratic and violent behavior. Enif has been observed to brighten radically upon a few occasions, giving rise to the theory that it (and possibly other supergiants) erupt in massive flares that dwarf the Sun's. In 1972, an observer in Florida reported Enif to be as bright as Altair - five times brighter than normal - for over 10 minutes, after which it faded. Such events are rare - only two dozen or so are known - and not well documented, nor is there any theory for them.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]