ENIF (Epsilon Pegasi). Though given only the fifth letter of the Greek alphabet by Bayer, Enif, at mid second magnitude (2.39), is still the brightest star in the constellation Pegasus. It just beats out Markab (Alpha) and Scheat (Beta), both in the Great Square, which received Alpha through Delta, showing the Square's importance. Enif is the brightest by cheating a bit, as it is rather roundly trounced by Alpheratz, Delta Pegasi. Modern constellation boundaries, however, place Alpheratz formally in Andromeda, where it is better known as Alpha Andromedae, leaving the field clear for Enif to triumph. The name, from Arabic, means "the nose," referring to the muzzle of Perseus' winged horse, with which he rescued Andromeda. Physically, Enif is a coolish, orange class K (K2) supergiant with a temperature of 4460 Kelvin. From its distance of 670 light years, we calculate a total luminosity 6700 times that of the Sun, as befits a supergiant. Also befitting its great status is its diameter, which from direct measures of angular diameter and its luminosity and temperature is 150 times that of the Sun, large enough to take the star halfway to the orbit of the planet Venus. If Enif were our star, 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 dying and massive. It seems to have a mass around 10 times that of the Sun and is now either fusing its helium into carbon and oxygen or is about to start. Like Betelgeuse, it might either explode as a supernova or turn into a heavy, rare neon-oxygen white dwarf that has shrunk to less than the size of Earth. Even with all these great qualities, however, Enif still seems like an ordinary (if such there be) supergiant. Two characteristics set it apart. It seems to be part of a family of three very similar supergiants, the other two the Alpha and Beta stars of nearby Aquarius, Sadalmelik and Sadalsuud. The triplets, all at roughly the same luminosity and distance (Sadalmelik at 760 light years, Sadalsuud at 610) may have been born together in the same extended group, and over the past 15 or so million years of their existence have drifted well over 100 light years apart. Most intriguing, however, is Enif's possible erratic and violent behavior. In 1972, an observer in Florida saw Enif as bright as Altair in Aquila, five times brighter than normal, whereupon it faded. For over 10 minutes it appeared to pop some kind of enormous flare, one vastly brighter than the small ones that occur frequently on the Sun. Such events are rare -- only two dozen or so are known -- and not well documented, nor is there any theory for them. We apparently do not understand supergiants -- or any other kind of star for that matter -- quite as well as we think we do. (Thanks to Jason Pero, who helped research this star.)
Written by Jim Kaler. Return to STARS.