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