Epsilon Cygni - Gienah

Epsilon Cygni is the third-brightest star in Cygnus, the Swan, at magnitude 2.46. Its traditional name is Gienah, which derives from the Arabic word for wing, "janah". However, Gamma Corvi has an identical traditional name. To differentiate them, γ Crv is referred to as Gienah Ghurab ("Wing of the Raven") or Gienah Corvi; and ε Cyg as Gienah Cygni.

Properties

Gienah (Cygni) is a yellow-orange class K0 III giant star - a common breed among naked-eye stars - with a surface temperature of 4725 K. It shines from a distance of 72 light years, with a luminosity 61 times the Sun's. Its diameter is 12 times solar, and it contains roughly twice the Sun's mass.

Epsilon Cygni is about 1.5 billion years old, and is now beginning its death stages, probably fusing helium in its deep core. Only a few tens of millions of years ago, ε Cyg was a white class A main-sequence star, like Altair. ε Cyg has a fairly high velocity relative to the Sun, speeding along at about 50 km/sec, double the average.

Companion

A very dim, magnitude 11.99 companion lies 78" distant. It is apparently true a companion: while no orbital motion has been seen, the two stars move along through space at the same rate. The companion, a class M3 V red dwarf, is at least 1700 AU away from Gienah and takes at least 50,000 years to make one orbit.

From Gienah, the companion would appear about as bright as Jupiter does in our skies; while from the companion, Gienah would shine twice as brightly as our full Moon. A nearby ninth magnitude star 55" away is merely a line-of-sight coincidence, unrelated to the system.

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