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GIENAH

(Epsilon Cygni). Proper star names can be confusing, as many are so similar. Think for example of Deneb in Cygnus, Denebola in Leo, Deneb Kaitos in Cetus, Deneb Algedi in Capricornus, the word "Deneb" meaning tail and referring to the tails of the animals represented by the constellations. "Gienah" is the pinnacle of confusion, as the same word is used for stars in two constellations. Meaning "wing" in Arabic, Gienah represents a wing of Corvus the Crow (Gamma Corvi) and the eastern outstretched wing of Cygnus the Swan (Epsilon Cygni). To differentiate them, the star in Corvus will be referred to as Gienah Corvi or Gienah Ghurab, that in Cygnus as Gienah Cygni, where the ending on the constellation name implies possession in Latin ("Cygni" and "Corvi" meaning "of Cygnus" and "of Corvus"). Bayer rather obviously lettered the stars of Cygnus more by placement than brightness. While first magnitude Deneb, the brightest, received its deserved "Alpha," fifth-ranked Albireo got "Beta." Gienah stands third, following third-ranked Sadr, which lies at constellation-center. Gienah (Cygni) is a second magnitude (2.46, almost third) yellow- orange class K (K0) giant star, a common breed among naked-eye stars. It shines to us from a distance of 72 light years with a luminosity 61 times that of the Sun from a surface heated to 4800 degrees Kelvin, its diameter 12 times solar. With a mass roughly twice double the Sun's, it is about 1.5 billion years old. Now beginning to die, and probably fusing helium in its deep core, the star was a white class A ordinary dwarf only a few tens of millions of years ago, perhaps one like Altair. It is a bit unusual in that it has a fairly high velocity relative to the Sun, speeding along at about 50 kilometers per second, double the average. Gienah also has a rather odd companionship. A nearby ninth magnitude star 55 seconds of arc away is a mere line-of-sight coincidence, while an apparently true very dim thirteenth magnitude companion lies 78 seconds of arc distant. While no orbital motion has ever been seen, the two stars move along through space at the same rate. The companion, a class M red dwarf, is at least 1700 Astronomical Units away from Gienah (40 times Pluto's distance from the Sun) and takes at least 50,000 years to make one orbital circuit. From Gienah, the companion would appear about as bright as Jupiter does in our skies, while from the companion, Gienah would shine with a luminosity of over 2 full Moons.