GIENAH CYGNI (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, 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 4725 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 relativeto 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.