The constellation Andromeda is renowned for the Andromeda galaxy, but anyone with even a modest telescope would be remiss to overlook Andromeda’s star Almach (Gamma Andromedae), one of the finest double stars to adorn the sky. Almach, which looks like a single star to the unaided eye, marks the Princess Andromeda’s left foot. Look through the telescope sometime to see Almach transform into two colorful suns.
Star-hop to Almach from the Great Square of Pegasus, the signature star formation of autumn. Two streamers of stars fly outward from the Great Square, starting at the star Alpheratz. Jump three stars over on the lower streamer to locate Almach. At second-magnitude brightness, Almach shines pretty much on a par with the stars of the Big Dipper.
The telescope splits Almach into a larger golden sun and a smaller bluish sun. Practiced telescope users recommend a magnification of 75X or so for the most vivid view of this colorful double. Some double star aficionados believe Almach’s vibrancy of color even surpasses that of Albireo, generally regarded as the sky’s finest double star. In autumn, both Almach and Albireo are there for the viewing, so check them out and decide for yourself.
At 350 light-years, the two stars making up Almach are probably a true binary – two stars revolving around a common center of mass. The smaller blue star is also a hard-to-split telescopic binary.
Almach shines relatively close to the famous variable star Algol. When Algol shines at maximum brilliance, it matches Almach in brilliance.