Thanks to James B. Kaler. These contents are the property of the author and are reproduced from original without the author's express consent because of fair use and valid educational purposes.
You take your new telescope to the back yard perhaps wondering what to examine. When finished with the Moon and the bright planets you turn to the stars, first perhaps to the grand Orion Nebula, next maybe to the magnificent Andromeda Galaxy. Then it is time for double stars. The sky abounds with them, northern winter's Castor, springtime's Mizar and Alcor, Summer's Albireo, dozens of others easily found. Among the best of all, however, is the last star of the string of bright beauties that helps make the constellation Andromeda, Almach, Andromeda's Gamma star. The Arabic name, which has nothing to do with its constellation of residence, refers a kind of middle-eastern wild cat. Through the telescope the star is extraordinarily lovely, even a small instrument showing a superb pair separated by a good 10 seconds of arc, the brighter one golden yellow the other blue. Star colors are usually subtle, rather washed out. But put two contrasting stars close together and they play against each other, the colors becoming far more vivid to the eye. Admiral Smythe, who wrote the definitive nineteenth century book on celestial sights, refers to them as "orange and emerald green." The second magnitude brighter component, called "Gamma-1," is a warm class K bright giant with a temperature around 4500 Kelvin and a star now in the act of dying. From its distance of 355 light years, we find a luminosity about 2000 times that of the Sun and a radius 80 solar, big enough to take the star to the orbit of Venus. More remarkable, the fainter blue-green component, Gamma-2, is ALSO double, though the duplicity is far more difficult to see. The two fifth magnitude stars orbit each other with a period of about 60 years, and though they are now near their greatest separation, they are still but a half-second of arc apart, stellar twinkling making them almost impossible to see singly. Yet again the system splits, as the brighter of these two is ALSO double, though detectable only with the spectrograph, the components very close and orbiting every 2.7 days. These three of Gamma-2 are hotter white "main sequence" stars that like the Sun fuse hydrogen to helium, their temperatures in the neighborhood of 10,000 Kelvin. Gamma-2 is thus triple and the naked-eye star we know as Almach quadruple, making it a feast for both the mind and for the eye. One or two other more distant stars might belong to the system as well. (Thanks to Monica Shaw, who helped research this star.)