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Second-magnitude Almach, γ Andromedae, is among the best of all double stars in the sky. Its Arabic name, which has nothing to do with its constellation of residence, refers a kind of middle-eastern wild cat.

Meade LX-200 image of Almach (Gamma Andromedae)

Through the telescope, the star is extraordinarily lovely. Even a small instrument shows a superb pair, separated by about 10". The brighter component is golden yellow, and the other blue. Admiral Smythe, who wrote the definitive 19th-century book on celestial sights, refers to them as "orange and emerald green." The magnitude 2.26 A component, called γ1 Andromedae, is a dying class K3 giant with a temperature around 4500 K. From its distance of 355 light years, its luminosity is about 2000 times the Sun's, and its radius is 80 solar radii - large enough to contain the orbit of Venus.

The fainter blue-green component, γ2 Andromedae, is also double, though its duplicity is far more difficult to see. The A-BC pair can be resolved in small telescopes; but the B-C stars are only 0.5" apart, requiring a large aperture to split. Its components are white B8 and A0 main sequence stars of magnitude 5.1 and 6.3, and respective temperatures of about 12,000 and 10,000 K. They orbit each other with a period of 63.7 years, separated on average by only 0.3", which translates to 33 AU. Their eccentric orbit brings them as close as 13 AU and as far apart as 52 AU.

The brighter of these two is also double, though this is detectable only with a spectrograph; its components orbit very closely with a 2.7 day period. The orbit gives a combined mass for the three stars of 8.7 times the Sun's, which is consistent with a lower-mass class A7 dwarf star joined with the advanced B8 and A0 main-sequence components. Hence Almach is in fact a quadruple system. One or two other more distant stars might belong to the system as well.