γ Andromedae


Gamma Andromedae, Almach, is one of the finest binary systems in the heavens, a triple system (Struve 205ABC) best seen in small telescopes. The primary and components BC form a lovely colour contrast of yellow and blue: 2.3, 5.0; PA 63º and separation 9.4".

The companion C orbits B every 61.1 years. These two stars (5.3, 6.5) are currently only about 0.2" apart at PA 96º according to the latest observations. (Note, as often happens, observations do not always match the ideal orbit; compare the data given here with the calculated orbit: gamma.)

Gamma Andromedae is easiest found with the naked eye as the third of the four stars which wrap themselves around Cassiopeia. From alpha Andromedae move northeast to beta, then an equal distance and you are at gamma.

With gamma on the upper edge of your view, you'll find the fine star cluster, NGC 752 just out of view to the south, a slight move to the south will bring this cluster into view.

Just out of view, to the west, is the interesting star upsilon Andromedae, which was the first discovered ‘solar system’ with three planets. Later a fourth was added.
     The planets orbit at distances of 0.06 AU, 0.83 AU, 2.5 AU, and 5.2 AU. An AU (‘astronomical unit’) is the distance of the Earth to the Sun; thus the second planet with an orbiting distance of .83 AU is similar to the earth's. The orbital periods are 4.6 days, 241 days, 1276.5 days, and 3848.8 days. The masses of the four are .62 Jupiter masses, 1.8, 3.75, and 0.96.
     As for the ‘sun’ of this system--upsilon Andromedae--it's about the same size as our Sun and is 44 light years away.

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