Almach (γ And) is one of the finest colour contrast double stars in the sky. To the naked eye it appears as a single bright star of mag. +2.10 but scopes resolve it into an outstanding double consisting of a bright yellow or slightly orange primary and a fainter deep blue secondary. It's widely regarded as the second best colour contrast double in the sky, surpassed only by Albireo (β Cyg) in Cygnus.
Almach is located in the eastern part of Andromeda. It's the the 3rd brightest star in the constellation and is comparable in magnitude to Polaris and the main stars of Ursa Major. To locate Almach the Great Square of Pegasus is a good starting point and in particular its northeastern star Alpheratz (α And). With an apparent magnitude of +2.07, Alpheratz is marginally brighter than Almach. From Alpheratz imagine a line moving in a northeastern direction towards Perseus. The line first passes through delta And (δ And - mag. +3.3) followed by Mirach (β And - mag. +2.1) and then onto Almach.
Any small scope will split Almach. For example, a 80mm (3.1 inch) refractor at 75x will easily transform the star into two colourful Suns separated by 9.4 arc seconds. The colour contrast is stark, the brighter star is a K3 type giant that shines orange yellow while its companion is a hot blue B9 type main-sequence star. Depending on your eyes and seeing conditions you may perceive slightly different colors. It was German physicist and astronomer Johann Tobias Mayer who first identified the star as a double in 1778.
The blue secondary star is actually a triple star and through large amateur scopes on nights of good seeing can be split into components of mag. +5.1 and +6.3. The separation is a measly 0.3 arc seconds and requires apertures of at least 250mm (10-inch) to accomplish. German astronomer Wilhelm Struve in October 1842 discovered it was a double star. In addition, the brighter member of the pair is also a spectroscopic double making this a four star system in total. It's located 358 light-years distant.
Almach is a wonderful double star for all types of telescopes. It's best seen from northern latitudes during the months of October, November and December.
Almach Data Table
|Henry Draper Catalogue (HD)||12533|
|Hipparcos Catalogue (HIP)||9640|
|RA (J2000)||02h 03m 54s|
|DEC (J2000)||42d 19m 47s|
|A/BC Mag.||2.3 / 5.0|
|A/BC Separation (arc secs)||9.4|
|A/BC PA (deg)||63|
|B/C mag.||5.1 / 6.3|
|B/C Separation (arc secs)||0.3|
|B/C PA (deg)||185|
|Other Name Spellings||Almaach, Almaack, Almak, Almaak, Alamak|
|Notable Feature||Four star system. One of the finest colour contrast multiple stars for amateurs.|