Albireo is a showpiece double star and one of the great small telescope objects. To the naked eye, it's the fifth brightest star in Cygnus (combined mag. +2.9) and the lone star that marks the head of "the Swan" constellation. When viewed through small scopes - or even good 10x50 binoculars - it splits into two components. The primary shines at mag. +3.1 (Albireo A) and the secondary at mag. +5.1 (Albireo B). The stars are separated by a generous 34.3 arc seconds, but what makes this special is the vivid colour contrast between the two components. A brilliant yellow primary, accompanied by a soft blue secondary.
Cygnus represents a Swan flying down the plane of the Milky Way. It contains many bright stars. Positioned at its heart is a prominent asterism in the shape of a large cross, hence the name "Northern Cross". Located at the northern end of the cross is the constellation's brightest star, blue-white supergiant Deneb (α Cyg - mag. +1.3). At the opposite end lies Albireo.
Albireo is easily split with small telescopes at low powers. The surrounding field of view also contains numerous fainter stars, adding to the splendour. At high magnifications, the separation of the two stars is plentiful. Larger scopes improve the colour contrast with many more fainter background stars also visible.
Albireo is located about 430 light-years from the Earth. It's unclear if Albireo A and B are actually a physical binary system. If so, the orbital period would be at least 100,000 years. In 1976, using speckle interferometry it was discovered that Albireo A is a binary star itself. In the Washington Double Star Catalogue, this pair is designated as Aa and Ac with a separation of 0.4 arc seconds. The resolution capability of the average size amateur scope won't split them, but those with extremely large reflectors of the order of 500mm (20-inch) aperture or more may be able to do so under exceptional seeing conditions.
Albireo is a must see object and one of the finest double stars in the night sky. Its beauty comes from the striking colour contrast of the component stars, a brilliant yellow primary and a soft blue secondary. With a wide separation, the double is easily split with small telescopes and even good binoculars. As a result, it's a favourite target for amateur astronomers.
Albireo Data Table
|Components||A (Aa and Ac) and B|
|Angular separation (arc secs)||35.3 (AB), 0.4 (AaAc)|
|Position angle (degrees)||54 (AB)|
|Other Designations||Beta Cygni, β Cyg|
Albireo A Components Data Table
|Name||Albireo Aa||Albireo Ac|
|Washington Double Star Catalogue (WDS)||19307+2758Aa||19307+2758Ac|
|Flamsteed||6 Cygni A||6 Cygni A|
|RA (J2000)||19h 30m 43.286s||19h 30m 43.295s|
|DEC (J2000)||+27d 57m 34.84s||+27d 57m 34.62s|
|Apparent Magnitude Aa and Ac Combined||+3.08||+3.08|
|Other Designations||Beta Cygni A, β Cyg A||Beta Cygni A, β Cyg A|
Albireo B Component Data Table
|Washington Double Star Catalogue (WDS)||19307+2758B|
|Flamsteed||6 Cygni B|
|RA (J2000)||19h 30m 45.395s|
|DEC (J2000)||+27d 57m 55.00s|
|Other Designations||Beta Cygni B, β Cyg B|