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Albereo, Beta Cygni, 6 Cygnus

The constellation of Cygnus the Swan flies southwestwards along the band of the Milky Way during northern summers. Bright Deneb marks the tail of the Swan, while at the opposite end of the prominent cross-shaped star group the Swan's beak is represented by the star Albireo. As well as forming the beak of the Swan, Albireo is also the base of the formation known as the Northern Cross. It lies at the southern edge of Cygnus, at the point where that constellation meets Vulpecula.

Albireo is distinctive double star with contrasting components. Albireo A is the brighter of these two components, with a magnitude of +3.1 and a golden-orange colour due to its K-type stellar spectrum. Albireo B is rather less bright in the skies of Earth, and is a B-type dwarf star with a distinctly blue colouration. Both of these stars are about 430 light years from the Solar System, though it is not certainly known whether they form a very wide binary system, or are simply unrelated stars positioned closely together in space.

What is known is that Albireo A has a smaller and fainter companion star in a much closer orbit. Thus potentially Albireo is a ternary or triple system, with Albireo A and its close companion being distantly orbited by blue Albireo B over periods measured in hundreds of millennia.


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