Albireo (Beta Cygni) is the fifth brightest star in the constellation Cygnus. Albireo appears to be a third magnitude single star when viewed with the naked eye. However, it offers one of the most beautiful contrasting double stars when viewed through almost any scope, consisting of Albireo A (amber, apparent magnitude 3.1), and Albireo B (blueish, apparent magnitude 5.1), separated by 35 seconds of arc.

The Albireo system is about 380 light years away. The brighter components of Albireo A are a stable helium-fusing giant of class K3, and a hydrogen-fusing main-sequence star of class B9. The K3 giant has a temperature of around 4400 K, a luminosity 950 times the Sun's, a radius 50 times solar, and a mass of about 5 times solar. Its close companion comes in at 11,000 K, 100 solar luminosities, and 3.2 solar masses.

Albireo B is similar to Albireo A's companion. It is a class B8 main-sequence star with a temperature of 12,100 K, a luminosity of 190 suns, and a mass of 3.3 suns. It is a very rapid rotator, with an equatorial velocity of at least 250 km/sec, and a rotation period less than 0.6 days. As is often the case among such fast-spinning stars, Albireo B is a "B-emission star" that is surrounded by a gas disk of its own making. From Albireo B, Albireo A would appear as brilliant orange and blue points about half a degree apart, the K giant shining with the light of 35 full Moons, and its class B companion at about half of that.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]