The star Beta Cygni, one of the best-known double stars in the sky. It consists of a K3 bright giant of magnitude 3.1 and a B9.5 dwarf of magnitude 5.1. The stars show contrasting colours of orange and blue-green. The primary is also a close visual binary with a period of just over 200 years. Albireo lies 434 l.y. away.
Subjects: Astronomy and Astrophysics.