31 Cygni

31 Cygni, also known as ο¹ Cygni, Omicron¹ Cygni, or V695 Cygni, is a star in the constellation Cygnus.

The Bayer letter ο has been variously applied to two or three of the stars 30, 31, and 32 Cygni. 31 Cygni has been designated as either ο¹ or ο² Cygni. For clarity, it is preferred to use the Flamsteed designation 31 Cygni rather than one of the Bayer designations.

It is an Algol-type eclipsing binary and ranges between magnitudes 3.73 and 3.89 over a period of ten years. The component stars are an orange supergiant of spectrial type K4Iab and a blue-white star likely to be evolving off the main sequence with a spectral type of B4IV-V.

ο² Cygni is about a degree away to the north, also a detached eclipsing binary system containing a cool giant and a small hot star. 30 Cygni is another naked eye star a tenth of a degree away from the 31 Cygni pair, forming a bright triple.