Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Tau Cygni is a binary star system in the constellation Cygnus, approximately 69 light years away from Earth. The main star, 4th magnitude GJ 822.1 A, is a yellowish white subgiant star of the spectral type F2IV. It therefore has a surface temperature of 6,000 to 7,500 kelvins and is larger, hotter, and several times as bright as our Sun. Its companion, 6th magnitude GJ 822.1 B, is a yellow main sequence star of the spectral type G0V. It is similar to our Sun in size, surface temperature, and luminosity.