Alpha Cygni - Deneb

Deneb is the brightest star in the constellation Cygnus, the Swan. A blue-white star of magnitude 1.25, is also the 19th brightest star in the sky. It appears at the northern tip of the Northern Cross, and is one of the vertices of the Summer Triangle (with Altair and Vega).

In Arabic, Deneb's name means "tail" (of the Swan). It has been also known by the traditional names Arided and Aridif, but today these are almost entirely forgotten. Deneb is known as the Fourth Star of the Celestial Ford in Chinese. In the Chinese love story of Qi Xi, Deneb marks the magpie bridge across the Milky Way which allows the separated lovers Niu Lang (Altair) and Zhi Nu (Vega) to be reunited on one special night of the year in late summer.

Due to precession, Deneb was a pole star 18,000 years ago, appearing 7 degrees from the North Celestial Pole. It will be one again around the year 9800 A.D.

Physical Properties

Deneb's exact distance from the Earth is uncertain, but as of 2009, the most likely value is 1425 light years. At that distance, Deneb's luminosity is 54,000 times the Sun's, making it among the most luminous stars known. A star of spectral type A2 Ia, Deneb has a surface temperature of 8,400 K. Based on its temperature and luminosity, and also on direct measurements of its tiny angular diameter (merely 0.002"), Deneb has a diameter 110 times the Sun's. It is one of the largest stars of its kind, and would extend halfway to the orbit of the Earth if placed at the center of our Solar System.

Deneb is also the prototype of a class of variable stars known as Alpha Cygni variables. Its surface undergoes non-radial fluctuations, which cause its brightness and spectral type to change slightly.

Deneb is estimated to contain 15 to 17 solar masses. Its stellar wind causes it to lose mass at the rate of 0.8 millionths of a solar mass per year - 100,000 times the flow rate of the Sun. As a white supergiant, its high mass and temperature mean that the star will have a short lifespan. It has already stopped fusing hydrogen in its core. Just 10 to 12 million years old, Deneb will probably become a supernova within a few million years.

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