Aldebaran (arab. الدَّبَران, litteraly. 'The Follower') (α Tauri, α Tau, Alpha Tauri) is a star and the brightest star in the constellation of Taurus and one of the brightest stars in the nightsky. It has the Bayer designation α Tauri (Alpha Tauri) abbreviated as Alpha Tau or α Tauri.

Aldebaran has an average apparent magnitude of 0.87 (ranging from 0.75 to 0.95) making it (typically) the 14th brightest star in the Night Sky and brightest in its constellation (Taurus). Aldebaran lies circa 65 light-years from Earth. The star lies along the line of sight to the nearby Hyades cluster.

Aldebaran is an orange giant star, meaning its colder than the Sun with a surface temperature of 3900 K, but its 45x the size of the Sun and 400x as lumnious as the Sun. As a giant, it has moved off the main sequence after depleting its supply of hydrogen in the core. It spins slowly and takes 520 days to complete one rotation.

Together with Aldebaran B, located 680 astronomical units away from Aldebaran, it makes a star system. Its companion has an apparent magnitude of 13.21 (80-96 thousand times fainter then Aldebaran)

Name

The name Aldebaran comes from the arabic al Dabaran (الدبران) meaning "the follower" because it seems to follow the Pleiades. In 2016, the International Astronomical Union Working Group on Star Names (WGSN) approoved the name Aldebaran for the star.

Aldebaran is the brightest star in the constellation Taurus, with the Bayer designation α Tauri, Latinised as Alpha Tauri. It has the Flamsteed designation 87 Tauri as the 87th star in the constellation of approximately 7th magnitude or brighter, ordered by right ascension. It also has the Bright Star Catalogue number 1457, the HD number 29139, and the Hipparcos catalogue number 21421, mostly seen in scientific publications.

It is a variable star listed in the General Catalogue of Variable Stars, but it is listed using its Bayer designation and does not have a separate variable star designation.

Aldebaran and several nearby stars are included in double star catalogues such as the Washington Double Star Catalog as WDS 04359+1631 and the Aitken Double Star Catalogue as ADS 3321. It was included with an 11th-magnitude companion as a double star as H IV 66 in the Herschel Catalogue of Double Stars and Σ II 2 in the Struve Double Star Catalog, and together with a 14th-magnitude star as β 550 in the Burnham Double Star Catalogue.

Observation

Aldebaran is one of the easiest stars to find in the night sky, thanks partially to its brightness and partially being nearer to Earth than most other asterisms. Following the three stars of Orion's belt in the direction opposite to Sirius, the first bright star encountered is Aldebaran. It is best seen at midnight between late November and early December.

The star is, by chance, in the line of sight between the Earth and the Hyades, so it has the appearance of being the brightest member of the open cluster, but the cluster that forms the bull's-head-shaped asterism is more than twice as far away, at about 150 light years.