Alkaid
Easternmost star of the Big Dipper, a blue-white B-type main sequence star.
Alkaid, also designated Eta Ursae Majoris, is a star in the constellation Ursa Major. It is the easternmost star in the Big Dipper (or Plough) asterism and, with an apparent visual magnitude of +1.86, is the third-brightest star in the constellation and one of the brightest stars in the night sky. Unlike most stars of the Big Dipper, it is not a member of the Ursa Major moving group.
Quick Facts
- Bayer designation
- Eta Ursae Majoris
- Apparent visual magnitude
- +1.86
- Stellar classification
- B3 V
- Age
- roughly six million years
- Equatorial radius
- 2.89 solar radii
- Polar radius
- 2.66 solar radii
Facts from the source article.
Lore & Background
Alkaid is a B-type main sequence star with a stellar classification of B3 V. Since 1943, its spectrum has served as one of the stable anchor points by which other stars are classified. It is a young star, roughly six million years old, and is in the beginning of its life on the main sequence. The star rotates rapidly, with a projected rotational velocity that, corrected for its inclination angle, implies an equatorial rotational velocity. As a consequence of its rapid rotation, Alkaid is oblate, with a radius of 2.89 solar radii at the equator and 2.66 solar radii at the poles. The effective temperature varies across latitudes, being 16,300 K at the equator and 17,700 K at the poles, giving it the blue-white hue of a B-type star. It is an X-ray emitter. The star has broadened absorption lines due to its rapid rotation, which is common in stars of this type, though the lines are very slightly distorted and variable, possibly caused by some emission from a weak disk of material produced by the rapid rotation. No exoplanets or companion stars have been discovered.
Reader's Guide
Alkaid bears the traditional name derived from an Arabic phrase meaning 'The leader of the daughters of the bier.' In this context, the daughters of the bier—the mourning maidens—are the three stars of the handle of the Big Dipper: Alkaid, Mizar, and Alioth, while the four stars of the bowl (Megrez, Phecda, Merak, and Dubhe) represent the bier itself. In Chinese astronomy, it is known as Běidǒuqī (the Seventh Star of the Northern Dipper) or Yáoguāng (the Star of Twinkling Brilliance). Hindus viewed this star as Marīci, one of the seven Saptarshis. In Japan and Korea, Alkaid is known as Hagunsei and Mukokseong respectively, both meanings deriving from ancient Chinese influence. The star has been used in culture: the USS Alkaid (AK-114) was a United States Navy Crater class cargo ship named after the star; Alkaid is one of the Behenian fixed stars used in alchemy; and the fossil starfish Alkaidia is named after Alkaid.
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