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Eta Ursae Majoris
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 13h 47m 32.4s
Declination +49° 18′ 48″
Apparent magnitude (V) 1.85
Characteristics
Spectral type B3 V
U-B color index -0.67
B-V color index -0.19
Variable type ?
Astrometry
Radial velocity (Rv) -11 km/s
Proper motion (μ) RA: -121.23 mas/yr
Dec.: -15.56 mas/yr
Parallax (π) 32.39 ± 0.74 mas
Distance 101 ± 2 ly
(30.9 ± 0.7 pc)
Absolute magnitude (MV) -0.60
Details
Mass 6 M
Radius 1.8 R
Luminosity 700 L
Temperature 22,000 K
Metallicity ?
Rotation ~200 km/s
Age ? years
Other designations
Alkaid, Benetnash, Benetnasch, Elkeid, 85 Ursae Majoris, HR 5191, BD +50°2027, HD 120315, SAO 44752, FK5 509, GC 18643, HIP 67301.
Book plate by Sydney Hall depicting Ursa Major's stars

Eta Ursae Majoris (η UMa / η Ursae Majoris) is a star in the constellation Ursa Major. It has the traditional names Alkaid (or Elkeid) and Benetnash (Benetnasch).

It is known as 北斗七 (the Seventh Star of the Northern Dipper) or 搖光 (the Star of Twinkling Brilliance) in Chinese.

Alkaid is the most eastern (leftmost) star in the Big Dipper (Plough) asterism. However, unlike most stars of the Big Dipper it is not a member of the Ursa Major moving group.

Alkaid has apparent magnitude +1.9, making it the 35th brightest star in the sky. It is a young bluish-white main sequence star of spectral class B3 V. At 20,000 kelvins it is one of the hotter stars visible with the naked eye.

The name derives from "The leader of the daughters of the bier". The daughters of the bier; i.e., the mourning maidens, are the three stars of the handle of the Big Dipper, Alkaid, Mizar (star), and Alioth.

External links

  • Alkaid at Jim Kaler's Stars website
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