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Alkaid in the Big Dipper of Ursa Major. |
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| 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 |
| 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 |
| Rotation | ~200 km/s |
| Other designations | |
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).
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 Arabic phrase meaning "The leader of the daughters of the bier" (قائد بنات نعش qā'id bināt naʿsh). The daughters of the bier, i.e. 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, are the bier.
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It is known as 北斗七 (the Seventh Star of the Northern Dipper) or 搖光 (the Star of Twinkling Brilliance) in Chinese
In Japan, Alkaid in known as Hagunsei ("the military breaking star" or "most corner star"). Both meanings come from ancient China's influence in Japan. In Chinese fortune-telling, north is believe to be very unlucky direction. Northwest is even worse. Hunters and soldiers traditionally did not point guns and weapons in the direction of Hagunsei[1]
USS Alkaid (AK-114) was a United States Navy Crater class cargo ship named after the star.