Mizar is circled, Alcor is invisible beside it at this scale)
Epoch J2000.0 Equinox J2000.0
|Right ascension||13h 25m 13.53783s|
|Declination||+54° 59′ 16.6548″|
|Apparent magnitude (V)||+3.99|
|Spectral type||A5Vn / M3-4|
|Radial velocity (Rv)||−9.6 km/s|
|Parallax (π)||39.91 ± 0.13 mas|
|Distance||81.7 ± 0.3 ly |
(25.06 ± 0.08 pc)
|Absolute magnitude (MV)||+2.00|
|Surface gravity (log g)||4.25 cgs|
|Rotational velocity (v sin i)||228 km/s|
|Age||0.5 ± 0.1 Gyr|
Alcor // is the fainter companion of Mizar, the two stars forming a naked eye double in the handle of the Big Dipper (or Plough) asterism in the constellation of Ursa Major. The two both lie about 83 light-years away from the Sun, as measured by the Hipparcos astrometry satellite.
Alcor has the Flamsteed designation 80 Ursae Majoris. Alcor was originally Arabic سها Suhā/Sohā, meaning either the ‘forgotten’ or ‘neglected’ one; notable as a faintly perceptible companion of Mizar.
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Alcor for 80 UMa.
Mizar and Alcor's proper motions show they move together, along with most of the other stars of the Big Dipper except Dubhe and Alkaid, as members of the Ursa Major Moving Group, a mostly dispersed group of stars sharing a common birth. However, it has yet to be demonstrated conclusively that they are gravitationally bound. Recent studies indicate that the Alcor binary and Mizar quadruple are somewhat closer together than previously thought: approximately 74,000 ± 39,000 AU or 0.5–1.5 light years. The uncertainty is due to our uncertainty about the exact distances from us. If they are exactly the same distance from us (somewhat unlikely) then the distance between them is only 17800 AU (0.281 ly).
The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.
Al-Sahja was the rhythmical form of the usual Suhā/Sohā. It appears as الخوّار al-Khawwar, 'the Faint One', 
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... the seven rishis in the constellation Saptarishi (Ursa Major) ... In Vasishta (Zeta), its tiny companion star is named after Arundhati, the wife of Vasishta ... today known by their Arabic names Dubhe (Kratu), Merak (Pulaha), Phekda (Pulastya), Megrez (Atri), Benetnash (Marichi) and Mizar (Vasishta) ...
- list of Arabic star names, published in Popular Astronomy, January 1895, by Professor Robert H. West, of the Syrian Protestant College at Beirut.
- "The Celestial Bear, A Micmac Legend". Retrieved 2018-01-01.
- Alcor at Jim Kaler's Stars website
- Alcor (star) on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images