Alpha Ursae Majoris


Alpha Ursae Majoris
Alpha Ursae Majoris A/B/C
Ursa major constellation map.png
Stars of Ursa Major, including Dubhe
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 11h 03m 43.7s
Declination +61° 45′ 03″
Apparent magnitude (V) 1.79 (1.87/4.81/7.12)
Characteristics
Spectral type K0 III / F0 V / F8
U−B color index 0.92
B−V color index 1.07
Variable type Pulsating
Astrometry
Radial velocity (Rv) −9 km/s
Proper motion (μ) RA: −136.46 mas/yr
Dec.: −35.25 mas/yr
Parallax (π) 26.38 ± 0.53 mas
Distance 124 ± 2 ly
(37.9 ± 0.8 pc)
Absolute magnitude (MV) −1.09/1.83/4.22
Orbit
Companion α UMa B
Period (P) 44.4 yr
Semimajor axis (a) 0.603"
Eccentricity (e) 0.4
Inclination (i) 152°
Longitude of the node (Ω) 2000°
Periastron epoch (T) 1956.8
Details
Mass 4/1.7 M
Radius 30/1.3 R
Luminosity 300 L
Temperature 4,500/7,400 K
Metallicity ?
Rotation <17 km/s.
Age ? years
Other designations
Dubhe, Dubb, Ak, 50 UMa, HR 4301, BD +62°1161, HD 95689, SAO 15384, FK5 417, GC 15185, ADS 8035, CCDM 11037+6145, HIP 54061.
Database references
SIMBAD data

Alpha Ursae Majoris (α UMa, α Ursae Majoris) is the second-brightest star in the constellation of Ursa Major (despite its Bayer designation of "alpha"). It has the traditional name Dubhe, and a rarer name Ak.

It forms part of the Big Dipper (also known as the Plough or the Great Bear), and is the northern of the 'pointers' (or 'guards'), the two stars of Ursa Major which point towards Polaris, the North Star. Dubhe is about 124 light years away and is typical of a red giant, an evolved helium-burning star. It is also a multiple star, orbited by a main sequence companion, Dubhe B, at a distance of about 23 astronomical units (AU), as well as a close pair, Dubhe C, at a distance of about 8000 AU.

However, it is not part of the Ursa Major Moving Group.

The traditional name comes from the Arabic for "bear", dubb, from the phrase ظهر الدب الاكبر żahr ad-dubb al-akbar "the back of the Greater Bear".

It is known as 北斗一 (the First Star of the Northern Dipper) or 天樞 (the Celestial Pivot) in Chinese.

Dubhe is the official state star of the State of Utah.

Dubhe in Military

USS Dubhe (ID-2562) is once of United States navy ship.


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