Alpha Ursae Majoris

Alpha Ursae Majoris A/B

Stars of Ursa Major, including Dubhe
Observation data Epoch J2000      Equinox J2000
Constellation	Ursa Major
Right ascension	11h 03m 43.67152s[1]
Declination	+61° 45′ 03.7249″[1]
Apparent magnitude (V)	1.79[2]
Characteristics
Spectral type	K1 II-III[3] / F0 V[3]
U−B color index	+0.93[2]
B−V color index	+1.07[2]
Variable type	Pulsating
Astrometry
Radial velocity (Rv)	–9[4] km/s
Proper motion (μ)	RA: –134.11[1] mas/yr Dec.: –34.70[1] mas/yr
Parallax (π)	26.54 ± 0.48[1] mas
Distance	123 ± 2 ly (37.7 ± 0.7 pc)
Absolute magnitude (MV)	–1.10 ± 0.04[5]
Orbit[citation needed]
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
α UMa A
Surface gravity (log g)	2.46[6]
Temperature	4,660[6] K
Metallicity [Fe/H]	–0.20 ± 0.07[6] dex
Rotational velocity (v sin i)	2.6 ± 1.0[5] km/s
Other designations
Dubhe, Dubb, Ak, 50 UMa, BD+62 1161, FK5 417, HD 95689, HIP 54061, HR 4301, SAO 15384.[7]
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. 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". In Chinese it is known as 北斗一 (the First Star of the Northern Dipper) or 天樞 (the Celestial Pivot).

This star 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 123 light years away and is a giant star that has evolved away from the main sequence after consuming the hydrogen at its core. It is a spectroscopic binary with a main sequence companion α UMa B that has a stellar classification of F0V. This star orbiting at a mean separation of about 23 astronomical units (AU) and completes an orbit every 44.4 years. More than 90,000 AU distant from this pair is a second binary system that includes an F-type star, making this a four star system.^[8]

Although it is part of the constellation of Ursa Major, it does not form part of the Ursa Major Moving Group of stars that have a common motion through space.^{[citation needed]}

In culture

Dubhe is the official star of the State of Utah. USS Dubhe (ID-2562) was a ship in the United States navy. The Danish National Home Guard Navy ship MHV 806 is named Dubhe.

References