Ursa Major 6

Dubhe
Alpha Ursae Majoris
Distance (Light Years) 123.6 ± 2.5
Visual Magnitude 1.81
Color (B-V) 1.07

Names For This Star

The name Dubhe derives from the Arabic phrase Thahr al Dubb al Akbar meaning "The Back of the Greater Bear".
Description of the Star

Dubhe is an orange K0IIIa giant. The spectral type implies an effective temperature of 4500 K, a mass 4 times that of the sun and 16 times the diameter.
Dubhe's Companion

Megrez
Delta Ursae Majoris
Distance (Light Years) 81.4 ± 1.2
Visual Magnitude 3.32
Color (B-V) 0.08

Names For This Star

Megrez derives from the Arabic term Al Maghrez meaning "The Root of the Tail (of the Bear)."
The The Bright Star Catalog lists Kaffa in Becvar as an alternative designation for Megrez. I have no information about the origin or meaning of this name for the star.

Description of the Star

Megrez is a hot, white A3V main sequence star about 25 times as luminous as the sun. The spectral type implies an effective temperature of 9100 K, a mass of 2.6 solar masses, and a diameter about twice that of the sun.
According to Burnham, Megrez is part of a star cluster including at least 16 other stars from the Ursa Major area of the sky, as well as Mizar, Merak, Alcor, Phecda, and Alioth in the Big Dipper. The Ursa Major cluster represents an ellipsoidal volume of space about 30 ly long by 18 ly in width.



Dubhe has a companion, Dubhe B, separated by 0.672 sec of arc corresponding to a projected distance of 25 AU. The companion appears to be a yellowish F0V main sequence star of about 7400 K temperature, with a mass 1.7 times that of the sun and with 1.3 times the diameter. The Visual Magnitude of the companion is about 4.73.
The combined luminosity of Dubhe and its companion is about 230 times that of the sun.

Dubhe C

There is a third star apparently physically associated with the Dubhe system. Dubhe C is an F8 star of Visual Magnitude 7.12 separated by 280 sec of arc from Dubhe A. This corresponds to a projected distance of about 11,000 AU or 0.17 ly.
The spectrum of Dubhe C indicates that it has itself a near companion that in a 6.4 day orbit.

Merak
Beta Ursae Majoris
Distance (Light Years) 79.4 ± 1.2
Visual Magnitude 2.34
Color (B-V) -0.02

Names For This Star

The name Merak derives from the Arabic name Al Marakk meaning "The Loin", that is, "The Loin of the Bear". "Mirak" is an alternative spelling.
Description of the Star

Merak is a white A1V main sequence star almost 60 times as luminous as the sun. The spectral type implies a mass about three times that of the sun, a diameter more than twice that of the sun, and an effective temperature of 9600 K.
According to Burnham, Merak is part of a star cluster including at least 16 other stars from the Ursa Major area of the sky, as well as Mizar, Alioth, Alcor, Phecda, and Megrez in the Big Dipper. The Ursa Major cluster represents an ellipsoidal volume of space about 30 ly long by 18 ly in width.