mardi 23 septembre 2008

Ursa Minor 6


Gamma Ursae Minoris (γ UMi / γ Ursae Minoris) is a slightly variable star in the constellation Ursa Minor. It also has the common name Pherkad. Together with Beta Ursae Minoris, Gamma forms the end of the dipper pan of the "Little Dipper". The name "Pherkad" derives from the Arabic for "the two calves," which originally referred to both Kochab and Pherkad. Together, they are also called the "Guardians of the Pole."
Gamma Ursae Minoris has apparent magnitude +3.00. It is approximately 480 light years from Earth and is of spectral class A3, meaning it has a surface temperature of 7,500 to 11,000 kelvins. It is classified as a Delta Scuti type variable star and its brightness varies by 0.05 magnitudes with a period of 3.43 hours. It is 1100 times more luminous than the Sun, and possesses a radius 15 times that of the Sun.
Pherkad
Al-Farqad
The calf
فرقد


Epsilon Ursae Minoris (ε UMi / ε Ursae Minoris) is a triple star system in the constellation Ursa Minor. It is approximately 347 light years from Earth. Epsilon Ursae Minoris also carries the seldom used proper name Urodelus, Greek for "Conspicuous Tail" of the Bear or Dog.
The primary component, Epsilon Ursae Minoris A, is an eclipsing spectroscopic binary. It is classified as a yellow G-type giant with a mean apparent magnitude of +4.21. In addition to light changes due to eclipses, the system is also classified as an RS Canum Venaticorum type variable star and its brightness varies from magnitude +4.19 to +4.23 with a period of 39.48 days, which is also the orbital period of the binary. The binary it orbited by a third component, Epsilon Ursae Minoris B, which is an 11th magnitude star, 77 arcseconds away on the sky.


Zeta Ursae Minoris (ζ UMi / ζ Ursae Minoris) is a star in the constellation Ursa Minor. It also has the traditional name Alifa al Farkadain.
Zeta Ursae Minoris is a white A-type main sequence dwarf with an apparent magnitude of +4.32. It is approximately 376 light years from Earth.
Despite its classification as a dwarf star, Zeta UMi is 3.4 times the mass of the sun and its luminosity is about 200 solar luminosities. At a surface temperature of 8700 kelvins, this star is actually on the verge of becoming a giant star. Zeta UMi may also be a variable of the delta scuti type.


Delta Ursae Minoris (δ UMi / δ Ursae Minoris) is a star in the constellation Ursa Minor. It also has the traditional name Yildun, Vildiur, or Gildun, as well as Pherkard.
Delta Ursae Minoris is a white A-type main sequence dwarf with an apparent magnitude of +4.35. It is approximately 183 light years from Earth.


Eta Ursae Minoris (η UMi / η Ursae Minoris) is a star in the constellation Ursa Minor. It also has the traditional names Anwar al Farkadain and Alasco.
Eta Ursae Minoris is a yellow-white F-type main sequence dwarf with an apparent magnitude of +4.95, making it visible to the naked eye. It is approximately 97.3 light years from Earth.

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