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Concept
Beta Ursae Minoris
Résumé
Beta Ursae Minoris (β Ursae Minoris, abbreviated β UMi, Beta UMi), formally named Kochab 'koukæb, is the brightest star in the bowl of the Little Dipper asterism (which is part of the constellation of Ursa Minor), and only slightly fainter than Polaris, the northern pole star and brightest star in Ursa Minor. Kochab is 16 degrees from Polaris and has an apparent visual magnitude of 2.08. The distance to this star from the Sun can be deduced from the parallax measurements made during the Hipparcos mission, yielding a value of .
Amateur astronomers can use Kochab as a precise guide for equatorial mount alignment: The celestial north pole is located 38 arcminutes away from Polaris, very close to the line connecting Polaris with Kochab.
β Ursae Minoris (Latinised to Beta Ursae Minoris) is the star's Bayer designation.
It bore the traditional name Kochab, which appeared in the Renaissance and has an uncertain meaning. It may be from الكوكب al-kawkab or כוכב kōkhāv, both of which are broadly used to describe a celestial body and can be translated as 'planet' or 'star'. However, it is more likely derived from Alrucaba or Rucaba, a name applied to Theta Ursae Majoris. In 2016, the International Astronomical Union organized a Working Group on Star Names (IAU-WGSN) to catalog and standardize proper names for stars. The IAU-WGSN's first bulletin, July 2016, included a table of the first two batches of names approved by the IAU-WGSN, which included Kochab for this star.
In Chinese astronomy, 北極 Běi Jí ('North Pole') refers to an asterism consisting of Beta Ursae Minoris, Gamma Ursae Minoris, 5 Ursae Minoris, 4 Ursae Minoris and Σ 1694. Consequently, the Chinese name for Beta Ursae Minoris itself is 北極二 Běi Jí èr ('the Second Star of North Pole'), representing 帝 Dì ('emperor').
This is a 'red' giant star with a stellar classification of K4 III. It is 130 times more luminous than the Sun. Kochab has reached a state in its evolution where the outer envelope has expanded to 42 times the radius of the Sun.
Source officielle
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