vendredi 19 septembre 2008

Canis Major 7

Epsilon Canis Majoris (ε CMa / ε Canis Majoris), is the second brightest star in the constellation Canis Major, and one of the brightest stars in the nighttime sky. It has the Bayer designation "epsilon" despite being the second brightest and not the fifth brightest star in its constellation. It also has the traditional name Adhara (sometimes spelled Adara). The name is from the Arabic word عذارى ‘aðāra’, "virgins". It is known as 弧矢七 (the Seventh Star of the Bow and Arrow) in Chinese.
Adhara is a binary star, about 430 light years distant from Earth. The main star possesses an apparent magnitude of +1.5 and belongs to the spectral classification B2. It has a surface temperature of 25,000 K and emits a total radiation equal to 20,000 times that of the Sun. If this star were at the same distance as Sirius, it would appear 15 times brighter than the planet Venus. This star is also one of the brightest known extreme ultraviolet sources in the sky.
The +7.5 magnitude companion star (the absolute magnitude amounts to −5.0) is at 7.5" away with a position angle of 161° of the main star. Despite the relatively large angular distance the components can only be resolved in large telescopes, since the main star is approximately 250 times brighter than its companion.
A few million years ago, Adhara was much closer to the Sun than it is at present, causing it to be a much brighter star in the night sky. About 4,700,000 years ago, Adhara was 34 light years from the Sun, and was the brightest star in the sky with a magnitude of –3.99. No other star has attained this brightness since, nor will any other star attain this brightness for at least five million years.

Delta Canis Majoris (δ CMa / δ Canis Majoris) is a star in the constellation Canis Major. It also has the traditional name Wezen or Wesen. The traditional name comes from the Arabic وزن wazn, meaning a weight. Wazn is also the name for β Columbae.

Beta Canis Majoris (β CMa / β Canis Majoris) is a star in the constellation of Canis Major. It also has the traditional name Murzim, Al-Murzim or Mirzam.
The traditional name is Arabic (مرزم) for 'The Herald', and probably refers to its position, heralding Sirius in the night sky (ie, rising before it). Murzim is a variable magnitude blue-white giant star. The brightness of Murzim varies between 1.95 and +2.00 in a six-hour period. It is a Beta Cephei variable star. It is a star which is currently in the final stages of using hydrogen gas for fuel. It will eventually exhaust its supply and begin using helium for fuel instead.
Beta Canis Majoris is located near the far end of the Local Bubble - a cavity in the local Interstellar medium though which the Sun is traveling.

Eta Canis Majoris (η CMa / η Canis Majoris) is a star in the constellation Canis Major. It also has the traditional name Aludra.
Aludra shines brightly in the skies in spite of a large distance from Earth due to being intrinsically many times brighter (absolute magnitude) than the Sun. A blue supergiant, Aludra has only been around a fraction of the time our Sun has, yet is already in the last stages of its life. It is still expanding and may be becoming a red supergiant, or perhaps has already passed that phase, but in either case it will become a supernova within the next few million years.
The name Aludra originates from the Arabic: عذرا al-‘aðrā "the virgin". In ancient times Arabic astrologers/astronomers referred to a group of four stars in the Canis Major constellation, also known as the "Greater Dog", as Al 'Adhara "the virgins".
η Canis Majoris classified as an Alpha Cygni type variable star and its brightness varies from magnitude +2.38 to +2.48

Zeta Canis Majoris (ζ CMa / ζ Canis Majoris) is a spectroscopic binary in the constellation Canis Major. It also has the traditional name Furud or Phurud, from the arabic فرد al-furud meaning the solitary ones. ζ Canis Majoris is approximately 336 light years from Earth.
The primary component, ζ Canis Majoris A, is a blue-white B-type main sequence dwarf with an apparent magnitude of +3.02. It has an unseen companion, ζ Canis Majoris B. The two stars orbit around their common centre of mass once every 675 days.

Gamma Canis Majoris (γ CMa / γ Canis Majoris) is a star in the constellation Canis Major. It also has the traditional name Muliphein, not to be confused with Muhlifain, which is Gamma Centauri; both names derive from the same Arabic root, محلفين muħlifayn.
γ Canis Majoris is a blue-white B-type bright giant with an apparent magnitude of +4.11. It is approximately 402 light years from Earth.
It is unclear exactly why this relatively faint star was given the "gamma" designation, but it is possibly because it is in the same part of the constellation as Sirius (alpha) and Murzim (beta).

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