jeudi 18 septembre 2008

Draco 3

Gamma Draconis

Distance (Light Years)
147.6 ± 3.1
Visual Magnitude
Color (B-V)
Names For This StarThis star is also known as Etamin, Etanin, Ettanin, Rastaban, Rasaben, or the Zenith Star.
The names of this star derive from the Arabic name Al Ras al Tinnin meaning "The Dragon's Head."
The name "Zenith Star" derives from the fact that star moves through the zenith at the latitude of the Royal Observatory in Greenwich, England.
Description of the StarEltanin is a cool, orange K5III giant about 200 times as luminous as the sun. The spectral type implies an effective temperature of about 3800 K, a mass of 5.0 solar masses and a diameter 25 times that of the sun.
Eltanin is a variable star fluctuating by about 0.08 magnitudes in brightness.

Alpha Draconis

Distance (Light Years) 309 ± 15
Visual Magnitude 3.67
Color (B-V) -0.05

Names For This Star

One of the Arab names for the constellation of Draco was Al Thuban, which according to Allen is an Arab translation of "Draco," that is, a dragon. The Arabic name of the constellation has come to be attached to the star.
Another name for the star is Adib from the Arabic Al Dhi'bah, "The Hyenas". A number of stars in Draco, Boötes, and Ursa Major were considered to be among the hyenas.

According to Allen, seamen were accustomed to call Thuban "The Dragon's Tail."

Description of the Star

Thuban is a white A0III giant having a luminosity about 260 times that of the sun. Spectral analysis indicates that Thuban has a companion star orbiting with a 51.4 day period. Burnham gives the separation between the stars as about 20 million miles.

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