Magnitude 2.79 Apparent magnitude (V) 2.79 | ||
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Similar Gamma Draconis, Thuban, Iota Draconis, Zeta Draconis, Sigma Draconis | ||
Beta Draconis (β Draconis, abbreviated Beta Dra, β Dra), also named Rastaban, is a binary star and the third-brightest star in the northern circumpolar constellation of Draco. With an apparent visual magnitude of 2.79, it is bright enough to be easily seen with the naked eye. Based upon parallax measurements from the Hipparcos astrometry satellite, it lies at a distance of about 380 light-years (120 parsecs) from the Sun.
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Nomenclature
β Draconis (Latinised to Beta Draconis) is the system's Bayer designation. It also bears a double star designation of ADS 10611.
It bore the traditional name Rastaban, which has also been used for Gamma Draconis. This name, less commonly written Rastaben, derives from the Arabic phrase ra's ath-thu'ban "head of the serpent/dragon". It was also known as Asuia and Alwaid, the latter meaning "who is to be destroyed," though some trace it to Arabic al'awwad "the lute player". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Rastaban for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.
Beta Draconis is part of the asterism of the Mother Camels (Arabic al'awa'id), along with Gamma Draconis (Eltanin), Mu Draconis (Erakis), Nu Draconis (Kuma) and Xi Draconis (Grumium), which was later known as the Quinque Dromedarii.
In Chinese, 天棓 (Tiān Bàng), meaning Celestial Flail, refers to an asterism consisting of Beta Draconis, Xi Draconis, Nu Draconis, Gamma Draconis and Iota Herculis. Consequently, Beta Draconis itself is known as 天棓三 (Tiān Bàng sān, English: the Third Star of Celestial Flail.)
Properties
The binary system consists of a supergiant orbited by a dwarf companion once every four millennia or so.
Compared to the Sun, this is an enormous star with six times the mass and roughly 40 times the radius. At this size, Beta Draconis is emitting about 950 times the luminosity of the Sun from its outer envelope at an effective temperature of 5,160 K, giving it the yellow hue of a G-type star. The spectrum matches a stellar classification of G2 Ib–IIa, with the luminosity class notation Ib–IIa indicating it lies part way between the bright giant and giant stages of its stellar evolution. It is about 67 million years old.