Gamma Draconis (γ Draconis, abbreviated Gamma Dra, γ Dra), formally named Eltanin/ɛlˈteɪnɪn/,[9][10] is a star in the northern constellation of Draco. Contrary to its gamma-designation (historically third-ranked), it is the brightest object in Draco at magnitude 2.2,[1] outshining Beta Draconis by nearly half a magnitude and Alpha Draconis by over a magnitude.
In 1.5 million years, Gamma Draconis will pass within 28 light-years of Earth. For a period, if its current absolute magnitude does not change, it will be the brightest star in the night sky, nearly as bright as Sirius is at present.[13][14] It is by far the brightest star having a zenith above a point near London which led to its vaunting in these places as the "zenith star".[15] Nearby this red star to the south-southeast is Vega, a bright, well-known star in Lyra.
Properties
Gamma Draconis is an evolvedgiant star with a stellar classification of K5 III.[3] Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[16] It has about two times more mass than the Sun[4] and it has expanded to around 50 times its size. It is radiating about 600 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 3,964 K.[7] This is cooler than the Sun, giving this star the orange-hued glow of a K-type star.[17]
Gamma Draconis has six companions listed in double star catalogues. All were discovered by the American astronomer Sherburne Wesley Burnham.[18] The closest may be physically associated and would be separated by about 1,000 AU. The luminosity of this object suggests it is a red dwarf star.[19] The others are all much more distant stars unrelated to Gamma Draconis.[20]
It bore the traditional name Eltanin[13][21] derived from the Arabic التنين At-Tinnin 'The great serpent'. The name Rastaban was formerly used for Gamma Draconis, and the two terms share an Arabic root meaning "serpent" or "dragon". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[22] to catalogue and standardize proper names for stars. The WGSN approved the name Eltanin for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[10]
In Chinese, 天棓 (Tiān Bàng), meaning Celestial Flail, refers to an asterism consisting of Gamma Draconis, Xi Draconis, Nu Draconis, Beta Draconis and Iota Herculis.[23] Consequently, the Chinese name for Gamma Draconis itself is 天棓四 (Tiān Bàng sì, English: the Fourth Star of Celestial Flail.)[24]
Namesake
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^ abcHatzes, A. P.; Endl, M.; Cochran, W. D.; MacQueen, P. J.; Han, I.; Lee, B.-C.; Kim, K.-M.; Mkrtichian, D.; Döllinger, M.; Hartmann, M.; Karjalainen, M.; Dreizler, S. (2018-02-16), "The Radial Velocity Variability of the K-giant γ Draconis: Stellar Variability Masquerading as a Planet", The Astronomical Journal, 155 (3): 120, arXiv:1801.05239, Bibcode:2018AJ....155..120H, doi:10.3847/1538-3881/aaa8e1, ISSN0004-6256
^Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
^Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN978-1-931559-44-7.
^Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; et al. (July 1997), "The Hipparcos Catalogue", Astronomy and Astrophysics, 323: L49 –L52, Bibcode:1997A&A...323L..49P
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