Eltanin

Gamma Draconis (γ Draconis, abbreviated Gamma Dra, γ Dra), formally named Eltanin , is a star in the northern constellation of Draco. Contrary to its gamma-designation (historically third-ranked), it is the brightest star in Draco at magnitude 2.2, outshining Beta Draconis by nearly half a magnitude and Alpha Draconis by over a magnitude.

Gamma Draconis is at a distance of from the Sun, as determined by parallax measurements from the Hipparcos astrometry satellite. In 1728, while unsuccessfully attempting to measure the parallax of this star, the English astronomer James Bradley discovered the aberration of light resulting from the relative movement of the Earth. Bradley's discovery apparently confirmed Copernicus' theory that the Earth revolved around the Sun.

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. – based on computations from HIPPARCOS data. (The calculations exclude stars whose distance or proper motion is uncertain.) tp://tlgleonid.asuscomm.com/HITACHI/BOOK_ASTRO/S&T/SkyandTelescope_1998%20-%20astronomy/04/199804059063.pdf PDF/ref> 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". From other locations it has a nearby bright, well-known star in Lyra in the night sky; finding Vega, Gamma Draconis is the red star just north-northwest of it.

Properties

Gamma Draconis is an evolved giant star with a stellar classification of K5 III. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It has 72% more mass than the Sun and it has expanded to around 48 times the Sun's girth. It is radiating about 471 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 3,930 K. This is cooler than the Sun, giving this star the orange-hued glow of a K-type star.

Gamma Draconis has six companions listed in double star catalogues. All were discovered by the American astronomer Sherburne Wesley Burnham. The closest may be physically associated and would be separated by about . The luminosity of this object suggests it is a red dwarf star. The others are all much more distant stars unrelated to Gamma Draconis.

Nomenclature

''γ Draconis'' ( Latinised to ''Gamma Draconis'') is the star's Bayer designation.

It bore the traditional name ''Eltanin'' (or ''Etamin'', ''Ettanin'') 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) 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.

Gamma Draconis, along with Beta Draconis, Mu Draconis, Nu Draconis, and Xi Draconis were ''Al ʽAwāïd'' "the Mother Camels", which was later known as the ''Quinque Dromedarii''.

In Chinese, (), meaning '' Celestial Flail'', refers to an asterism consisting of Gamma Draconis, Xi Draconis, Nu Draconis, Beta Draconis and Iota Herculis. Consequently, the Chinese name for Gamma Draconis itself is (, en, the Fourth Star of Celestial Flail.)香港太空館 - 研究資源 - 亮星中英對照表
, Hong Kong Space Museum. Accessed on line November 23, 2010.

Namesake

USS ''Etamin'' was a United States Navy Crater class cargo ship named after the star.

See also

* List of stars in Draco

Notes and references

;References

;Notes

{{DEFAULTSORT:Gamma Draconis
Draconis, Gamma
Draco (constellation)
K-type giants
Eltanin
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Draconis, 33
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Durchmusterung objects