Gamma Draconis

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Gamma Draconis
Template:Location mark
Location of γ Draconis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 2.23[2]
Characteristics
Spectral type K5 III[3]
U−B Template:Engvar +1.87[2]
B−V Template:Engvar +1.52[4]
Astrometry
Radial velocity (Rv)Script error: No such module "val".[5] km/s
Proper motion (μ) RA: −8.48[1] mas/yr
Dec.: −22.79[1] mas/yr
Parallax (π)21.14±0.10 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)−1.93 ± 0.07[6]
Details[4]
MassScript error: No such module "val". Template:Solar mass
RadiusScript error: No such module "val".[7] Template:Solar radius
LuminosityScript error: No such module "val".[7] Template:Solar luminosity
Surface gravity (log g)Script error: No such module "val".[8] cgs
TemperatureScript error: No such module "val".[7] K
Metallicity [Fe/H]Script error: No such module "val". dex
Rotational velocity (v sin i)Script error: No such module "val". km/s
AgeScript error: No such module "val". Gyr
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist
Database references
SIMBADdata

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Gamma Draconis, formally named Eltanin Template:IPAc-en,[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.

Gamma Draconis is at a distance of Script error: No such module "convert". from the Sun,[1] as determined by parallax measurements from the Hipparcos astrometry satellite.[11][12] In 1728, while unsuccessfully attempting to measure the star's parallax, James Bradley discovered the aberration of light resulting from the relative movement of the Earth. Bradley's discovery confirmed Copernicus' theory that the Earth revolved around the Sun.[13] It is drifting closer to the Solar System with a radial velocity of about –28 km/s.

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] Nearby this red star to the south-southeast is Vega, a bright, well-known star in Lyra.

Nomenclature

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

It bore the traditional name Eltanin[13] (historically also seen with other spellings like Etamin) 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".[15] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[16] 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 traditional Arabic astronomy, 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.[15]

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Celestial Flail, refers to an asterism consisting of Gamma Draconis, Xi Draconis, Nu Draconis, Beta Draconis and Iota Herculis.[17] Consequently, the Chinese name for Gamma Draconis itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx.)[18]

Observational history

Gamma Draconis lies near the zenith of Greenwich, London, and so has been known as the "zenith star" in that region.[15] This made it an object of interest for 17th- and 18th-century English astronomers, including Robert Hooke, to attempt to measure its parallax.[19] In 1728, while unsuccessfully attempting to measure the star's parallax, James Bradley discovered the aberration of light resulting from the relative movement of the Earth. Bradley's discovery was thought to confirm Copernicus' theory that the Earth revolved around the Sun.[13] Due to its historical significance, George Airy in 1873 called it "the birth-star of modern astronomy".[20]

Properties

Gamma Draconis is an evolved giant 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.[21] 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.[22]

Gamma Draconis has six companions listed in double star catalogues. All were discovered by the American astronomer Sherburne Wesley Burnham.[23] The closest may be physically associated and would be separated by about Script error: No such module "val".. The luminosity of this object suggests it is a red dwarf star.[24] The others are all much more distant stars unrelated to Gamma Draconis.[25]

The star displays periodic radial velocity variations that had been suspected to be caused by an orbiting planet, but later turned out to be caused by intrinsic stellar variability.[4] Similar variability may exist in other giant stars, such as 42 Draconis and Aldebaran, resulting in false positive planet detections.[26][27]

In culture

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

Ursula K. Le Guin's novel Planet of Exile is set on the third planet orbiting Gamma Draconis.[28]

See also

Notes and references

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  1. ↑ a b c d e f g Script error: No such module "Citation/CS1".
  2. ↑ a b Script error: No such module "Citation/CS1".
  3. ↑ a b Script error: No such module "citation/CS1".
  4. ↑ a b c d Script error: No such module "citation/CS1".
  5. ↑ Script error: No such module "citation/CS1".
  6. ↑ Script error: No such module "citation/CS1".
  7. ↑ a b c d Script error: No such module "Citation/CS1".
  8. ↑ Script error: No such module "citation/CS1". Gamma Draconis' database entry at VizieR.
  9. ↑ Script error: No such module "citation/CS1".
  10. ↑ a b Script error: No such module "citation/CS1".
  11. ↑ Script error: No such module "citation/CS1".
  12. ↑ Script error: No such module "citation/CS1".
  13. ↑ a b c d Script error: No such module "citation/CS1".
  14. ↑ Script error: No such module "Citation/CS1". – based on computations from HIPPARCOS data. (The calculations exclude stars whose distance or proper motion is uncertain.)
  15. ↑ a b c Script error: No such module "citation/CS1". Also available online here
  16. ↑ Script error: No such module "citation/CS1".
  17. ↑ Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.
  18. ↑ Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.
  19. ↑ Script error: No such module "Citation/CS1".
  20. ↑ Script error: No such module "citation/CS1".
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ Script error: No such module "citation/CS1".
  23. ↑ Script error: No such module "Citation/CS1".
  24. ↑ Script error: No such module "citation/CS1".
  25. ↑ Template:Cite DR2
  26. ↑ Script error: No such module "Citation/CS1".
  27. ↑ Script error: No such module "Citation/CS1".
  28. ↑ Script error: No such module "citation/CS1".

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Template:Sky Template:Stars of Draco

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