Theta Herculis

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Theta Herculis
Hercules Historical View.png
Historical view of the Hercules constellation showing Rukbalgethi Genubi (θ Her) as the "southern knee"
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 17h 56m 15.1805s[1]
Declination 37° 15′ 01.941″[1]
Apparent magnitude (V) 3.851[1][2]
Spectral type K1IIaCN[1]
U−B color index +1.40 [3]
B−V color index +1.35[3]
R−I color index +0.63[4]
Variable type Irregular[5]
Radial velocity (Rv) –28.32[1] km/s
Proper motion (μ) RA: 2.74[1] mas/yr
Dec.: 7.24[1] mas/yr
Parallax (π) 4.87 ± 0.54[6] mas
Distance approx. 670 ly
(approx. 210 pc)
Absolute magnitude (MV) −2.71+0.26
Mass 6.5[8] M
Radius ~80[8] R
Luminosity 2,400[8] L
Surface gravity (log g) 1.28[7] cgs
Temperature 4,330[2][8] K
Metallicity [Fe/H] −0.24[2] dex
Rotational velocity (v sin i) 3.4 ± 0.6[7] km/s
Age 550-780[8] Myr
Other designations
Rukbalgethi Genubi, θ Her, 91 Her, BD +37° 2982, FK5 672, GC 24415, HD 163770, HIP 87808, HR 6695, SAO 66485
Database references

Theta Herculis (θ Her, θ Herculis) is a fourth-magnitude star in the constellation Hercules. It has the traditional name Rukbalgethi Genubi.


Theta Her is a variable K-type giant star with stellar classification K1IIaCN. In 1935, French astronomer P. Muller identified Theta Herculis as an irregular variable with a range of magnitudes between 3.7 and 4.1 and a periodicity of roughly 8–9 days.[5]


In the Calendarium of Al Achsasi Al Mouakket, this star was designated Rekbet al Jathih al Aisr, which was translated into Latin as Genu Sinistrum Ingeniculi, meaning the left knee of the kneeling man.[9] The traditional name Rukbalgethi Genubi that is encountered in various texts is etymologically similar to the stars Ruchbah and Zubenelgenubi, the term "ruchbah" meaning "knee" while "genubi" signifies "southern"—hence the "southern knee", a meaning which can be gleaned more easily by looking at the accompanying constellation map.[10]

In Chinese, 天紀 (Tiān Jì), meaning Celestial Discipline, refers to an asterism consisting of θ Herculis, ξ Coronae Borealis, ζ Herculis, ε Herculis, 59 Herculis, 61 Herculis, 68 Herculis and HD 160054.[11] Consequently, θ Herculis itself is known as 天紀九 (Tiān Jì jiǔ, English: the Ninth Star of Celestial Discipline.)[12]

See also[edit]


  1. ^ a b c d e f g "SIMBAD query result: tet Her -- Variable Star". Centre de Données astronomiques de Strasbourg. Retrieved 2010-07-26. 
  2. ^ a b c McWilliam, Andrew (December 1990). "High-resolution spectroscopic survey of 671 GK giants". Astrophysical Journal Supplement Series. STI 74: 1075–1128. Bibcode:1990ApJS...74.1075M. doi:10.1086/191527. ISSN 0067-0049. 
  3. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV data. SIMBAD. Bibcode:1986EgUBV........0M. 
  4. ^ "Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR. Centre de Données astronomiques de Strasbourg. Retrieved 2010-07-27. 
  5. ^ a b Muller, P. (January 1935). "Sur la variabilité de θ Herculis". Journal des Observateurs (in French). ADS 18: 177. Bibcode:1935JO.....18..177M. 
  6. ^ Perryman, M. A. C.; et al. (1997), "The Hipparcos Catalogue", Astronomy & Astrophysics 323: L49–L52, Bibcode:1997A&A...323L..49P 
  7. ^ a b c Carney, Bruce W.; et al. (March 2008), "Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars", The Astronomical Journal 135 (3): 892–906, arXiv:0711.4984, Bibcode:2008AJ....135..892C, doi:10.1088/0004-6256/135/3/892 
  8. ^ a b c d e Kaler, James B. "THETA HER (Theta Herculis)". Stars. University of Illinois. Retrieved 2010-07-27. 
  9. ^ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society 55: 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429. 
  10. ^ Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14. 
  11. ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  12. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 26 日

External links[edit]

Coordinates: Sky map 17h 56m 15.20s, +37° 15′ 02.0″