Tau Herculis

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Tau Herculis
Hercules Historical View.png
Historical view of the Hercules constellation showing Rukbalgethi Shemali (τ Her) as the "northern knee"
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 16h 19m 44.4368s[1]
Declination 46° 18′ 48.119″[1]
Apparent magnitude (V) 3.89[1]
Spectral type B5 IV[1]
U−B color index -0.57[2]
B−V color index -0.155[2]
Radial velocity (Rv) -13.8[1] km/s
Proper motion (μ) RA: -13.15[1] mas/yr
Dec.: 39.31[1] mas/yr
Parallax (π) 10.37 ± 0.53[3] mas
Distance 310 ± 20 ly
(96 ± 5 pc)
Absolute magnitude (MV) -1.03
Mass 4.9[4] M
Radius 3.55 ± 0.19[5] R
Luminosity 700[4] L
Surface gravity (log g) 4.02 ± 0.05[5] cgs
Temperature 15,615 ± 301[5] K
Metallicity [Fe/H] 0.15[6] dex
Rotational velocity (v sin i) 46[7] km/s
Age 1[4] Gyr
Other designations
Rukbalgethi Shemali, τ Her, 22 Her, HR 6092, BD 46° 2169, HD 147394, FK5 608, HIP 79992, SAO 46028, GC 21987, CCDM J16197+4619A
Database references

Coordinates: Sky map 16h 19m 44.437s, +46° 18′ 48.12″

Tau Herculis (τ Her, τ Herculis) is a fourth-magnitude star in the constellation Hercules. Its traditional name Rukbalgethi Shemali, though seldom used today in scientific journals, means the "northern knee". It is a blue subgiant star, seven hundred times more luminous than the Sun.


Tau Herculis is a blue subgiant star with stellar classification B5IV. Its mass is 4.9 times solar.[4] Though its apparent magnitude is only 3.89, like all B-class stars, it is very luminous boasting a total bolometric luminosity that is 700 times solar.[4] Hipparcos estimated its distance at roughly 96 parsecs from Earth, or 310 ± 20 light years away.


Its traditional name Rukbalgethi Shemali is of Arabic origin and shares certain etymological characteristics with the stars Ruchbah and Zubeneschamali signifying Hercules' "northern knee".[8] The star was the north pole star around the year 7400 BC, a phenomenon which is expected to reoccur in the year 18,400 due to precession.[4]

In Chinese, 七公 (Qī Gōng), meaning Seven Excellencies, refers to an asterism consisting of τ Herculis, 42 Herculis, φ Herculis, χ Herculis, ν1 Boötis, μ1 Boötis and δ Boötis.[9] Consequently, τ Herculis itself is known as 七公二 (Qī Gōng èr, English: the Second Star of Seven Excellencies.)[10]

See also[edit]


  1. ^ a b c d e f g SIMBAD query result: tau Her -- Pulsating variable Star, Centre de Données astronomiques de Strasbourg, retrieved 2010-06-10 
  2. ^ a b Mermilliod, J.-C. (1986), Compilation of Eggen's UBV data, transformed to UBV (unpublished) (PDF), SIMBAD, Bibcode:1986EgUBV........0M 
  3. ^ Perryman, M. A. C.; et al. (1997), "The Hipparcos Catalogue", Astronomy & Astrophysics, 323: L49–L52, Bibcode:1997A&A...323L..49P 
  4. ^ a b c d e f Kaler, James B., "TAU HER (Tau Herculis)", stars, University of Illinois, retrieved 2010-06-10 
  5. ^ a b c Fitzpatrick, E. L.; Massa, D. (March 2005), "Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry", The Astronomical Journal, 129 (3): 1642–1662, arXiv:astro-ph/0412542free to read, Bibcode:2005AJ....129.1642F, doi:10.1086/427855 
  6. ^ Smith, K. C.; Dworetsky, M. M. (1993), "Elemental Abundances in Normal Late B-Stars and Hgmn-Stars from Co-Added IUE Spectra - Part One - Iron Peak Elements", Astronomy and Astrophysics, 274 (2): 335, Bibcode:1993A&A...274..335S 
  7. ^ Royer, F.; et al. (2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i in the northern hemisphere", Astronomy and Astrophysics, 393 (3): 897–911, arXiv:astro-ph/0205255free to read, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943 
  8. ^ Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14. 
  9. ^ (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.
  10. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 26 日