Alpha Herculis

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Alpha Herculis
Hercules Historical View.png
Historical view of the Hercules constellation showing Rasalgethi as the α star and "Head of the Kneeler"
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 17h 14m 38.853s[1]
Declination +14° 23′ 25.0″[1]
Apparent magnitude (V) 3.350[1] (2.7 - 4.0[2])
Right ascension 17h 14m 39.181s[1]
Declination +14° 23′ 23.98″[1]
Apparent magnitude (V) 5.322[1]
Evolutionary stage AGB[3]
Spectral type M5 Ib-II[3]
U−B color index +1.01[4]
B−V color index +1.45[4]
Variable type SRc[2]
Spectral type G8III + A9IV-V[3]
Proper motion (μ) RA: -6.71[5][6][7] mas/yr
Dec.: 32.78[5][6][7] mas/yr
Parallax (π) 9.07 ± 1.32[5][6] mas
Distance approx. 360 ly
(approx. 110 pc)
Absolute magnitude (MV) −2.3[8] + 1.8 + 2.8[9]
Mass 2.5 M
Radius 264 - 303 R
Luminosity 7,244 - 9,333 L
Surface gravity (log g) −0.41 ± 0.19[10] cgs
Temperature 3,155 - 3,365 K
Mass ~2.5 M
Luminosity 126 L
Temperature 4,900 K
Mass ~2 M
Luminosity 26 L
Temperature 7,350 K
Age 0.41 - 1.25 Gyr
Other designations
Ras Algethi, Rasalgethi, α Her, 64 Her, BD+14°3207, HIP 84345, CCDM J17146+1424, AAVSO 1710+14
A: HD 156014, HR 6406, SAO 102680
B: HD 156015, HR 6407, SAO 102681
Database references

Alpha Herculis (α Herculis, abbreviated Alpha Her, α Her), also designated 64 Herculis, is a multiple star system in the constellation of Hercules. When viewed through a telescope, this system is resolved into a number of components, the brightest one of which has been named Rasalgethi.[11]


α Herculis (Latinised to Alpha Herculis) is the system's Bayer designation and 64 Herculis its Flamsteed designation. The two components are designated α¹ Herculis (the brightest of the two) and α² Herculis. The latter is itself a binary star and all three stars are sometimes designated α Herculis A, Ba and Bb, respectively.[12]

The system bore the traditional name Rasalgethi or Ras Algethi (Arabic: رأس الجاثي ra‘is al-jāthī‎‎ 'Head of the Kneeler').[13] 'Head' comes from the fact that in antiquity Hercules was depicted upside down on maps of the constellation. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[15] included a table of the first two batches of names approved by the WGSN; which included Rasalgethi for α¹ Herculis.

The term ra's al-jaθiyy or Ras al Djathi appeared in the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, which was translated into Latin as Caput Ingeniculi.[16]

In Chinese astronomy, Rasalgethi is called 帝座, Pinyin: Dìzuò, meaning 'Emperor's Seat', this star is marking itself and stands alone in the center of the Emperor's Seat asterism, Heavenly Market enclosure (see : Chinese constellations).[17] 帝座 (Dìzuò) was westernized into Ti Tso by R.H. Allen, with the same meaning [18]


α¹ and α² Herculis are more than 500 astronomical units apart, with an estimated orbital period of approximately 3600 years. α¹ is a relatively massive red bright giant. α²'s two components are a primary yellow giant star and a secondary, yellow-white dwarf star in a 51.578 day orbit.

α¹ Herculis is an asymptotic giant branch (AGB) star, a luminous red giant that has both hydrogen and helium shells around a degenerate carbon-oxygen core. Its angular diameter has been measured with an interferometer as 34 ± 0.8 mas, or 0.034 arcseconds.[19] At an estimated distance of 110 parsecs from the Sun determined by Hipparcos,[5][6][20] this corresponds to a radius of about 280 million kilometers (or 170 million miles), which is roughly 400 R or 1.87 AU.[21] If Rasalgethi were at the center of the Solar System its radius would extend past the orbit of Mars at 1.5 AU but not quite as far as the asteroid belt. The red giant is estimated to have started its life with about 2.175-3.250 M.[3] Like most type M stars near the end of their lives, Rasalgethi is experiencing a high degree of stellar mass loss creating a sparse, gaseous envelope that extends at least 90 astronomical units.[22]

See also[edit]



  1. ^ a b c d e f Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862. 
  2. ^ a b Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S. 
  3. ^ a b c d e Moravveji, Ehsan; Guinan, Edward F.; Khosroshahi, Habib; Wasatonic, Rick (2013). "The Age and Mass of the α Herculis Triple-star System from a MESA Grid of Rotating Stars with 1.3 <= M/M ⊙ <= 8.0". The Astronomical Journal. 146 (6): 148. arXiv:1308.1632Freely accessible. Bibcode:2013AJ....146..148M. doi:10.1088/0004-6256/146/6/148. 
  4. ^ a b Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D. 
  5. ^ a b c d 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 
  6. ^ a b c d van Leeuwen, F (November 2007). "Hipparcos, the New Reduction". Astronomy and Astrophysics. Centre de Données astronomiques de Strasbourg. 474 (2): 653. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  7. ^ a b "SIMBAD query result:NAME RASALGETHI -- Semi-regular pulsating Star". Centre de Données astronomiques de Strasbourg. Retrieved 2010-09-26. 
  8. ^ Huang, W.; Wallerstein, G.; Stone, M. (2012). "A catalogue of Paschen-line profiles in standard stars". Astronomy & Astrophysics. 547: A62. arXiv:1210.7893Freely accessible. Bibcode:2012A&A...547A..62H. doi:10.1051/0004-6361/201219804. 
  9. ^ Reimers, D. (1977). "On the absolute scale of mass-loss in red giants. I - Circumstellar absorption lines in the spectrum of the visual companion of Alpha-1 HER". Astronomy and Astrophysics. 61: 217. Bibcode:1977A&A....61..217R. 
  10. ^ Schröder, K.-P.; Cuntz, M. (April 2007), "A critical test of empirical mass loss formulas applied to individual giants and supergiants", Astronomy and Astrophysics, 465 (2): 593–601, arXiv:astro-ph/0702172Freely accessible, Bibcode:2007A&A...465..593S, doi:10.1051/0004-6361:20066633 
  11. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  12. ^ Tokovinin, A. A. (1997). "MSC - a catalogue of physical multiple stars". Astronomy & Astrophysics Supplement Series. 124: 75. Bibcode:1997A&AS..124...75T. doi:10.1051/aas:1997181. 
  13. ^ Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14. 
  14. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. 
  15. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016. 
  16. ^ 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 (8): 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429. 
  17. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 25 日
  18. ^ Richard Hinckley Allen: Star Names — Their Lore and Meaning: Hercules
  19. ^ Benson, J. A.; Dyck, H. M.; Mason, W. L.; Howell, R. R.; Ridgway, S. T.; et al. (December 1991). "The infrared angular diameter of Alpha Herculis measured with a Michelson interferometer". Astronomical Journal. 102: 2091–2097. Bibcode:1991AJ....102.2091B. doi:10.1086/116033. 
  20. ^ Perryman, Michael (2010), The Making of History's Greatest Star Map, Astronomers’ Universe, Heidelberg: Springer-Verlag, doi:10.1007/978-3-642-11602-5, ISBN 978-3-642-11601-8 
  21. ^ To determine Rasalgethi's radius in terms of solar units, the calculations begin with the formula for angular diameter as follows:
    where δ equals Rasalgethi's angular diameter in arcseconds, dR the star's diameter in AU, and DR the Distance from Earth in parsecs. If one knows the angular diameter and the Distance, then one can solve for dR as follows:
    To obtain Rasalgheti's radius:
    Converting into Solar units, 1 AU = 149,597,871 km and the mean radius of the Sun = 696,000 km, hence the calculation:
  22. ^ Deutsch, Armin J. (March 1956). "The Circumstellar Envelope of Alpha Herculis". Astrophysical Journal. 123: 210–227. Bibcode:1956ApJ...123..210D. doi:10.1086/146152. 

External links[edit]

Coordinates: Sky map 17h 14m 38.858s, +14° 23′ 25.20″