Eta Herculis

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η Her
Hercules constellation map visualization.PNG
The η star in the "Keystone" asterism
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 16h 42m 53.7653s[1]
Declination 38° 55′ 20.116″[1]
Apparent magnitude (V) 3.487[1]
Spectral type G7.5 IIIb[1]
U−B color index -0.58
B−V color index -0.91[2]
Radial velocity (Rv) 8.3[1] km/s
Proper motion (μ) RA: 35.58[1] mas/yr
Dec.: -84.98[1] mas/yr
Parallax (π) 29.11 ± 0.52[3] mas
Distance 112 ± 2 ly
(34.4 ± 0.6 pc)
Absolute magnitude (MV) +0.84[4]
Mass 2.13[4] M
Radius 8.9 ± 0.3[5] R
Luminosity 50[6] L
Temperature 4,900[6] K
Metallicity [Fe/H] -0.28[7] dex
Rotational velocity (v sin i) 8[8] km/s
Age 1[6] Gyr
Other designations
η Her, 44 Her, HR 6220, BD -39° 3029, HD 150997, FK5 626, HIP 81833, SAO 65504, GC 22502, CCDM J16428+3855A
Database references

Coordinates: Sky map 16h 42m 53.80s, +38° 55′ 20.116″

Eta Herculis (η Her, η Herculis) is a fourth-magnitude star in the constellation Hercules.


Eta Herculis is a G-Type star. With a stellar classification G7.5IIIb, it is yet considerably larger having a mass that is 2.3 times solar and a radius 9.8 times.[6] Though it only shines with an apparent magnitude of 3.48, it is part of the "Keystone" asterism, visible overhead in the mid-summer night sky to northern observers, allowing it to be easily recognized. Eta Herculis is 50 times more luminous than the Sun.[6] The Hipparcos satellite mission estimated its distance at roughly 34.4 parsecs[3] from Earth, or 112 light years away.

If one follows the line connecting Eta Herculis with Zeta Herculis one comes across one of the earliest and most stunning globular clusters in the nighttime sky, M13, discovered in 1714 by Edmond Halley.

Eta Herculis is a double star once thought to be part of a binary star system.[6]

See also[edit]


  1. ^ a b c d e f g "* eta Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-06-09. 
  2. ^ Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV data. Bibcode:1986EgUBV........0M. 
  3. ^ a b Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; et al. (July 1997). "The HIPPARCOS Catalogue". Astronomy and Astrophysics. 323: L49–L52. Bibcode:1997A&A...323L..49P. 
  4. ^ a b Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics, 361: 614–628, Bibcode:2000A&A...361..614P 
  5. ^ Nordgren, Tyler E.; et al. (December 1999), "Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer", The Astronomical Journal, 118 (6): 3032–3038, Bibcode:1999AJ....118.3032N, doi:10.1086/301114 
  6. ^ a b c d e f Kaler, James B. "ETA HER (Eta Herculis)". Stars. University of Illinois. Retrieved 2010-06-09. 
  7. ^ Soubiran, C.; Bienaymé, O.; Mishenina, T. V.; Kovtyukh, V. V. (2008). "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants". Astronomy and Astrophysics. 480 (1): 91–101. arXiv:0712.1370Freely accessible. Bibcode:2008A&A...480...91S. doi:10.1051/0004-6361:20078788. 
  8. ^ Bernacca, P. L.; Perinotto, M. (1970). "A catalogue of stellar rotational velocities". Contributi Osservatorio Astronomico di Padova in Asiago. 239. Bibcode:1970CoAsi.239....1B. 

External links[edit]