Eta Aurigae

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η Aurigae
Diagram showing star positions and boundaries of the Auriga constellation and its surroundings
Cercle rouge 100%.svg

Location of η Aurigae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Auriga
Right ascension 05h 06m 30.89337s[1]
Declination +41° 14′ 04.1127″[1]
Apparent magnitude (V) 3.18[2]
Spectral type B3 V[3]
U−B color index –0.66[4]
B−V color index –0.18[4]
R−I color index –0.17
Radial velocity (Rv) +7.3[2] km/s
Proper motion (μ) RA: +31.45[1] mas/yr
Dec.: –67.87[1] mas/yr
Parallax (π) 13.40 ± 0.20[1] mas
Distance 243 ± 4 ly
(75 ± 1 pc)
Mass 5.4 ± 0.3[5] M
Radius 3.25 ± 0.18[6] R
Luminosity 955[5] L
Surface gravity (log g) 4.13 ± 0.04[6] cgs
Temperature 17,201 ± 173[6] K
Rotational velocity (v sin i) 95[7] km/s
Age 22–55[5] Myr
Other designations
Hoedus II, 10 Aurigae, BD+41° 1058, FK5 185, GC 6226, HD 32630, HIP 23767, HR 1641, SAO 40026.[8]
Database references

Eta Aurigae (η Aur, η Aurigae) is a star in the constellation Auriga. It has the traditional name Haedus II. With an apparent visual magnitude of 3.18,[2] it is visible to the naked eye. Based upon parallax measurements made during the Hipparcos mission, this star is approximately 243 light-years (75 parsecs) distant from the Earth.

Eta Aurigae is a larger star than the Sun, with more than five[5] times the Sun's mass and over three times the Sun's radius.[6] The spectrum of this star matches a stellar classification of B3 V,[3] which is a B-type main sequence star that is generating its energy through the nuclear fusion of hydrogen at its core. It is radiating 955[5] times the Sun's luminosity from its outer atmosphere at an effective temperature of 17,201 K.[6] Based upon its projected rotational velocity of 95,[7] it is spinning with a rotation period of only 1.8 days.[9] Eta Aurigae is around 39 million years old.[5]


Along with ζ Aurigae it represents one of the Kids of the she-goat Capella, from which it gets its Latin traditional name Hoedus II or Haedus II, from the Latin haedus "kid"; Zeta Aurigae is Haedus I. It has the less common traditional name Mahasim, from the Arabic المِعْصَم al-micşam "wrist" (of the charioteer), which it shares with Theta Aurigae. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[3] It has an apparent visual magnitude of 3.18[2] and is located at a distance of around 243 light-years (75 parsecs) from Earth.[1]

In Chinese, (Zhù), meaning Pillars, refers to an asterism consisting of η Aurigae, ε Aurigae, ζ Aurigae, υ Aurigae, ν Aurigae, τ Aurigae, χ Aurigae and 26 Aurigae.[10] Consequently, η Aurigae itself is known as 柱三 (Zhǔ sān, English: the Third Star of Pillars.)[11]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W 
  3. ^ a b c Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society, 25: 1319, Bibcode:1993AAS...183.1710G, retrieved 2012-02-04 
  4. ^ a b Crawford, D. L.; Barnes, J. V.; Golson, J. C. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal, 76: 1058, Bibcode:1971AJ.....76.1058C, doi:10.1086/111220 
  5. ^ a b c d e f Lyubimkov, Leonid S.; et al. (June 2002), "Surface abundances of light elements for a large sample of early B-type stars - II. Basic parameters of 107 stars", Monthly Notices of the Royal Astronomical Society, 333 (1): 9–26, Bibcode:2002MNRAS.333....9L, doi:10.1046/j.1365-8711.2002.05341.x 
  6. ^ a b c d e 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/0412542Freely accessible, Bibcode:2005AJ....129.1642F, doi:10.1086/427855 
  7. ^ a b Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590 
  8. ^ "eta Aur -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-08 
  9. ^ kaler, James B., "HAEDUS II (Eta Aurigae)", Stars, University of Illinois, retrieved 2012-02-09 
  10. ^ (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.
  11. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived January 29, 2011, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.

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