Eta Canis Majoris

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Eta Canis Majoris
Eta CMa.jpg

Eta Canis Majoris, a blue Supergiant in Canis Major
Observation data
Epoch J2000      Equinox J2000
Constellation Canis Major
Right ascension 07h 24m 05.70228s[1]
Declination –29° 18′ 11.1798″[1]
Apparent magnitude (V) 2.450[2]
Spectral type B5 Ia[3]
U−B color index −0.708[2]
B−V color index −0.087[2]
Variable type α Cyg[citation needed]
Radial velocity (Rv) 41.1[4] km/s
Proper motion (μ) RA: −4.14[1] mas/yr
Dec.: 5.81[1] mas/yr
Parallax (π) 1.64 ± 0.40[1] mas
Distance approx. 2,000 ly
(approx. 600 pc)
Absolute magnitude (MV) -7.0[5]
Mass 19.19 ± 1.15[6] M
Radius 56.3[5] R
Luminosity 105,442[6] L
Temperature 15,000[3] K
Rotational velocity (v sin i) 50[7] km/s
Other designations
Aludra, 31 Canis Majoris, CD −29° 4328, FK5 283, HD 58350, HIP 35904, HR 2827, SAO 173651.
Database references

Eta Canis Majoris (η CMa, η Canis Majoris) is a star in the constellation Canis Major. It has the traditional name Aludra. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[8]

The name Aludra originates from the Arabic: عذرا al-‘aðrā "the virgin". This star, along with ε CMa (Adhara), δ CMa (Wezen) and ο2 CMa (Thanih al Adzari), were Al ʽAdhārā (ألعذاري), the Virgins.[9]

In Chinese, 弧矢 (Hú Shǐ), meaning Bow and Arrow,[10] refers to an asterism consisting of η Canis Majoris, δ Canis Majoris, HD 63032, HD 65456, ο Puppis, k Puppis, ε Canis Majoris, κ Canis Majoris and π Puppis. Consequently, η Canis Majoris itself is known as 弧矢二 (Hú Shǐ èr, English: the Second Star of Bow and Arrow.)[11]


Aludra shines brightly in the skies in spite of a large distance from Earth due to being intrinsically many times brighter (absolute magnitude) than the Sun. A blue-white supergiant of spectral type B5Ia, Aludra has a luminosity 176,000 times and a diameter around 80 times that of the Sun.[12] It has only been around a fraction of the time our Sun has, yet is already in the last stages of its life. It is still expanding and may become a red supergiant, or perhaps has already passed that phase, but in either case it will become a supernova within the next few million years.

Aludra is classified as an Alpha Cygni type variable star and its brightness varies from magnitude +2.38 to +2.48 over a period of 4.7 days.[13]


Both USS Aludra (AF-55) and USS Aludra (AK-72), a Crater class cargo ship, were United States Navy vessels named after the star.


  1. ^ a b c d e van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b c Alcaino, Gonzalo (June 1969), "The Globular Clusters NGC 2808 and NGC 1851", Astrophysical Journal 156: 853, Bibcode:1969ApJ...156..853A, doi:10.1086/150019 
  3. ^ a b Prinja, R. K.; Massa, D. L. (October 2010), "Signature of wide-spread clumping in B supergiant winds", Astronomy and Astrophysics 521, arXiv:1007.2744, Bibcode:2010A&A...521L..55P, doi:10.1051/0004-6361/201015252 
  4. ^ 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 
  5. ^ a b Underhill, A. B. et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society 189: 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601 
  6. ^ a b Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355 
  7. ^ 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. ^ 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 
  9. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc, p. 130, ISBN 0-486-21079-0, retrieved 2010-12-12 
  10. ^ 弧矢 (Hú Shǐ) is westernized into Koo She. R.H. Allen had opinion that Koo She refers to the asterism including δ Velorum and ω Velorum. AEEA opinion is, δ Velorum is member of 天社 (Tiān Shè), meaning Celestial Earth God's Temple asterism and ω Velorum is not member of any asterisms. 天社 (Tiān Shè) is westernized into Tseen She and R.H.Allen used the term Tseen She for Chinese name of η Carinae. See Richard Hinckley Allen: Star Names — Their Lore and Meaning: Argo Navis and (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日.
  11. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日
  12. ^ Jerzykiewicz, M.; Molenda-Zakowicz, J. (2000). "Empirical Luminosities and Radii of Early-Type Stars after Hipparcos" (PDF). Acta Astronomica 50: 369–80. Bibcode:2000AcA....50..369J. 
  13. ^ Watson, Christopher (3 May 2013). "Eta Canis Majoris". AAVSO Website. American Association of Variable Star Observers. Retrieved 5 February 2014.