Eta Canis Majoris

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η Canis Majoris
Canis Major constellation map.svg
Red circle.svg
Location of η Canis Majoris (circled)
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[4]
Radial velocity (Rv)41.1[5] km/s
Proper motion (μ) RA: −4.14[1] mas/yr
Dec.: 5.81[1] mas/yr
Parallax (π)1.64 ± 0.40 mas[1]
Distanceapprox. 2,000 ly
(approx. 600 pc)
Absolute magnitude (MV)−7.0[6]
Mass18.19[7] M
Radius54[8] R
Luminosity135,000 - 174,000[8] L
Surface gravity (log g)2.00[8] cgs
Temperature15,000 - 16,000[8] K
Rotational velocity (v sin i)40[8] km/s
Age8.3[9] Myr
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 Canis Majoris, abbreviated Eta CMa, η CMa), also named Aludra /əˈldrə, əˈljdrə/,[10] is a star in the constellation of Canis Major. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[11]


η Canis Majoris (Latinised to Eta Canis Majoris) is the star's Bayer designation.

The traditional name Aludra originates from the Arabic: العذراء al-adhraa, 'the virgin'. This star, along with Epsilon Canis Majoris (Adhara), Delta Canis Majoris (Wezen) and Omicron2 Canis Majoris (Thanih al Adzari), were Al 'Adhārā (العذاري), 'the Virgins'.[12] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[14] included a table of the first two batches of names approved by the WGSN; which included Aludra for this star.

In Chinese, 弧矢 (Hú Shǐ), meaning Bow and Arrow,[15] refers to an asterism consisting of Eta Canis Majoris, Delta Canis Majoris, HD 63032, HD 65456, Omicron Puppis, k Puppis, Epsilon Canis Majoris, Kappa Canis Majoris and Pi Puppis. Consequently, Eta Canis Majoris itself is known as 弧矢二 (Hú Shǐ èr, English: the Second Star of Bow and Arrow).[16]


A light curve for Eta Canis Majoris, plotted from Hipparcos data[17]

A blue-white supergiant, Eta CMa has been used as a standard for the spectral type of B5Ia.[18]

Eta CMa shines brightly in the skies in spite of a large distance from Earth due to being intrinsically many times brighter than the Sun. It has a luminosity over 100,000 times and a radius around 54 times that of the Sun. It has only been around a fraction of the time the Sun has, less than 10 million years, 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.[citation needed]

Eta CMa 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.[4][19]


Both USS Aludra (AF-55), an Alstede-class stores ship, and USS Aludra (AK-72), a Crater-class cargo ship, were U.S. 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. S2CID 18759600.
  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. ^ Prinja, R. K.; Massa, D. L. (October 2010), "Signature of wide-spread clumping in B supergiant winds", Astronomy and Astrophysics, 521: L55, arXiv:1007.2744, Bibcode:2010A&A...521L..55P, doi:10.1051/0004-6361/201015252, S2CID 59151633
  4. ^ a b Kazarovets, E. V.; Samus, N. N.; Durlevich, O. V.; Frolov, M. S.; Antipin, S. V.; Kireeva, N. N.; Pastukhova, E. N. (1999). "The 74th Special Name-list of Variable Stars". Information Bulletin on Variable Stars. 4659: 1. Bibcode:1999IBVS.4659....1K.
  5. ^ Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W
  6. ^ 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 (3): 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601
  7. ^ Kervella, Pierre; Arenou, Frédéric; Thévenin, Frédéric (2022). "Stellar and substellar companions from Gaia EDR3. Proper-motion anomaly and resolved common proper-motion pairs". Astronomy and Astrophysics. 657: 657. arXiv:2109.10912. Bibcode:2022A&A...657A...7K. doi:10.1051/0004-6361/202142146. S2CID 237605138.
  8. ^ a b c d e Haucke, M.; Cidale, L. S.; Venero, R. O. J.; Curé, M.; Kraus, M.; Kanaan, S.; Arcos, C. (2018). "Wind properties of variable B supergiants. Evidence of pulsations connected with mass-loss episodes". Astronomy and Astrophysics. 614. arXiv:1902.01341. Bibcode:2018A&A...614A..91H. doi:10.1051/0004-6361/201731678. S2CID 126150688.
  9. ^ Tetzlaff, N.; et al. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873.
  10. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  11. ^ 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
  12. ^ 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
  13. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  14. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  15. ^ 弧矢 (Hú Shǐ) is westernized into Koo She. R.H. Allen had opinion that Koo She refers to the asterism including Delta Velorum and Omega Velorum. AEEA opinion is, Delta Velorum is member of 天社 (Tiān Shè), meaning Celestial Earth God's Temple asterism, and Omega 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 Eta Carinae. See Richard Hinckley Allen: Star Names — Their Lore and Meaning: Argo Navis and (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日.
  16. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日
  17. ^ "Light Curve". Hipparcos ESA. ESA. Retrieved 12 August 2022.
  18. ^ Morgan, W. W.; Abt, Helmut A.; Tapscott, J. W. (1978). Revised MK Spectral Atlas for stars earlier than the sun. Yerkes Observatory, University of Chicago.
  19. ^ Watson, Christopher (3 May 2013). "Eta Canis Majoris". AAVSO Website. American Association of Variable Star Observers. Retrieved 5 February 2014.