Epsilon Canis Majoris

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ε Canis Majoris
Canis Major constellation map.svg
Red circle.svg

Location of ε Canis Majoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Canis Major
Right ascension 06h 58m 37.6s
Declination –28° 58′ 19″
Apparent magnitude (V) 1.50[1]
Spectral type B2II[2]
U−B color index –0.93[1]
B−V color index –0.21[1]
Radial velocity (Rv) +27.3 km/s
Proper motion (μ) RA: +2.63[3][4] mas/yr
Dec.: +2.29[3][4] mas/yr
Parallax (π) 7.57 ± 0.57[3][4] mas
Distance 430 ± 30 ly
(132 ± 10 pc)
Absolute magnitude (MV) –4.8[5]
Mass 12.6 ± 1.0[2] M
Radius 13.9[6] R
Luminosity 38,700[7] L
Surface gravity (log g) 3.39[7] cgs
Temperature 22,900[7] K
Rotational velocity (v sin i) 25[8] km/s
Age 22.5 ± 2.6[2] Myr
Other designations
Adhara, Adharaz, Undara, ε CMa, 21 CMa, ADS 5654, CD −28° 3666, FK5 268, HD 52089, HIP 33579, HR 2618, SAO 172676.
Database references

Epsilon Canis Majoris (ε Canis Majoris, abbreviated Epsilon CMa, ε CMa), also named Adhara,[9] is a binary star and, despite being designated 'epsilon', the second brightest star in the constellation of Canis Major and one of the brightest stars in the night sky. About 4.7 million years ago, it was the brightest star in the sky, with an apparent magnitude of -3.99.


ε Canis Majoris (Latinised to Epsilon Canis Majoris) is the star's Bayer designation.

It bore the traditional name Adhara (sometimes spelled Adara), derived from the Arabic word عذارى ‘aðāra’, "virgins". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[10] to catalogue and standardize proper names for stars. The WGSN approved the name Adhara for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[9]

In the 17th century catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Aoul al Adzari (أول العذاري - awwal al-adhara), which was translated into Latin as Prima Virginum, meaning First of the Virgins.[11] Along with Delta Canis Majoris (Wezen), Eta Canis Majoris (Aludra) and Omicron² Canis Majoris (Thanih al Adzari), these stars were Al ʽAdhārā (العذاري), 'the Virgins'.[12][13]

In Chinese, 弧矢 (Hú Shǐ), meaning Bow and Arrow,[14] refers to an asterism consisting of Epsilon Canis Majoris, Delta Canis Majoris, Eta Canis Majoris, HD 63032, HD 65456, Omicron Puppis, k Puppis, Kappa Canis Majoris and Pi Puppis. Consequently, Epsilon Canis Majoris itself is known as 弧矢七 (Hú Shǐ qī, English: the Seventh Star of Bow and Arrow).[15]


USS Adhara (AK-71) was a United States Navy Crater class cargo ship named after the star.


Adhara is a binary star, estimated by the Hipparcos astrometry satellite to lie about 430 light years away from Earth.[3][4][16] The main star possesses an apparent magnitude of +1.5 and belongs to the spectral classification B2. Its color is blue or blueish-white, due to the surface temperature of 22,200K. It emits a total radiation equal to 38,700 times that of the Sun. This star is the brightest known extreme ultraviolet source in the night sky.[17] It is the strongest source of photons capable of ionizing hydrogen atoms in interstellar gas near the Sun, and is very important in determining the ionization state of the Local Interstellar Cloud.[18]

The +7.5 magnitude companion star (the absolute magnitude amounts to +1.9) is at 7.5" away with a position angle of 161° of the main star. Despite the relatively large angular distance the components can only be resolved in large telescopes, since the main star is approximately 250 times brighter than its companion.

A few million years ago, Adhara was much closer to the Sun than it is at present, causing it to be a much brighter star in the night sky. About 4,700,000 years ago, Adhara was 34 light years from the Sun, and was the brightest star in the sky with a magnitude of –3.99. No other star has attained this brightness since, nor will any other star attain this brightness for at least five million years.[19]

Modern legacy[edit]

Adhara appears on the national flag of Brazil, symbolising the state of Tocantins.[20]

Adhara also appears as a physical character in the 2007 animated film, Nocturna, as the main character Tim's favourite star.[21]

See also[edit]


  1. ^ a b c 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: 0. Bibcode:2002yCat.2237....0D. 
  2. ^ a b c Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (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, Bibcode:2011MNRAS.410..190T, arXiv:1007.4883Freely accessible, doi:10.1111/j.1365-2966.2010.17434.x 
  3. ^ a b c d Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; Bastian, U.; Bernacca, P. L.; Crézé, M.; Donati, F.; Grenon, M.; Grewing, M.; Van Leeuwen, F.; Van Der Marel, H.; Mignard, F.; Murray, C. A.; Le Poole, R. S.; Schrijver, H.; Turon, C.; Arenou, F.; Froeschlé, M.; Petersen, C. S.; et al. (1997). "The HIPPARCOS Catalogue". Astronomy and Astrophysics. 323: L49–L52. Bibcode:1997A&A...323L..49P. 
  4. ^ a b c d van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357 
  5. ^ Snow, Theodore P.; Lamers, Henny J. G. L. M.; Lindholm, Douglas M.; Odell, Andrew P. (1994). "An atlas of ultraviolet P Cygni profiles". The Astrophysical Journal Supplement Series. 95: 163. Bibcode:1994ApJS...95..163S. doi:10.1086/192099. 
  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. ^ a b c Lyubimkov, L. S.; Rostopchin, S. I.; Lambert, D. L. (June 2004), "Surface abundances of light elements for a large sample of early B-type stars - III. An analysis of helium lines in spectra of 102 stars", Monthly Notices of the Royal Astronomical Society, 351 (2): 745–767, Bibcode:2004MNRAS.351..745L, doi:10.1111/j.1365-2966.2004.07825.x 
  8. ^ 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. 
  9. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  10. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  11. ^ 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): 429–438. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429. 
  12. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications. p. 130. ISBN 0-486-21079-0. 
  13. ^ ε CMa as Aoul al Adzari or Prima Virginum (First of the Virgins), Omicron² Canis Majoris as Thanih al Adzari or Secunda Virginum (Second of the Virgins) and Delta Canis Majoris as Thalath al Adzari or Tertia Virginum (Third of the Virgins). Eta Canis Majoris should be Rabah al Adzari or Quarta Virginum (Fourth of the Virgins) consistently, but it was given by the name Aludra, meaning Virgin (same meaning with Adhara or Al ʽAdhārā)
  14. ^ 弧矢 (Hú Shǐ) is westernized into Koo She. R.H. Allen opined 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 a 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 (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日.
  15. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日
  16. ^ Perryman, Michael (2010), "The Making of History's Greatest Star Map", The Making of History's Greatest Star Map:, Astronomers’ Universe, Heidelberg: Springer-Verlag, Bibcode:2010mhgs.book.....P, ISBN 978-3-642-11601-8, doi:10.1007/978-3-642-11602-5 
  17. ^ Wilkinson, E.; Green, J. C.; McLean, R.; Welsh, B. (1996). "Extreme Ultraviolet Spectrum of ɛ Canis Majoris Between 600-920 Å". Bull. Am. Astron. Soc. 28 (2): 915. Bibcode:1996BAAS...28..915W. 
  18. ^ Vallerga, J. V.; Welsh, B. Y. (1995). "Epsilon Canis Majoris and the ionization of the local cloud". Astrophys. J. 444: 702–707. Bibcode:1995ApJ...444..702V. doi:10.1086/175643. 
  19. ^ Tomkin, Jocelyn (April 1998). "Once and Future Celestial Kings" (PDF). Sky and Telescope. 95 (4): 59–63. Bibcode:1998S&T....95d..59T. 
  20. ^ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website.  Archived March 30, 2014, at the Wayback Machine.
  21. ^ "Nocturna (2007)". Internet Movie Database (IMDB). 

Coordinates: Sky map 06h 58m 37.6s, −28° 58′ 19″