Beta Canis Majoris

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Beta Canis Majoris
Diagram showing star positions and boundaries of the Canis Major constellation and its surroundings
Location of β Canis Majoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Canis Major
Right ascension 06h 22m 41.98535s[1]
Declination −17° 57′ 21.3073″[1]
Apparent magnitude (V) 1.985[2] (1.97 - 2.01[3])
Spectral type B1 II-III[4]
U−B color index −0.99[2]
B−V color index −0.235[2]
Variable type β Cep[5]
Radial velocity (Rv)+33.7[6] km/s
Proper motion (μ) RA: −3.23[1] mas/yr
Dec.: −0.78[1] mas/yr
Parallax (π)6.62 ± 0.22 mas[1]
Distance490 ± 20 ly
(151 ± 5 pc)
Absolute magnitude (MV)−4.1[7]
Mass13.5 ± 0.5[8] M
Radius9.7 ± 1.3[9] R
Luminosity26600[9] L
Surface gravity (log g)3.79 ± 0.20[9] cgs
Temperature25,000[10] K
Metallicity [Fe/H]0.04 ± 0.10[8] dex
Rotational velocity (v sin i)31 ± 5[8] km/s
Age12.4 ± 0.7[8] Myr
Other designations
Mirzam, Murzim, Mirza,[11] 2 Canis Majoris, HR 2294, BD−17°1467, HD 44743, SAO 151428, FK5 243, HIP 30324, GC 8223, CCDM 06227-1757[12]
Database references

Beta Canis Majoris (β Canis Majoris, abbreviated Beta CMa, β CMa), also named Mirzam /ˈmɜːrzəm/,[13] is a star in the southern constellation of Canis Major, the "Great Dog", located at a distance of about 500 light-years (150 parsecs) from the Sun.[1] In the modern constellation it lies at the position of the dog's front leg.


Beta Canis Majoris is the star's Bayer designation. The traditional names Mirzam, Al-Murzim or Murzim,[11] derive from the Arabic (مرزم) for 'The Herald', and probably refers to its position, heralding (i.e., rising before) Sirius in the night sky. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[15] included a table of the first two batches of names approved by the WGSN; which included Mirzam for this star.

In Chinese, 軍市 (Jūn Shì), meaning 'Market for Soldiers', refers to an asterism consisting of β Canis Majoris, Nu3 Canis Majoris, 15 Canis Majoris, Pi Canis Majoris, Omicron1 Canis Majoris and Xi1 Canis Majoris.[16] Consequently, β Canis Majoris itself is known as 軍市一 (Jūn Shì yī, English: the First Star of Market for Soldiers).[17] From this Chinese name arose the name Kuen She.[11]

The Dunhuang Star Chart noted β Canis Majoris as Yeji "Pheasant Cock", though was located about 10 degrees too far north of its correct position.[18]

Beta Canis Majoris was called Oupo by the people of the Tuamotus.[19]


Pulsation cycles[8]
(km s−1)
3.9793 2.7
3.9995 2.6
4.1832 0.7

Mirzam is a Beta Cephei variable that varies in apparent magnitude between +1.97 and +2.01 over a six-hour period, a change in brightness that is too small to be discerned with the naked eye. It exhibits this variation in luminosity because of periodic pulsations in its outer envelope, which follow a complex pattern with three different cycles; all about six hours in length. The two dominant pulsation frequencies have a combined beat period of roughly 50 days. The strongest pulsation mode is a radial first overtone, while the second is non-radial.[8]

A light curve for Beta Canis Majoris, plotted from Hipparcos data[20]

This star has a mass of about 13–14 times the mass of the Sun[8] with 8–11 times the Sun's radius.[9] The effective temperature of the star's outer envelope is about 23,150 K, which is much higher than the Sun's at 5,778 K. The energy emitted at the high temperature of the former is what gives this star a blue-white hue characteristic of a B-type star.[10][21] The estimated age of Mirzam is 12–13 million years, which is long enough for a star of this mass to have evolved into a giant star. The stellar classification of B1 II-III[4] indicates that the spectrum matches a star part way between a giant star and a bright giant.

Beta Canis Majoris is located near the far end of the Local Bubble,[22] a cavity in the local interstellar medium through which the Sun is traveling. Beta Canis Majoris was the brightest star in the night sky around four million years ago, peaking with an apparent magnitude of -3.65, or more than seven times as bright as Sirius today.[23]

In culture[edit]

Mirzam appears on the flag of Brazil, symbolising the state of Amapá.[24]

Murzim (AK-95) was a United States Navy Crater class cargo ship named after one of the star's alternative traditional names.


  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:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600
  2. ^ a b c Cousins, A. W. J. (1972), "UBV Photometry of Some Very Bright Stars", Monthly Notes of the Astronomical Society of Southern Africa, 31: 69, Bibcode:1972MNSSA..31...69C
  3. ^ Balona, L. A.; Bregman, L.; Letsapa, B. A.; Magoro, B. T.; Walsh, S. E. (1996). "The Pulsation Frequencies of beta CMa". Information Bulletin on Variable Stars. 4313: 1. Bibcode:1996IBVS.4313....1B.
  4. ^ a b Abt, Helmut A.; et al. (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590
  5. ^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: 02025. Bibcode:2009yCat....102025S.
  6. ^ Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Washington, Bibcode:1953GCRV..C......0W
  7. ^ Shobbrook, R. R.; Handler, G.; Lorenz, D.; Mogorosi, D. (2006). "Photometric studies of three multiperiodic β Cephei stars: β CMa, 15 CMa and KZ Mus". Monthly Notices of the Royal Astronomical Society. 369 (1): 171–181. arXiv:astro-ph/0603754. Bibcode:2006MNRAS.369..171S. doi:10.1111/j.1365-2966.2006.10289.x. S2CID 18593836.
  8. ^ a b c d e f g Mazumdar, A.; et al. (November 2006), "An asteroseismic study of the β Cephei star β Canis Majoris", Astronomy and Astrophysics, 459 (2): 589–596, arXiv:astro-ph/0607261, Bibcode:2006A&A...459..589M, doi:10.1051/0004-6361:20064980, S2CID 11807580
  9. ^ a b c d Hubrig, S.; et al. (June 2006), "Discovery of magnetic fields in the βCephei star ξ1 CMa and in several slowly pulsating B stars*", Monthly Notices of the Royal Astronomical Society: Letters, 369 (1): L61–L65, arXiv:astro-ph/0604283, Bibcode:2006MNRAS.369L..61H, doi:10.1111/j.1745-3933.2006.00175.x, S2CID 18201908
  10. ^ a b Zorec, J.; et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff", Astronomy and Astrophysics, 501 (1): 297–320, arXiv:0903.5134, Bibcode:2009A&A...501..297Z, doi:10.1051/0004-6361/200811147, S2CID 14969137
  11. ^ a b c Allen, Richard Hinckley (1899), "Star-names and their meanings", New York: 129–130,
  12. ^ "V* bet CMa -- Variable Star of beta Cep type", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-02
  13. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  14. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  15. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  16. ^ (in 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.
  17. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2011-01-30 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  18. ^ Jean-Marc Bonnet-Bidaud; Dr Françoise Praderie & Dr Susan Whitfield (16 June 2009). "The Dunhuang Chinese Sky: A Comprehensive Study Of The Oldest Known Star Atlas". Archived from the original on 2 April 2014.
  19. ^ Makemson 1941, p. 239.
  20. ^ "Light Curve". Hipparcos ESA. ESA. Retrieved 17 February 2022.
  21. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16
  22. ^ Welsh, Barry Y. (1991). "The interstellar tunnel of neutral-free gas toward Beta Canis Majoris". The Astrophysical Journal. 373: 556. Bibcode:1991ApJ...373..556W. doi:10.1086/170074. ISSN 0004-637X.
  23. ^ Tomkin, Jocelyn (April 1998). "Once and Future Celestial Kings". Sky and Telescope. 95 (4): 59–63. Bibcode:1998S&T....95d..59T. – based on computations from HIPPARCOS data. (The calculations exclude stars whose distance or proper motion is uncertain.) PDF[permanent dead link]
  24. ^ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. Archived from the original on 2009-06-28.


  • Makemson, Maud Worcester (1941), The Morning Star Rises: An Account of Polynesian Astronomy, Yale University Press,