Beta Centauri

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This article is about β Centauri and should not to be confused with Alpha Centauri B. For B Centauri, see B Centauri. For b Centauri, see HD 129116.
β Centauri
Diagram showing star positions and boundaries of the Centauri constellation and its surroundings
Cercle rouge 100%.svg

Location of β Centauri (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Centaurus
Right ascension 14h 03m 49.40535s[1]
Declination –60° 22′ 22.9266″[1]
Apparent magnitude (V) 0.60[2]
Radial velocity (Rv) +5.9[3] km/s
Proper motion (μ) RA: –33.27[1] mas/yr
Dec.: –23.16[1] mas/yr
Parallax (π) 9.35 ± 0.50[1] mas
Distance 350 ± 20 ly
(107 ± 6 pc)
Spectral type B1 III[4]
U−B color index –0.98[2]
B−V color index –0.22[2]
Variable type β Cep
Mass 10.7 ± 0.1[5] / 10.3 ± 0.1[5] M
Luminosity 41,700[4] L
Surface gravity (log g) 3.5 ± 0.4[5] cgs
Temperature 25,000 ± 2,000[5] K
Age (14.1 ± 0.6) × 106[5] years
Other designations
Agena, Hadar,[6] HR 5267, HD 122451, CD−59°5365, LHS 51, SAO 252582, FK5 518 , HIP 68702, GC 18971, CCDM J14038-6022.[7]
Database references

Beta Centauri (β Cen, β Centauri) is a trinary star system in the southern constellation of Centaurus. The system's combined apparent visual magnitude of 0.60, makes it the second brightest star in the constellation Centaurus and the tenth brightest star in the night sky. It has the traditional names Hadar and Agena. The name Hadar comes from the Arabic حضار (the root's meaning is "to be present" or "on the ground" or "settled, civilized area"[8]), while the name Agena may ultimately be derived from the Latin gena 'knees'. The Chinese name for the star is 马腹一 (Mandarin: mǎ fù yī, the First Star of the Horse's Abdomen).[9]


The Beta Centauri system has three components: Beta Centauri A1, A2 and B.

According to parallax measurements from the astrometric Hipparcos satellite,[10][11] the distance to this system is about 350 light-years (110 parsecs).[1] The spectrum matches a star with a stellar classification of B1 III,[4] with the luminosity class of III indicating Beta Centauri A1 and A2 are both giant stars that have exhausted the hydrogen at its core and evolved away from the main sequence. They are both Beta Cephei variable stars with a pulsation period of 0.157 days.[4][12]

In 1967, Beta Centauri's observed periodic variation in radial velocity suggested that Beta Centauri A is a double-lined spectroscopic binary. This was confirmed in 1999. The primary consists of a pair of stars, (A1 and A2) with nearly identical mass that orbit each other over a period of 357 days with a large eccentricity of about 0.81.[5][13] The pair are separated by a mean distance of roughly 4 astronomical units.[4]

In 1935, Joan Voûte identified Beta Centauri B, giving it the identifier VOU 31. The companion is separated from the primary by 1.3 seconds of arc, and has remained so since the discovery, although the position angle has changed six degrees since. Beta Centauri B orbits A1 and A2 at .6 light years, or 100k AUs, with a period of roughly 1500 years. Beta Centauri B is a B1 Dwarf with an apparent magnitude of 3.7, and an absolute magnitude of -1.5, similar to that of Achernar.[14]

Cultural significance[edit]

Beta Centauri is well known in the Southern Hemisphere as the inner of the two "Pointers" to the Southern Cross. A line made from the other pointer, Alpha Centauri, through Beta Centauri leads to within a few degrees of Gacrux, the star at the top of the cross. Using Gacrux, a navigator can draw a line with Acrux to effectively determine south.[15]

The indigenous Boorong people of northwestern Victoria named it as Bermbermgle (together with α Cen),[16] two brothers who were noted for their courage and destructiveness, and who spear and kill Tchingal, "The Emu" (Coalsack Nebula).[17] The two brothers in Wotjobaluk people is Bram-bram-bult.[16]


  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 
  2. ^ a b c Hogg, A. R. (1958), "Photometric observations of 244 bright stars", Mount Stromlo Observatory Mimeogram 2, Bibcode:1958MtSOM...2....1H 
  3. ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, retrieved 2009-09-10 
  4. ^ a b c d e Raassen, A. J. J. et al. (July 2006), "XMM-Newton observations of β Centauri (B1 III): The temperature structure in the hot plasma and the photosphere-wind connection", Astronomy and Astrophysics 437 (2): 599–609, Bibcode:2005A&A...437..599R, doi:10.1051/0004-6361:20052650 
  5. ^ a b c d e f Ausseloos, M. et al. (August 2006), "High-precision elements of double-lined spectroscopic binaries from combined interferometry and spectroscopy. Application to the β Cephei star β Centauri", Astronomy and Astrophysics 455 (1): 259–269, arXiv:astro-ph/0605220, Bibcode:2006A&A...455..259A, doi:10.1051/0004-6361:20064829 
  6. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 154, ISBN 0-486-21079-0, retrieved 2010-12-12 
  7. ^ "V* bet Cen -- Variable Star of beta Cep type", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2011-12-19 
  8. ^ Hans Wehr, A dictionary of modern written Arabic, 1961
  9. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 29 日
  10. ^ Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J. et al. (July 1997), "The Hipparcos Catalogue", Astronomy and Astrophysics 323: L49–L52, Bibcode:1997A&A...323L..49P 
  11. ^ Perryman, Michael (2010), The Making of History's Greatest Star Map, Heidelberg: Springer-Verlag, doi:10.1007/978-3-642-11602-5 
  12. ^ Sterken, Christiaan; Jerzykiewicz, Mikolaj (1993). "Beta Cephei stars from a photometric point of view". Space Science Reviews 62 (1-2): 95–171. Bibcode:1993SSRv...62...95S. ISSN 0038-6308. 
  13. ^ Ausseloos, M.; Aerts, C.; Uytterhoeven, K. (2002), "A Study of the Orbital and Intrinsic Variability of the Double-Lined Spectroscopic Binary β Centauri", in Aerts, Conny; Bedding, Timothy R.; Christensen-Dalsgaard, Jørgen, Radial and Nonradial Pulsations as Probes of Stellar Physics, ASP Conference Proceedings 259, p. 86, Bibcode:2002ASPC..259...86A 
  14. ^
  15. ^ Kyselka, Will; Lanterman, Ray E. (1976), North Star to Southern Cross, University of Hawaii Press, p. 59, ISBN 0-8248-0419-8 
  16. ^ a b Hamacher, Duane W.; Frew, David J. (2010). "An Aboriginal Australian Record of the Great Eruption of Eta Carinae" (PDF). Journal of Astronomical History & Heritage 13 (3): 220–34. 
  17. ^ Stanbridge, WM (1857). "On the Astronomy and Mythology of the Aboriginies of Victoria" (PDF). Transactions Philosophical Institute Victoria 2: 137–140. 

External links[edit]

Coordinates: Sky map 14h 03m 49.4s, −60° 22′ 23″