Epoch J2000 Equinox J2000
|Right ascension||14h 03m 49.40535s|
|Declination||–60° 22′ 22.9266″|
|Apparent magnitude (V)||0.60|
|Radial velocity (Rv)||+5.9 km/s|
|Proper motion (μ)||RA: –33.27 mas/yr
Dec.: –23.16 mas/yr
|Parallax (π)||9.35 ± 0.50 mas|
|Distance||350 ± 20 ly
(107 ± 6 pc)
|Spectral type||B1 III|
|U−B color index||–0.98|
|B−V color index||–0.22|
|Variable type||β Cep|
|Mass||10.7 ± 0.1 / 10.3 ± 0.1 M☉|
|Surface gravity (log g)||3.5 ± 0.4|
|Temperature||25,000 ± 2,000 K|
|Age||(14.1 ± 0.6) × 106 years|
Beta Centauri (β Cen, β Centauri) is a star system in the southern constellation of Centaurus. With an apparent visual magnitude of 0.60, it is 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 word for "ground / soil / earth" (from أل أرض - al ardh) or "civilization" (from ألحضارة - al hidaara), while the name Agena comes from Latin words for "the knee". The Chinese name for the star is 马腹一 (Mandarin: mǎ fù yī, the First Star of the Horse's Abdomen).
Based upon parallax measurements from the astrometric Hipparcos satellite, the distance to this system is about 350 light-years (110 parsecs). The spectrum matches a star with a stellar classification of B1 III, with the luminosity class of III indicating this is a giant star that has exhausted the hydrogen at its core and evolved away from the main sequence. It is a Beta Cephei variable star with a pulsation period of 0.157 days.
In 1935, Joan Voûte identified Beta Centauri as a double star, 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 slightly. This would indicate that the orbital period is very long, if the pair are actually gravitationally associated.
Based on the variable radial velocity of this star, in 1967 it was suggested that the primary is a double-lined spectroscopic binary. This was confirmed in 1999. The primary consists of a pair of stars with nearly identical mass that orbit each other over a period of 357 days with a large eccentricity of about 0.81. The pair are separated by a mean distance of roughly 4 astronomical units.
Cultural significance 
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.
The indigenous Boorong people of northwestern Victoria named it as Bermbermgle (together with α Cen), two brothers who were noted for their courage and destructiveness, and who spear and kill Tchingal, "The Emu" (Coalsack Nebula). The two brothers in Wotjobaluk people is Bram-bram-bult.
- 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
- Hogg, A. R. (1958), "Photometric observations of 244 bright stars", Mount Stromlo Observatory Mimeogram 2, Bibcode:1958MtSOM...2....1H
- Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, retrieved 2009-09-10
- 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
- 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
- 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
- "V* bet Cen -- Variable Star of beta Cep type", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2011-12-19
- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 29 日
- 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
- Perryman, Michael (2010), The Making of History's Greatest Star Map, Heidelberg: Springer-Verlag, doi:10.1007/978-3-642-11602-5
- 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
- Kyselka, Will; Lanterman, Ray E. (1976), North Star to Southern Cross, University of Hawaii Press, p. 59, ISBN 0-8248-0419-8
- Hamacher, Duane W.; Frew, David J. (2010). "An Aboriginal Australian Record of the Great Eruption of Eta Carinae". Journal of Astronomical History & Heritage 13 (3): 220–34.
- Stanbridge, WM (1857). "On the Astronomy and Mythology of the Aboriginies of Victoria". Transactions Philosophical Institiute Victoria 2: 137–140.
- Kaler, James B., "HADAR (Beta Centauri)", Stars (University of Illinois), retrieved 2011-12-19