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Location of β Centauri (circled) |
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Centaurus |
| Right ascension | 14h 03m 49.40535s[1] |
| Declination | –60° 22′ 22.9266″[1] |
| Apparent magnitude (V) | 0.60 |
| Astrometry | |
| Radial velocity (Rv) | +5.9[2] 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) |
| Characteristics | |
| Spectral type | B1 III[3] |
| U−B color index | –0.98[4] |
| B−V color index | –0.22[4] |
| Variable type | β Cep |
| Details | |
| Mass | 10.7 ± 0.1[5] / 10.3 ± 0.1[5] M☉ |
| Surface gravity (log g) | 3.5 ± 0.4[5] |
| Luminosity | 41,700[3] L☉ |
| Temperature | 25,000 ± 2,000[5] K |
| Age | (14.1 ± 0.6) × 106[5] years |
| Other designations | |
| Database references | |
| SIMBAD | data |
Beta Centauri (β Cen, β Centauri), also known as Hadar or Agena, is the second brightest star in the constellation Centaurus and the tenth brightest star in the night sky. Beta Centauri is a B1 III blue-white giant star that the astrometric Hipparcos satellite calculates as about 525 light-years (161 parsecs) from the solar system. More recent estimates place the distance of the system to closer to 349 ly (107 pc). It is a Beta Cephei variable, which means it is a short-period pulsating variable star.[3]
The name Hadar comes from the Arabic word for "ground / soil / earth" (from أل أرض - al ardh)[6] or "civilation" (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).
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 357.0 days at an eccentricity of about 0.81.[8][5]
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. Coordinates: 14h 03m 49.4s, −60° 22′ 23″
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