Beta Centauri
 Location of β Centauri (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Centaurus |
| Right ascension | 14h 03m 49.40535s |
| Declination | –60° 22′ 22.9266″ |
| Apparent magnitude (V) | 0.61 |
| Astrometry | |
| Radial velocity (Rv) | +5.9 km/s |
| Proper motion (μ) |
RA: –33.27 mas/yr Dec.: –23.16 mas/yr |
| Parallax (π) | 8.32 ± 0.50mas |
| Distance | 390 ± 20 ly (120 ± 7 pc) |
| Absolute magnitude (MV) | −4.53 |
| Characteristics | |
| U−B color index | –0.98 |
| B−V color index | –0.23 |
| β Cen A1 | |
| Spectral type | B1 III |
| Variable type | β Cep |
| β Cen A2 | |
| Spectral type | B1 III |
| Variable type | β Cep |
| β Cen B | |
| Spectral type | B1V? |
| Orbit | |
| Primary | β Cen A1 |
| Companion | β Cen A2 |
| Period (P) | 356.94 days |
| Semi-major axis (a) | 0.0253" |
| Eccentricity (e) | 0.825 |
| Inclination (i) | 67.4° |
| Periastron epoch (T) | 2451600.08 |
|
Argument of periastron (ω) (secondary) |
62.2° |
|
Semi-amplitude (K1) (primary) |
57.4 km/s |
|
Semi-amplitude (K2) (secondary) |
72.3 km/s |
| Orbit | |
| Primary | β Cen A |
| Companion | β Cen B |
| Period (P) | 288.267 yr |
| Semi-major axis (a) | 0.870" |
| Details | |
| Luminosity | 41,700 L☉ |
| Age | 14.1 ± 0.6 Myr |
| β Cen A1 | |
| Mass | 10.7 ± 0.1 M☉ |
| Surface gravity (log g) | 3.5 ± 0.4 cgs |
| Temperature | 25,000 ± 2,000 K |
| β Cen A2 | |
| Mass | 10.3 ± 0.1 M☉ |
| Surface gravity (log g) | 3.5 ± 0.4 cgs |
| Temperature | 25,000 ± 2,000 K |
| β Cen B | |
| Mass | 4.61 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
Beta Centauri (β Centauri, abbreviated Beta Cen, β Cen), also named Hadar, is a triple star system in the southern constellation of Centaurus. The system's combined apparent visual magnitude of 0.61 makes it the second-brightest star in Centaurus and one of the brightest stars in the night sky. According to parallax measurements from the astrometric Hipparcos satellite, the distance to this system is about 390 ± 20 light-years (120 ± 6 parsecs).
Beta Centauri is well known in the Southern Hemisphere as the inner of the two "Pointers" to the asterism known as 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 at the bottom to effectively determine South.
β Centauri (Latinised to Beta Centauri) is the star's Bayer designation.
It bore the traditional names Hadar and Agena. Hadar comes from the Arabic حضار (the root's meaning is "to be present" or "on the ground" or "settled, civilized area"), while the name Agena may ultimately be derived from the Latin genua, meaning "knees". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN approved the name Hadar for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.
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