Alpha Centauri
Alpha Centauri AB (left) forms a triple star system with Proxima Centauri (below, south of, α Centauri AB). (See labelled version) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Centaurus |
| α Centauri A (Rigil Kentaurus) | |
| Right ascension | 14h 39m 36.49400s |
| Declination | −60° 50′ 02.3737″ |
| Apparent magnitude (V) | +0.01 |
| α Centauri B (Toliman) | |
| Right ascension | 14h 39m 35.06311s |
| Declination | −60° 50′ 15.0992″ |
| Apparent magnitude (V) | +1.33 |
| Characteristics | |
| A | |
| Spectral type | G2V |
| B−V colour index | +0.71 |
| B | |
| Spectral type | K1V |
| B−V colour index | +0.88 |
| Astrometry | |
| A | |
| Radial velocity (Rv) | −21.4±0.76 km/s |
| Proper motion (μ) | RA: −3679.25 mas/yr Dec.: +473.67 mas/yr |
| Parallax (π) | 750.81±0.38 mas |
| Distance | 4.344 ± 0.002 ly (1.3319 ± 0.0007 pc) |
| Absolute magnitude (MV) | 4.38 |
| B | |
| Radial velocity (Rv) | −18.6±1.64 km/s |
| Proper motion (μ) | RA: −3614.39 mas/yr Dec.: +802.98 mas/yr |
| Parallax (π) | 750.81±0.38 mas |
| Distance | 4.344 ± 0.002 ly (1.3319 ± 0.0007 pc) |
| Absolute magnitude (MV) | 5.71 |
| Orbit | |
| Primary | A |
| Name | B |
| Period (P) | 79.762±0.019 yr |
| Semi-major axis (a) | 17.493±0.0096" (23.299 AU) |
| Eccentricity (e) | 0.51947±0.00015 |
| Inclination (i) | 79.243±0.0089° |
| Longitude of the node (Ω) | 205.073±0.025° |
| Periastron epoch (T) | 1875.66±0.012 |
| Argument of periastron (ω) (secondary) | 231.519±0.027° |
| Details | |
| α Centauri A | |
| Mass | 1.0788±0.0029 M☉ |
| Radius | 1.2175±0.0055 R☉ |
| Luminosity | 1.5059±0.0019 L☉ |
| Surface gravity (log g) | 4.30 cgs |
| Temperature | 5,804±13 K |
| Metallicity [Fe/H] | 0.20±0.01 dex |
| Rotation | 28.3±0.5 d |
| Rotational velocity (v sin i) | 2.7±0.7 km/s |
| Age | 7.2–7.8 Gyr |
| α Centauri B | |
| Mass | 0.9092±0.0025 M☉ |
| Radius | 0.8591±0.0036 R☉ |
| Luminosity | 0.4981±0.0007 L☉ |
| Surface gravity (log g) | 4.37 cgs |
| Temperature | 5,207±12 K |
| Metallicity [Fe/H] | 0.24±0.01 dex |
| Rotation | 36.7±0.3 d |
| Rotational velocity (v sin i) | 1.1±0.8 km/s |
| Age | 7.2–7.8 Gyr |
| Other designations | |
| α Cen, CD−60°5293, CPD−60°5483, FK5 538, GC 19728, GJ 559, SAO 252838, CCDM J14396-6050 | |
| α Cen A: Rigil Kentaurus, Rigil Kent, α1 Cen, HD 128620, HIP 71683, HR 5459, LHS 50, PLX 3309 | |
| α Cen B: Toliman, α2 Cen, HD 128621, HIP 71681, HR 5460, LHS 51 | |
| Database references | |
| SIMBAD | AB |
| A | |
| B | |
| Exoplanet Archive | data |
| ARICNS | data |
Alpha Centauri (α Centauri, α Cen, or Alpha Cen) is a star system in the southern constellation of Centaurus. It consists of three stars: Rigil Kentaurus (α Centauri A), Toliman (α Centauri B), and Proxima Centauri (α Centauri C). Proxima Centauri is the closest star to the Sun at 4.2465 light-years (ly), which is 1.3020 parsecs (pc), while Alpha Centauri A and B are the nearest stars visible to the naked eye.
Rigil Kentaurus and Toliman are Sun-like stars (class G and K, respectively) that together form the binary star system α Centauri AB. To the naked eye, these two main components appear to be a single star with an apparent magnitude of −0.27. It is the brightest star in the constellation and the third-brightest in the night sky, outshone by only Sirius and Canopus. α Centauri AB are the nearest binary stars to the Sun at a distance of 4.344 ly (1.33 pc).
Rigil Kentaurus has 1.1 times the mass (M☉) and 1.5 times the luminosity of the Sun (L☉), while Toliman is smaller and cooler, at 0.9 M☉ and less than 0.5 L☉. The pair orbit around a common centre with an orbital period of 79 years. Their elliptical orbit is eccentric, so that the distance between A and B varies from 35.6 astronomical units (AU), or about the distance between Pluto and the Sun, to 11.2 AU, or about the distance between Saturn and the Sun.
Proxima Centauri is a small faint red dwarf (class M). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of 4.24 ly (1.30 pc), slightly closer than α Centauri AB. The distance between Proxima Centauri and α Centauri AB is about 13,000 AU (0.21 ly), equivalent to about 430 times the radius of Neptune's orbit.
Proxima Centauri has two confirmed planets — Proxima b and Proxima d. The former is an Earth-sized planet in the habitable zone (though it is unlikely to be habitable) while the latter is a sub-Earth which orbits very closely to the star. A possible but disputed third planet, Proxima c, is a mini-Neptune 1.5 astronomical units away. Rigil Kentaurus may have a Saturn-mass planet (Alpha Centauri Ab) in the habitable zone, though it is not yet known with certainty to be planetary in nature. Toliman has no known planets.