Α Centauri
.jpg) α Centauri and β Centauri, with Proxima circled in red
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| Observation data Epoch J2000.0 Equinox J2000.0 |
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|---|---|
| Constellation | Centaurus |
| Alpha Centauri A | |
| Right ascension | 14h 39m 36.49400s |
| Declination | –60° 50′ 02.3737″ |
| Apparent magnitude (V) | +0.01 |
| Alpha Centauri B | |
| Right ascension | 14h 39m 35.06311s |
| Declination | –60° 50′ 15.0992″ |
| Apparent magnitude (V) | +1.33 |
| Characteristics | |
| A | |
| Spectral type | G2V |
| U−B colour index | +0.24 |
| B−V colour index | +0.71 |
| B | |
| Spectral type | K1V |
| U−B colour index | +0.68 |
| 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) | 754.81 ± 4.11mas |
| Distance | 4.37ly |
| 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) | 754.81 ± 4.11mas |
| Distance | 4.37ly |
| Absolute magnitude (MV) | 5.71 |
| Details | |
| Alpha Centauri A | |
| Mass | 1.100 M☉ |
| Radius | 1.2234±0.0053 R☉ |
| Luminosity | 1.519 L☉ |
| Surface gravity (log g) | 4.30 cgs |
| Temperature | 5,790 K |
| Metallicity [Fe/H] | 0.20 dex |
| Rotation | 22 days |
| Age | ≈4.4 Gyr |
| Alpha Centauri B | |
| Mass | 0.907 M☉ |
| Radius | 0.8632±0.0037 R☉ |
| Luminosity | 0.5002 L☉ |
| Surface gravity (log g) | 4.37 cgs |
| Temperature | 5,260 K |
| Metallicity | 0.23 |
| Rotation | 41 days |
| Age | ≈6.5 Gyr |
| Orbit | |
| Primary | A |
| Companion | B |
| Period (P) | 79.91±0.011 yr |
| Semi-major axis (a) | 17.57±0.022″ |
| Eccentricity (e) | 0.5179±0.00076 |
| Inclination (i) | 79.205±0.041° |
| Longitude of the node (Ω) | 204.85±0.084° |
| Periastron epoch (T) | 1875.66±0.012 |
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Argument of periastron (ω) (secondary) |
231.65±0.076° |
| Other designations | |
| α Cen A: Rigil Kentaurus, Rigil Kent, α1 Centauri, HR 5459, HD 128620, GCTP 3309.00, LHS 50, SAO 252838, HIP 71683 | |
| α Cen B: α2 Centauri, HR 5460, HD 128621, LHS 51, HIP 71681 | |
| Database references | |
| SIMBAD | AB |
| A | |
| B | |
| Exoplanet Archive | data |
| ARICNS | data |
| Extrasolar Planets Encyclopaedia |
data |
Alpha Centauri (α Centauri, abbreviated Alpha Cen, α Cen) is the closest star system to the Solar System, being 4.37 light-years (1.34 pc) from the Sun. It consists of three stars: Alpha Centauri A and Alpha Centauri B, which form the binary star Alpha Centauri AB (also named Rigil Kentaurus), and a small and faint red dwarf, Alpha Centauri C (also named Proxima Centauri), which is loosely gravitationally bound and orbiting the other two at a current distance of about 13,000 astronomical units (0.21 ly). To the unaided eye, the two main components appear as a single point of light with an apparent visual magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and is the third-brightest star in the night sky, outshone only by Sirius and Canopus.
Alpha Centauri A (α Cen A) has 1.1 times the mass and 1.519 times the luminosity of the Sun, while Alpha Centauri B (α Cen B) is smaller and cooler, at 0.907 times the Sun's mass and 0.445 times its visual luminosity. During the pair's 79.91-year orbit about a common centre, the distance between them varies from nearly that between Pluto and the Sun (35.6 AU) to that between Saturn and the Sun (11.2 AU).
Proxima Centauri (α Cen C) is at the slightly smaller distance of 4.24 light-years (1.30 pc) from the Sun, making it the closest star to the Sun, even though it is not visible to the naked eye. The separation of Proxima from Alpha Centauri AB is about 13,000 astronomical units (0.21 ly), equivalent to about 430 times the size of Neptune's orbit. Proxima Centauri b, an Earth-sized exoplanet in the habitable zone of Proxima Centauri, was discovered in 2016.
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