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Alpha Centauri AB
Alpha, Beta and Proxima Centauri (1).jpg
α Centauri AB is the bright star to the left, with Proxima Centauri circled in red. The bright star to the right is β Centauri.
Observation data
Epoch J2000.0      Equinox J2000.0
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 color index +0.24
B−V color index +0.71
B
Spectral type K1V
U−B color index +0.68
B−V color 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 ± 4.11 mas
Distance4.37 ly
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 ± 4.11 mas
Distance4.37 ly
Absolute magnitude (MV)5.71
Details
Alpha Centauri A
Mass1.100 M
Radius1.2234±0.0053 R
Luminosity1.519 L
Surface gravity (log g)4.30 cgs
Temperature5,790 K
Metallicity [Fe/H]0.20 dex
Rotation22±5.9 d
Rotational velocity (v sin i)2.7±0.7 km/s
Alpha Centauri B
Mass0.907 M
Radius0.8632±0.0037 R
Luminosity0.5002 L
Surface gravity (log g)4.37 cgs
Temperature5,260 K
Metallicity0.23
Rotation36 days
Rotational velocity (v sin i)1.1±0.8 km/s
Age5.3±0.3 Gyr
Orbit
PrimaryA
CompanionB
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
Argument of periastron (ω)
(secondary)
231.65±0.076°
Other designations
Gliese 559, FK5 538, CD−60°5483, CCDM J14396-6050, GC 19728
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: Toliman, α2 Centauri, HR 5460, HD 128621, LHS 51, HIP 71681
Database references
SIMBADAB

A

B
Exoplanet Archivedata
ARICNSdata
Extrasolar Planets
Encyclopaedia
data

Alpha Centauri is the closest star system and closest planetary system to the Solar System at 4.37 light-years (1.34 pc) from the Sun. It is a triple star system, consisting of three stars: α Centauri A (officially Rigil Kentaurus), α Centauri B (officially Toliman), and α Centauri C (officially Proxima Centauri).

Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.

Alpha Centauri A has 1.1 times the mass and 1.519 times the luminosity of the Sun, while Alpha Centauri B is smaller and cooler, at 0.907 times the Sun's mass and 0.445 times its luminosity. The pair orbit about a common center with an orbital period of 79.91 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 that between Saturn and the Sun (11.2 AU).

Alpha Centauri C, or Proxima Centauri, is a small and 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 light-years (1.30 pc), slightly closer than Alpha Centauri AB. Currently, the distance between Proxima Centauri and Alpha Centauri AB is about 13,000 astronomical units (0.21 ly), equivalent to about 430 times the radius of Neptune's orbit. Proxima Centauri b is an Earth-sized exoplanet in the habitable zone of Proxima Centauri; it was discovered in 2016.

Nomenclature