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Toliman

Alpha Centauri
Alpha, Beta and Proxima Centauri (1).jpg
α Centauri and β Centauri, with Proxima circled in red
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 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 1.227 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 0.865 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
Argument of periastron (ω)
(secondary)
231.65±0.076°
Other designations
Toliman, Bungula, 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: 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: the double star Alpha Centauri A (also named Rigil Kentaurus) and Alpha Centauri B together with a small and faint red dwarf, Alpha Centauri C (also named Proxima Centauri), that may be gravitationally bound to the other two. 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 about that between Pluto and the Sun to that between Saturn and the Sun.

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 15,000 astronomical units (0.24 ly; 0.07 pc), equivalent to 500 times the size of Neptune's orbit. Proxima Centauri b, an Earth-sized exoplanet in the habitable zone of Proxima Centauri, has been detected.


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