Alpha Centauri A

Alpha Centauri A

Star

Alpha Centauri A (Rigil Kentaurus) — a Sun-like G2V star, the brighter member of the closest star system to the Sun, 4.37 light-years away. It circles a shared center of mass with Alpha Centauri B every 79.8 years, swinging between 11.2 and 35.6 AU from its companion.

Open in 3D viewSee Alpha Centauri A in the live, interactive 3D map

Key facts

Mutual orbit
79.8 Earth years
29,133 Earth days
Mass
2.15 × 10³⁰ kg
1.08 M☉
Radius
847,015 km
1.22× wider than the Sun
Surface temperature
5,804 K (5531 °C)
Spectral type
G2V (yellow dwarf — the same class as the Sun)

Science

Physical

Mass
2.15 × 10³⁰ kg · 1.08 M☉
Radius
847,015 km · 1.22× wider than the Sun
Density
843 kg/m³ · 0.84× water
Spectral type
G2V (yellow dwarf — the same class as the Sun)

Orbit (around the system barycenter)

Semi-major axis
10.7 AU
Eccentricity
0.5195
Orbital period
79.76 years

Rotation

Equatorial period
22.0 days
Note
Rotation ≈ 22 days, inferred from chromospheric activity

Composition

By mass
A near solar-twin by spectroscopy: hydrogen and helium with slightly higher metal content than the Sun (~1.7× solar metallicity)

Temperature

Surface
5,804 K (5531 °C)

Radiation & temperature

Luminosity
5.76 × 10²⁶ W · 1.51 L☉
Surface temperature
5,804 K (5531 °C)
Peak wavelength
499 nm · green-yellow visible light

Discovery & history

Method
Naked-eye star
Name
Rigil Kentaurus — the IAU proper name, from the Arabic Rijl al-Qanṭūris, 'the foot of the Centaur'. 'Alpha Centauri' marks it as the brightest star of the constellation Centaurus (Bayer designation, 1603).

Alpha Centauri has been known since antiquity as the brightest star of Centaurus. In December 1689 the Jesuit astronomer Jean Richaud, observing a comet from Puducherry, India, discovered it is actually TWO stars — one of the first binary stars ever resolved. Between 1832 and 1833 Thomas Henderson measured its parallax from the Cape of Good Hope; published in 1839, it was among the first stellar distances ever determined, revealing the system as our nearest stellar neighbour.

Images

Alpha Centauri A (left) and B — the closest star system, resolved by Hubble
ESA/Hubble & NASA (CC BY 4.0) · Wikimedia Commons
The Alpha Centauri pair seen three ways: Digitized Sky Survey, Hubble, and JWST
NASA, ESA, CSA, STScI, DSS, A. Sanghi (Caltech), C. Beichman (CC BY 4.0) · Wikimedia Commons
Alpha Centauri blazing over ESO's Paranal Observatory, Chile
John Colosimo / ESO (CC BY 4.0) · Wikimedia Commons

Images from open archives · credit shown per image