Alpha Centauri
What is Alpha Centauri?
Stars· Distance 4.37 ly · size 1.2× Sun (A). The star system nearest the Sun, 4.37 light-years away. Two Sun-like stars circle each other about every 80 years, and the small red dwarf Proxima lies far off to the side.
📍 Visible from where you are right now — computed in your browser
Distance and spectral type
Alpha Centauri is about 4 light-years away, a yellow main-sequence star (spectral type G2V), in the constellation Crux. Its apparent magnitude is -0.3, visible to the naked eye.
Stellar figures
| Distance | 4.37 ly — nearest star system |
|---|---|
| Magnitude | −0.27 combined, third brightest |
| Members | A (G2V), B (K1V), Proxima |
| Period | 79.9 yr |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Behind the name
The nearest star system (4.3 ly). Breakthrough Starshot aims to send tiny probes here.
Alpha Centauri A and B: an 80-year dance and the hunt for planets
Alpha Centauri A and B follow stretched, oval orbits and circle each other every 79.9 years. They were last at their closest in 1955 and will be again in 2035. Seen from Earth, the gap between them widens and narrows over about 80 years, between 2 and 22 arcseconds. When the gap is narrow, the two are hard to split in a small telescope.
Because the two stars swing close to each other, planets can only have stable orbits fairly near each star. In 2012 a planet was announced around B, but it was later judged to be noise in the data. In August 2024 the James Webb Space Telescope imaged a point of light about 2 AU from A that may be a planet; more observations are needed to confirm it.
The star in depth
Alpha Centauri, 4.37 light-years away, is the star system closest to the Sun. Even light takes more than four years to cross that gap, and at Voyager 1's speed the trip would take over 70,000 years. In the night sky its two main stars merge into a single point of magnitude −0.27, the third-brightest star in the sky.
At its heart are two stars, A and B. A is almost a twin of the Sun, with 1.1 times its mass and 1.5 times its brightness. B is a little smaller and has an orange tint. The two circle each other every 79.9 years, and the distance between them swings from 11 to 36 AU: about the Sun–Saturn distance at closest, and a bit more than the Sun–Neptune distance at farthest.
The third star, Proxima Centauri, is a small red dwarf about 13,000 AU from the pair. At 4.25 light-years, it is the nearest single star to the Sun. It has a planet, Proxima b, that orbits at a distance where liquid water might be possible on its surface.
Alpha Centauri lies so far south that it never rises from Europe or most of the United States. In the Sky view, switch the location to Sydney and look near the Southern Cross to see it shining brightly. In the southern hemisphere it and its neighbour Hadar are used as pointers to find the Southern Cross. The 3D neighbourhood view shows how far these stars really are from the Sun.
Frequently asked
- How far is Alpha Centauri from Earth?
- The distance of Alpha Centauri is 4.37 ly — nearest star system.
- How bright is Alpha Centauri (apparent magnitude)?
- The magnitude of Alpha Centauri is −0.27 combined, third brightest.
- How long is the orbital period of Alpha Centauri?
- The period of Alpha Centauri is 79.9 yr.
- Which constellation is Alpha Centauri in?
- Alpha Centauri lies in the constellation Crux.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.