Cosmic Scale
Alpha Centauri B
Orange dwarf · 4.37 light-years
How big is Alpha Centauri B?
Alpha Centauri B is about 1,201,000 km across.
See Alpha Centauri B in 3D, at true scale
Alpha Centauri B is the slightly smaller, cooler partner in the closest star system to the Sun. Together with Alpha Centauri A it forms a bright pair that looks like a single star to the naked eye, with Proxima orbiting far out.
At a glance
| Diameter | 1,201,000 km |
|---|---|
| Mass | 1.81 × 10³⁰ kg |
| Diameter compared with Earth | 94.3 × Earth |
| Distance | 4.37 light-years |
| Surface | 5,260 K |
| Orbit | 80 years around its twin |
| Type | Orange dwarf |
Good to know
- The two stars swing between 11 and 36 times the Earth–Sun distance apart.
- Alpha Centauri is the third-brightest star in the night sky, but is only visible from below about 29° north.
- Breakthrough Starshot proposes firing gram-scale probes here with lasers, arriving in about 20 years.
- Next smaller: Epsilon Eridani · 1,023,000 km
- Next larger: The Sun · 1,391,000 km