Depth 17 · Triple star system

Alpha Centauri

Alpha Centauri is the closest star system to the Sun: a pair of Sun-like stars, A and B, with a small red dwarf, Proxima Centauri, circling far outside them. Because A and B are so similar to the Sun and so close to us, they are prime targets in the search for planets and life beyond the solar system.

Fact sheet

Type

Triple star system (G-type and K-type main-sequence stars plus a red dwarf)

Distance

About 4.3 light-years from the Sun (the A and B pair)

Size

Alpha Centauri A is about 1.2 times the Sun's radius and 1.08 times its mass; Alpha Centauri B is about 0.86 times the Sun's radius and 0.91 times its mass

Constellation

Centaurus

Position in the sky

Right ascension 14h 40m, declination −60° 50′

Seeing it from Earth

Easily seen with the naked eye as one bright star from the Southern Hemisphere and low northern latitudes; it never rises for most of the Northern Hemisphere, and splitting A from B needs a small telescope.

On the voyage

Depth 17, in the Nearby stars section of the route, between the Oort Cloud and Proxima Centauri b

Things to know

• The system has three stars: Alpha Centauri A is a G-type star a little heavier than the Sun, B is a slightly cooler K-type star a little lighter than the Sun, and Proxima Centauri is a small red dwarf. NASA
• Alpha Centauri A and B circle each other about once every 80 years, while Proxima orbits the pair from more than 10,000 times the Earth-Sun distance. NASA Chandra
• Proxima is currently the single closest star to the Sun, with the A and B pair a very close second. NASA Chandra
• In 2024 the James Webb Space Telescope spotted a possible Saturn-mass gas giant orbiting Alpha Centauri A, but follow-up looks in 2025 did not see it again, so it remains an unconfirmed candidate. ESA/Webb
• Alpha Centauri A ranks as the third-brightest star in the night sky, and the system lies so far south that it is seen mainly from the Southern Hemisphere. ESA/Webb

Sources

• NASA Goddard SVS – Alpha Centauri Stellar System
• Chandra X-ray Observatory – Alpha Centauri (2018)
• ESA/Webb – Webb finds new evidence for planet around closest solar twin (weic2515)
• Akeson et al. 2021, AJ – Precision millimeter astrometry of the Alpha Centauri AB system (arXiv)