Science Fair Project Encyclopedia
Proxima Centauri was discovered in 1915 by Robert Innes while he was Director of the Union Observatory in Johannesburg, South Africa. It is also known as Alpha Centauri C, V645 Centauri, Gl 551, LHS 49, and GCTP 3278.00.
Based on the parallax of 772.33 ± 2.42 milliarcsec measured by Hipparcos, Proxima Centauri is roughly 4.22 light years from Earth (39.9 Pm), or 270,000 times more distant than the Sun. Its closest neighbours are Alpha Centauri A and B (0.06 pc or 0.21 ly), the Sun, and Barnard's Star (2.01 pc or 6.55 ly).
In 2002, VLTI used optical interferometry to measure the angular diameter of Proxima Centauri as 1.02 ± 0.08 milliarcsec. Knowing its distance, the actual diameter can be determined to be about 1/7 that of the Sun, or 1.5 times that of Jupiter. The mass is also about 1/7 that of the Sun, or 150 times that of Jupiter.
Its apparent magnitude is 11 and its absolute magnitude 15.53 (very weak, as red dwarfs in general are far too weak to be observable with the naked eye). As seen from Alpha Centauri A and B, Proxima is a 4.5 magnitude star.
Proxima Centauri is about 13,000 astronomical units away from Alpha Centauri (this is about 2 Pm, or 0.2 light years, or about 1/20 of the distance between Alpha Centauri and the Sun) and may be in orbit about it, with a period on the order of 500,000 years or more. For this reason, Proxima is sometimes referred to as Alpha Centauri C. However, it is not clear if it really is in orbit, although the association is unlikely to be entirely accidental as it shares approximately the same motion through space as the larger star system. From Earth's vantage point Proxima is separated by 2 degrees from Alpha Centauri (about 4 times the angular diameter of the full Moon).
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