NOTE: View in monospaced font June 9, 1991 ALPHCENT.TXT ALPHA CENTAURI SYSTEM MODIFIED FROM EARLIER CONTACT: The Alpha Centauri system is 4.3 light years from Earth at right ascension 14 hours 36.2 minutes and declination -60 degrees 38 minutes (60.63 degrees south of Earth's equator). It consists of three stars: Alpha Centauri A, B, and C; the latter is also called Proxima Centauri because it is the star closest to Sol, at 4.3 light years. Its right ascension is 14 hours 26.3 minutes and declination -62 degrees 28 minutes. The other two stars are about 4.4 light years from Sol. Alpha Centauri A is a yellow (G2) star similar to Sol, but 10% more massive and 25% more luminous. Alpha Centauri B is orange (K6) and is therefore cooler than Sol; it has 87% the mass of Sol, but is only 37% as luminous. Alpha Centauri C is a red dwarf (M5) with about 10% the mass and luminosity of Sol. This normally cool star flares a few times per week, and the blue-white flare increases the star's brightness by a factor of 100 within a few seconds and then declines in about an hour. Alpha Centauri A and B orbit each other in about 80 years in an eccentric ellipse with semimajor axis 23.4 AU. The come as close as 11.2 AU and as far as 35.6 AU. Alpha Centauri C orbits the other two stars once in more than 300,000 years at a distance of more than 1/6 light year. Lang's Astrophysical Formulae (1980) page 528-9 list the following data for Sol and the Alpha Centauri system: r.a. decl. proper pos. abs. spect. (1950.0) (1950.0) motion ang, vis. type mag. lum. hr min deg min deg Sol 4.8 G2 1.0 A 14 36.2 -60 38 3.6" 281 4.5 G2 1.3 B 5.9 K6 0.36 C 14 26.3 -62 28' 3.84" 282 15.4 M5e 0.00006 (C = Proxima, 2 degrees 11' from center of mass of A & B) A planet that orbits Alpha Centauri A in a circular orbit with radious 1.1 AU will have almost the same insolation as Earth. The direct effect of Alpha Centauri B on the planet is insignificant. Even at closest approach (10.1 AU), the contribution of radiation from Alpha Centauri B is only an additional 0.4%. The tidal force from Alpha Centauri A on the planet is 0.83 times the solar tidal force on Earth. At closest approach the tidal force from Alpha Centauri B on the planet is only 0.00085 times the solar tidal force on Earth. However, the indirect effect of Alpha Centauri B on the planet may be profound by perturbing the orbit of the planet about Alpha Centaui A.