Alpha Centauri (Star)

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Alpha Centauri A
Spectral G2 V
Type Main Sequence
Multiple Trinary
Luminosity 1.519 LSol
Lum Rank 21st
Absolute magnitude +4.38
Mag Terra 0.01
Temperature 5,790° K
Mass 1.100 MSol
Radius 1.227 RSol
Companion Alpha Centauri B & Alpha Centauri C


Alpha Centauri B
Spectral K1 V
Type Main Sequence
Multiple Near Companion
Luminosity 0.50 LSol
Absolute magnitude +5.71
Mag Terra 1.33
Temperature 5,260° K
Mass 0.9 MSol
Radius 0.865 RSol


Alpha Centauri C (Proxima Centauri)
Spectral M5.5 Ve
Type Main Sequence
Multiple Far Companion
Luminosity 0.00005 LSol
Absolute magnitude +15.6
Mag Terra 11.05
Temperature 3,040° K
Mass 0.123 (= 129 MJ) MSol
Radius 0.141 RSol


Alpha Centauri (also called Rigil Kentaurus or Toliman) is a multiple star system consisting of a main binary pair (Alpha Centauri A and Alpha Centauri B) orbited by a third red dwarf far companion, Alpha Centauri C or "Proxima Centauri" lying at about 15,000AU (~0.2ly) distant from the Alpha Centauri AB main pair.

Description (Specifications)[edit]

Alpha Centauri A and B orbit about a common center with an orbital period of about 79.91 years. The distance between them varies from as close as 11.2AU at periastron to as far as 35.6AU at apastron due to the binary's orbital eccentricity of e = 0.518. Alpha Centauri AB lies at a distance of about 1.34pc from the Sol system.

  • Alpha Centauri A is a G2 V main-sequence star that is slightly larger and more luminous than Sol with a similar yellowish-white color. It has a mass of about 1.1 MSol and a radius of about 1.23 RSol, with a habitable zone lying at about 1.25AU.
  • Alpha Centauri B is slightly smaller and less luminous than Sol, and is a main-sequence star of spectral type K1 V, having a characteristic yellow-orange color. Alpha Centauri B has a mass of about 0.90 MSol and a radius of about 0.86 RSol, with a habitable zone ranging from 0.5 to 0.9 AU from the star. Although it has a lower luminosity than the A-component, Alpha Centauri B emits more energy in the X-ray band.

Proxima Centauri is of spectral class M5.5 Ve, giving it a typically pinkish-orange coloration and making it subject to flare activity. It is likely bound gravitationally to Alpha Centauri AB, and orbits with a period between 100,000 and 500,000 years. Proxima has a mass of about 0.123 M (or 129 MJ) and a radius of 0.141 RSol (= 1.5 RJ). It is at a slightly smaller distance of 1.29 pc (4.24 ly) from Sol, making it the closest star to the Sol star system. The separation of Proxima from Alpha Centauri AB is about 0.06 pc (0.2 ly), or 15,000AU. The habitable zone of Proxima Centauri lies at about 0.023–0.054AU from the star, and a world located here would have an orbital period of 3.6–14 days.

  • Because of its low mass, the interior of Proxima Centauri is completely convective, causing energy to be transferred to the exterior by the movement of plasma rather than through radiative transport. This convection means that the helium ash left over from the thermonuclear fusion of hydrogen does not accumulate at the core, but instead circulates throughout the star. Unlike Sol, which will only burn through about 10% of its total hydrogen supply before leaving the main sequence, Proxima Centauri will consume nearly all of its fuel before the fusion of hydrogen comes to an end, becoming smaller and hotter as the fuel is used up and turning into a "blue dwarf" as its end approaches. It will finally end its life as a white dwarf, without having passed through the red-giant phase.

In about the year 6000CE (IY1500), due to the proper motion of Alpha Centauri, the star will appear close enough to Beta Centauri (aka Hadar or Agena) from the vantage point of Terra to form an optical double star, though in fact the Beta Centauri system is far more distant from Sol than the Alpha Centauri system.

The entire Alpha Centauri system is rich in metal deposits. [1]


The Alpha Centauri star system is approximately 1.34pc from Terra, and is located in a Coretrailing/Trailing direction from Terra at bearing 315.7o Galactic Longitude and -00.7o South Galactic Latitude.

History & Background (Dossier)[edit]

Alpha Centauri A is the primary star of the world Prometheus/Sol (Solomani Rim 2027), one of Terra's earliest colonies.

References & Contributors (Sources)[edit]

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This article was copied or excerpted from the following copyrighted sources and used under license from Far Future Enterprises or by permission of the author.

  1. Citation Missing - GURPS Traveller: Interstellar Wars
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  • External Link: SIMBAD @ University of Strasbourg: [2]