Alpha Centauri
- Alternative meaning: Alpha Centauri computer game
Alpha Centauri is the brightest star system in the southern constellation of Centaurus, and is the third brightest in the entire night sky (although too far south to be visible in most of the northern hemisphere).
It is also the closest star system to Earth, at 4.2-4.4 light-years. That makes it a logical choice as "first port of call" for science fiction and computer game speculation about space travel.
Names
It bears the proper name Rigil Kentaurus (often shortened to Rigil Kent), derived from the Arabic phrase for "foot of the centaur," but is nonetheless usually referred to by its Bayer designation Alpha Centauri. Another alternative name is Toliman. It and the nearby Beta Centauri are the "Pointers" to the Southern Cross.
System components
Relative size of stars in Alpha Centauri system, and our Sun
Alpha Centauri is a triple star system. It consists of two main stars, Alpha Centauri A and Alpha Centauri B (which form a binary star together) at a distance of 4.36 ly, and a dimmer red dwarf named Proxima Centauri at a distance of 4.22 ly. The larger member of the binary star, Alpha Centauri A, is similar to the Sun, but a little larger and brighter. Like the sun, its spectral type is G2 V. The smaller of the two, Alpha Centauri B, is dimmer, with a spectral type of K1 V. The two orbit one another elliptically (e=0.52), approaching as close as 11.2 astronomical units (0.000,2 ly) and receding to 35.6 AU (0.000,6 ly)with a period of just under 80 years. Hence the sum of the two masses is <math>23.4^3/80^2=2.0<math> times that of the Sun (see formula).
These two stars are about 5 to 6 billion years old.
The red dwarf Proxima Centauri is about 13,000 astronomical units away from Alpha Centauri (1 ly = 63,241 AU, hence this is 0.2 ly, about 1/20 of the distance between Alpha Centauri and the Sun, it is 0.14 ly closer to us) 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.
Seen from Earth, Proxima is separated by 2 degrees from Alpha Centauri A and B (about 4 times the angular diameter of the full Moon), and the latter are at an angular distance of up to 40" from each other.
Possibility of planet formation
Computer models of planetary formation suggest that terrestrial planets would be able to form close to both Alpha Centauri A and B, but that gas giant planets similar to our Jupiter and Saturn would not be able to form because of the binary stars' gravitational effects. Given the similarities in star type, age and stability of the orbits it has been suggested that this solar system may hold one of the best possibilities for extraterrestrial life. However, some astronomers have speculated that any terrestrial planets in the Alpha Centauri system may be dry because it is believed that Jupiter and Saturn were crucial at directing comets into the inner solar system and providing the inner planets with a source of water.
Sky appearance from Alpha Centauri
Viewed from Alpha Centauri, the sky would appear very much as it does to us with most of the constellations such as Ursa Major and Orion being unchanged. However, Centaurus would be missing its brightest star and Cassiopeia would be home to a bright star in the form of Sol, our Sun. Nearby very bright stars such as Sirius and Procyon would be in very different positions, as would Altair to a lesser extent. Fomalhaut and Vega would appear somewhat displaced as well.
Apparent movement
In about 4000 years, the proper motion of Alpha Centauri will mean that from the point of view of Earth it will appear close enough to Beta Centauri to form an optical double star. Beta Centauri is in reality far more distant than Alpha Centauri.
See also
External links
- Alpha Centauri (http://www.glyphweb.com/esky/stars/alphacentauri.html)
- Alpha Centauri: A Candidate for Terrestrial Planets And Intelligent Life (http://homepage.sunrise.ch/homepage/schatzer/Alpha-Centauri.html)
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