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Kinematics

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All components of Alpha Centauri display significant proper motion against the background sky. Over centuries, this causes their apparent positions to slowly change. Proper motion was unknown to ancient astronomers. Most assumed that the stars are permanently fixed on the celestial sphere, as stated in the works of the philosopher Aristotle. In 1718, Edmond Halley found that some stars had significantly moved from their ancient astrometric positions. In the 1830s, Thomas Henderson discovered the true distance to Alpha Centauri by analysing his many astrometric mural circle observations. He then realised this system also likely had a high proper motion. In this case, the apparent stellar motion was found using Nicolas Louis de Lacaille's astrometric observations of 1751–1752, by the observed differences between the two measured positions in different epochs. Calculated proper motion of the centre of mass for Alpha Centauri AB is about 3620 mas (milli-arcseconds) per year toward the ...
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Nomenclature

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α Centauri (Latinised to Alpha Centauri ) is the system's designation given by Johann Bayer in 1603. It bears the traditional name Rigil Kentaurus , which is a Latinisation of the Arabic name رِجْل القِنْطورُس ‎ Rijl al-Qinṭūrus, meaning 'the Foot of the Centaur'. The name is frequently abbreviated to Rigil Kent or even Rigil , though the latter name is better known for Beta Orionis (Rigel). An alternative name found in European sources, Toliman , is an approximation of the Arabic الظَّلِيمَان ‎ aẓ-Ẓalīmān (in older transcription, aṭ-Ṭhalīmān ), meaning 'the (two male) Ostriches', an appellation Zakariya al-Qazwini had applied to Lambda and Mu Sagittarii, also in the southern hemisphere. A third name that has been applied is Bungula ( / ˈ b ʌ ŋ ɡ juː l ə / ), of obscure origin. Allen can only surmise it may have been coined from the Greek letter beta (β) and Latin ungula 'hoof'. Alpha Centauri C was discovered in 1915 by Robert T. A. Innes, who suggest...
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Stellar system

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Alpha Centauri is a triple star system, with its two main stars, Alpha Centauri A and Alpha Centauri B, being a binary component. The AB designation, or older A×B , denotes the mass centre of a main binary system relative to companion star(s) in a multiple star system. AB-C refers to the component of Proxima Centauri in relation to the central binary, being the distance between the centre of mass and the outlying companion. Because the distance between Proxima (C) and either of Alpha Centauri A or B is similar, the AB binary system is sometimes treated as a single gravitational object. Orbital properties edit The A and B components of Alpha Centauri have an orbital period of 79.91 years. Their orbit is moderately eccentric, e  = 0.5179; their closest approach or periastron is 11.2 AU (1.68 billion km), or about the distance between the Sun and Saturn; and their furthest separation or apastron is 35.6 AU (5.33 billion km), about the distance between the Sun and Pluto. The most recent ...
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