Alpha Centauri

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Related to Alpha Centauri system: Proxima Centauri, Milky Way System

Alpha Centauri

(ăl`fə sĕntôr`ē), brightest star in the constellation CentaurusCentaurus
, southern constellation located N and E of Crux, the Southern Cross. It is known especially for its bright stars Alpha Centauri and Hadar. It also contains Centaurus A, a radio galaxy, as well as a globular star cluster visible to the naked eye.
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 and 3d-brightest star in the sky; also known as Rigil Kent or Rigil Kentaurus; 1992 position R.A. 14h39.1m, Dec. −60°49'. Its apparent magnitudemagnitude,
in astronomy, measure of the brightness of a star or other celestial object. The stars cataloged by Ptolemy (2d cent. A.D.), all visible with the unaided eye, were ranked on a brightness scale such that the brightest stars were of 1st magnitude and the dimmest stars
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 is −0.26. Alpha Centauri is actually a triple-star system, the components being designated A, B, and C. Alpha Centauri A is the brightest component; it is a yellow main-sequence star of the same spectral classspectral class,
in astronomy, a classification of the stars by their spectrum and luminosity. In 1885, E. C. Pickering began the first extensive attempt to classify the stars spectroscopically.
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 (G2 V) as the sun and of about the same size and mass. It forms a binary system with the somewhat smaller, less bright, and more orange Alpha Centauri B. Alpha Centauri C, a red dwarf, is also called Proxima Centauri because it is the closest star to the earth (other than the sun), at a distance of 4.28 light-years; components A and B are currently 4.34 light-years away. Proxima Centauri orbits about the common center of mass of the system with a period of more than 250,000 years, so that in about 125,000 years it will be more distant than A and B. In 2012 the discovery of a roughly earth-sized planet orbiting Alpha Centauri B was announced; the planet was reported to orbit the star closer than Mercury orbits the sun. A roughly earth-sized planet has also been identified (2016) orbiting Proxima Centauri. Though it orbits its star much more closely than the Mercury does the sun, it is believed to be in the habitable zone because of the cooler temperatures of Proxima Centauri; however, the star is of a type that tends to produce solar flares readily, which would bombard the nearby planet with high levels of radiation and strip any atmosphere from it.

Alpha Centauri

(sen-tor -ÿ, -ee) (Rigil Kentaurus; α Cen) A binary star that is the brightest star in the constellation Centaurus, one of the brightest in the sky, and the second nearest star to the Sun. The two components, A and B, form a yellow-orange visual binary (separation 17″.7, period 80.1 years) and are similar in mass and size to the Sun. Proxima Centauri appears to be physically associated with α Cen; it is the nearest star to the Sun. mv : –0.01 (A), 1.33 (B), –0.27 (AB); Mv : 4.4 (A), 5.7 (B), 4.1 (AB); spectral type: G2 V (A), K1 V (B); mass: 1.09 (A), 0.89 (B) times solar mass; distance: 1.33 pc.

Alpha Centauri

[¦al·fə sen′tȯ·rē]
(astronomy)
A double star, the brightest in the constellation Centaurus; apart from the sun, it is the nearest bright star to earth, about 4.3 light-years away; spectral classification G2. Also known as Rigil Kent.

Alpha Centauri

brightest star in Centaurus constellation; closest star to Earth. [Astronomy: NCE, 74]
References in periodicals archive ?
For the Breakthrough Iniative's Starshot program, which has an audacious aim of sending tiny robotic probes to not only visit, but also to return from a trip to the Alpha Centauri system within a generation, knowing the location of any potential exoplanets in the system is crucial.
In this issue, there are a number of discoveries that the Nobel committee might want to ponder: news of a new planet found just 4.4 light-years from Earth in the Alpha Centauri system (Page 5); the latest on the long-overlooked primary cilia and their surprising role in a variety of diseases (Page 16); the discovery of quasicrystals in an obscure meteorite shard (Page 24); and degradable electronics (Page 15).--Eva Emerson, Acting Editor in Chief
Even more famous is Barnard's Star, the closest star beyond the three members of the Alpha Centauri system. Barnard's Star lies just 5.94 light-years from Earth.
Proper-motion studies in 1915 identified a nearby 11th-magnitude star as part of the Alpha Centauri system. This star's distance was measured as 4.2 light-years in 1917, making it the closest star to our solar system and leading to its designation as Proxima Centauri.
All the above dates refer to the Alpha Centauri system as we see it.
Now, how far away would the Alpha Centauri system be from this yardstick solar system?
The next-closest star after the Alpha Centauri system is Barnard's Star in northeast Ophiuchus; it's still very low in the east.
Wiegert stresses, "These results are purely theoretical; no planets have been detected in the Alpha Centauri system to date." But the scientists hope that calculations like theirs may tell 21st-century astronomers where to focus their attempts to detect Earth-like worlds.
This distance is only three times that of the Alpha Centauri system. (GJ 1061 is not the 20th-nearest star, however, because several of the entries further up the list are binary or triple star systems.)