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Alpha Centauri (アルファ・ケンタウリ)


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ケンタウルス座α星は、ケンタウルス座で最も明るい恒星で全天21の1等星の1つ。

特徴
恒星が3個ある三重連星である。太陽系から4.39光年しか離れておらず、最も近い恒星系でもある。
太陽系に近付いており、およそ25,000年後には3光年まで接近する。

主星(A星)は太陽に似た黄色の主系列星で、スペクトル型は太陽と同じG2V。
太陽よりも少し明るい(太陽の絶対等級は4.85等)。


第1伴星(B星)は橙色の主系列星。B星はA星よりも強いX線を放射している。
第2伴星(C星)はプロキシマという名称で知られており、地球からの距離は4.22光年。
プロキシマの意味は、ラテン語で「最も近い」という意味であり、太陽系に最も近い恒星であることから来ている。
プロキシマはA/Bのペアから13,000AU(0.2光年)も離れており、公転周期は100万年にも及ぶ。

太陽からA・Bの共通重心までの距離は、それぞれの星までの距離とほとんど変わらない。

Alpha Centauri is a star located 4.3 light years from the Earth in the constellation Centaurus.

Alpha Centauri (アルファ・ケンタウリ) : Picture

Alpha Centauri
In the Glare of Alpha Centauri
(C) Marco Lorenzi (Glittering Lights)
The glare of Alpha Centauri, one of the brightest stars in planet Earth's night sky, floods the left side of this southern skyscape. A mere 4.3 light-years distant, Alpha Centauri actually consists of two component stars similar in size to the Sun, locked in a mutual orbit. Much smaller and cooler, a third member of the same star system, Proxima Centauri, lies outside this field of view. Still, the telescopic scene does reveal often overlooked denizens of the Milky Way's crowded galactic plane that lie beyond the glare of Alpha Centauri, including a planetary nebula cataloged as Hen 2-111, an estimated 7,800 light-years away. The gaseous shroud of a dying star, the nebula's brighter core and fainter halo of reddish ionized gas span over twenty light-years, seen just right of picture center. Farther right are two notable open clusters of stars, the compact Pismis 19 also nearly 8,000 light-years away whose light is reddened by intervening dust, and the looser, closer NGC 5617. Just visible in the glare of Alpha Centauri is the dim glow of a shell-like supernova remnant, above and right of the closest star system's bright core.

Alpha Centauri: The Closest Star System
Alpha Centauri: The Closest Star System
(C) STSci Digitized Sky Survey, Anglo-Australian Observatory
The closest star system to the Sun is the Alpha Centauri system. Of the three stars in the system, the dimmest -- called Proxima Centauri -- is actually the nearest star. The bright stars Alpha Centauri A and B form a close binary as they are separated by only 23 times the Earth- Sun distance - slightly greater than the distance between Uranus and the Sun. In the above picture, the brightness of the stars overwhelm the photograph causing an illusion of great size, even though the stars are really just small points of light. The Alpha Centauri system is not visible in much of the northern hemisphere. Alpha Centauri A, also known as Rigil Kentaurus, is the brightest star in the constellation of Centaurus and is the fourth brightest star in the night sky. Sirius is the brightest even thought it is more than twice as far away. By an exciting coincidence, Alpha Centauri A is the same type of star as our Sun, causing many to speculate that it might contain planets that harbor life.

Alpha Centauri: The Closest Star System
Alpha Centauri: The Closest Star System
(C) 1-Meter Schmidt Telescope, ESO
The closest star system to the Sun is the Alpha Centauri system. Of the three stars in the system, the dimmest -- called Proxima Centauri -- is actually the nearest star. The bright stars Alpha Centauri A and B form a close binary as they are separated by only 23 times the Earth- Sun distance - slightly greater than the distance between Uranus and the Sun. In the above picture, the brightness of the stars overwhelm the photograph causing an illusion of great size, even though the stars are really just small points of light. The Alpha Centauri system is not visible in much of the northern hemisphere. Alpha Centauri A, also known as Rigil Kentaurus, is the brightest star in the constellation of Centaurus and is the fourth brightest star in the night sky. Sirius is the brightest even thought it is more than twice as far away. By an exciting coincidence, Alpha Centauri A is the same type of star as our Sun, causing many to speculate that it might contain planets that harbor life.

Interstellar Distances - In Perspective
Interstellar Distances - In Perspective
(C) NASA
The Voyager spacecraft left the solar system at 37,000 miles per hour. At that speed, it would take Voyager 80,000 years to reach Proxima Centauri.

Alpha Centauri System
A comparison of the sizes and colors of the stars in the Alpha Centauri system with the Sun.
(C) David Benbennick

Position Alpha Centauri
Position Alpha Centauri

Alpha Centauri Alpha Centauri
In the Glare of Alpha Centauri
(C) Marco Lorenzi (Glittering Lights)
Alpha Centauri: The Closest Star System
(C) STSci Digitized Sky Survey, Anglo-Australian Observatory
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Alpha Centauri (アルファ・ケンタウリ) : Movie

A journey to Alpha Centauri
This video shows an imaginary journey from Earth to the Alpha Centauri system. As we leave the Solar System we see the familiar constellation figures including the Southern Cross (Crux) and the bright stars Alpha and Beta Centauri. As we approach Alpha Centauri we pass a faint red star, this is Proxima Centauri, the closest star to Earth and the faintest component of a triple star system. The final part shows the bright double star Alpha Centauri A and B with the Sun visible in the background. Alpha Centauri B is known to be orbited by an Earth-mass planet, the closest exoplanet to the Solar System.

A fly-through of the Alpha Centauri system
This video shows a fly-through of the bright double star Alpha Centauri A and B. In the final sequence we close in on Alpha Centauri B and a newly discovered planet swims into view. This Earth-mass planet is the closest exoplanet known and the lightest ever found around a star like the Sun.
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「ウィキペディア(wikipedia):フリー百科事典」より文章引用。
ケンタウルス座アルファ星. (2013, November 10). In Wikipedia.
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