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}} Capella is the brightest star in the constellation Auriga, the sixth brightest in the night sky and the third brightest in the northern celestial hemisphere, after Arcturus and Vega. Its name is derived from the diminutive of the Latin ''capra'' "goat", hence "little goat". Capella also bears the Bayer designation Alpha Aurigae (often abbreviated to α Aurigae, α Aur or Alpha Aur). Although it appears to be a single star to the naked eye, it is actually a star system of four stars in two binary pairs. The first pair consists of two bright, large type-G giant stars, both with a radius around 10 times that of the Sun and two and a half times its mass, in close orbit around each other. Designated Capella Aa and Capella Ab, these two stars have both exhausted their core hydrogen fuel and become giant stars, though it is unclear exactly what stage they are on the stellar evolutionary pathway. The second pair, around 10,000 astronomical units from the first, consists of two faint, small and relatively cool red dwarfs. They are designated Capella H and Capella L. The stars labelled Capella C through to G and I through to K are actually unrelated stars in the same visual field. The Capella system is relatively close, at only from Earth. ==Observational history== Professor William Wallace Campbell of the Lick Observatory announced that Capella was binary in 1899, based on spectroscopic observations—he noted on photographic plates taken from August 1896 to February 1897 that a second spectrum appeared superimposed over the first, and that there was a doppler shift to violet in September and October and to red in November and February—showing that the components were moving toward and away from the Earth (and hence orbiting each other). Almost simultaneously, British astronomer Hugh Newall had observed its composite spectrum with a four prism spectroscope attached to a 25-inch telescope at Cambridge in July 1899, concluding that it was a binary star system. Many observers tried to discern the component stars without success. Known as "The Interferometrist's Friend", it was first resolved interferometrically in 1919 by John Anderson and Francis Pease at Mount Wilson Observatory, who published an orbit in 1920 based on their observations. This was the first interferometric measurement of any object outside the Solar System.〔( Modern Optical Interferometry ), ''Astronomical Optical Interferometry: A Literature Review'', Bob Tubbs, St. John's College, Cambridge, April 1997. Accessed on line December 30, 2008.〕 A high-precision orbit was published in 1994 based on observations by the Mark III Stellar Interferometer, again at Mount Wilson Observatory.〔 Capella also became the first astronomical object to be imaged by a separate element optical interferometer when it was imaged by the Cambridge Optical Aperture Synthesis Telescope in September 1995.〔.〕 In 1914, Finnish astronomer Ragnar Furuhjelm observed that the spectroscopic binary mentioned above had a faint companion star, which, as its proper motion was similar to that of the spectroscopic binary, was probably physically bound to it. In February 1936, Carl L. Stearns observed that this companion appeared to be double itself;〔.〕 this was confirmed in September that year by Gerard Kuiper. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Capella」の詳細全文を読む スポンサード リンク
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