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Proxima Centauri (Latin ラテン語:''proxima'', meaning "next to" or "nearest to")〔(【引用サイトリンク】 title=Latin Resources )〕 is a red dwarf about 4.24 light-years from the Sun, inside the G-cloud, in the constellation of Centaurus. It was discovered in 1915 by the Scottish astronomer Robert Innes, the Director of the Union Observatory in South Africa, and is the nearest known star to the Sun, although it is too faint to be seen with the naked eye, with an apparent magnitude of 11.05. Its distance to the second- and third-nearest stars, which form the bright binary Alpha Centauri, is 0.237 ± 0.011 ly (15,000 ± 700 AU). Proxima Centauri is very likely part of a triple star system with Alpha Centauri A and B, but its orbital period may be greater than 500,000 years. Because of Proxima Centauri's proximity, its distance from Earth and angular diameter can be measured directly, from which it can be determined that its diameter is about one-seventh of that of the Sun.〔 Proxima Centauri's mass is about an eighth of the Sun's (), and its average density is about 40 times that of the Sun.〔 Although it has a very low average luminosity, Proxima is a flare star that undergoes random dramatic increases in brightness because of magnetic activity. The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun.〔 The mixing of the fuel at Proxima Centauri's core through convection and its relatively low energy-production rate mean that it will be a main-sequence star for another four trillion years,〔 or nearly 300 times the current age of the universe. Searches for companions orbiting Proxima Centauri have been unsuccessful, ruling out the presence of brown dwarfs and supermassive planets.〔〔 Precision radial velocity surveys have also ruled out the presence of super-Earths within the star's habitable zone.〔This is actually an upper limit on the quantity ''m'' sin ''i'', where ''i'' is the angle between the orbit normal and the line of sight, in a circular orbit. If the planetary orbits are close to face-on as observed from Earth, or in an eccentric orbit, more massive planets could have evaded detection by the radial velocity method.〕 The detection of smaller objects will require the use of new instruments, such as the James Webb Space Telescope, which is scheduled for deployment in 2018.〔 Because Proxima Centauri is a red dwarf and a flare star, whether a planet orbiting it could support life is disputed. Nevertheless, because of the star's proximity to Earth, it has been proposed as a destination for interstellar travel. ==Observation== In 1915, the Scottish astronomer Robert Innes, Director of the Union Observatory in Johannesburg, South Africa, discovered a star that had the same proper motion as Alpha Centauri.〔(Circular No. 30, 1915, October 12, of the Union Observatory (Proxima Centauri discovery paper).) )〕〔Go to (WayBackMachine ) INTERNET ARCHIVE. Enter In 1951, American astronomer Harlow Shapley announced that Proxima Centauri is a flare star. Examination of past photographic records showed that the star displayed a measurable increase in magnitude on about 8% of the images, making it the most active flare star then known. The proximity of the star allows for detailed observation of its flare activity. In 1980, the Einstein Observatory produced a detailed X-ray energy curve of a stellar flare on Proxima Centauri. Further observations of flare activity were made with the EXOSAT and ROSAT satellites, and the X-ray emissions of smaller, solar-like flares were observed by the Japanese ASCA satellite in 1995. Proxima Centauri has since been the subject of study by most X-ray observatories, including XMM-Newton and Chandra.〔 Because of Proxima Centauri's southern declination, it can only be viewed south of latitude 27° N.〔For a star south of the zenith, the angle to the zenith is equal to the Latitude minus the Declination. The star is hidden from sight when the zenith angle is 90° or more, i.e. below the horizon. Thus, for Proxima Centauri: :Highest latitude = 90° + −62.68° = 27.32°. See: 〕 Red dwarfs such as Proxima Centauri are far too faint to be seen with the naked eye. Even from Alpha Centauri A or B, Proxima would only be seen as a fifth magnitude star.〔(【引用サイトリンク】 title =Proxima Centauri UV Flux Distribution )〕 It has an apparent visual magnitude of 11, so a telescope with an aperture of at least 8 cm (3.1 in.) is needed to observe it, even under ideal viewing conditions—under clear, dark skies with Proxima Centauri well above the horizon. 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「Proxima Centauri」の詳細全文を読む スポンサード リンク
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