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}} Rigel, also known by its Bayer designation Beta Orionis (β Ori, β Orionis), is the brightest star in the constellation Orion and the seventh brightest star in the night sky, with visual magnitude 0.13. The star as seen from Earth is actually a triple star system, with the primary star (Rigel A) a blue-white supergiant of absolute magnitude −7.84 and around 120,000 times as luminous as the Sun. It has exhausted its core hydrogen and swollen out to 79 times the Sun's radius. An Alpha Cygni variable, it pulsates periodically. Visible in small telescopes and 500 times fainter than Rigel A, Rigel B is itself a spectroscopic binary system, consisting of two main sequence blue-white stars of spectral type B9V that are themselves estimated to be 2.5 and 1.9 times as massive as the Sun. == Visibility == The apparent magnitude of Rigel is listed in the astronomical database SIMBAD at 0.13, making it on average the seventh brightest star in the celestial sphere excluding the Sun—just fainter than Capella. It is an irregular pulsating variable with a visual range of magnitude 0.05–0.18. Although Rigel has the Bayer designation "beta", it is almost always brighter than Alpha Orionis (Betelgeuse). Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.〔 Rigel is the third most inherently luminous first magnitude star after Deneb and Betelgeuse. Rigel has a color index (B–V) of −0.03, meaning it appears white or lightly blue-white. Culminating at midnight on 12 December, and at 9 pm on 24 January, Rigel is most visible in winter evenings in the northern hemisphere and summer in the southern. In the southern hemisphere, Rigel is the first bright star of Orion visible as the constellation rises. In stellar navigation, Rigel is one of the most important navigation stars, since it is bright, easily located and equatorial, which means it is visible all around the world's oceans (the exception, areas within 8° of the North Pole). 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「Rigel」の詳細全文を読む スポンサード リンク
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