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Regulus (α Leo, α Leonis, Alpha Leonis) is the brightest star in the constellation Leo and one of the brightest stars in the night sky, lying approximately 79 light years from Earth.〔 Regulus is a multiple star system composed of four stars that are organized into two pairs. The spectroscopic binary Regulus A consists of a blue-white main-sequence star and its companion, which has not yet been directly observed, but is probably a white dwarf. Located farther away is the pair Regulus B and Regulus C and D, which are dim main-sequence stars. == Observations == Regulus is 0.46 degree from the ecliptic, the closest of the bright stars, and is regularly occulted by the Moon. Occultations by the planets Mercury and Venus are possible but rare, as are occultations by asteroids. The last occultation of Regulus by a planet was on July 7, 1959, by Venus.〔 The next will occur on October 1, 2044, also by Venus. Other planets will not occult Regulus over the next few millennia because of their node positions. An occultation of Regulus by the asteroid 166 Rhodope was observed by 12 researchers from Portugal, Spain, Italy, and Greece on October 19, 2005. Differential bending of light was measured to be consistent with general relativity. Regulus was occulted by the asteroid 163 Erigone in the early morning of March 20, 2014. The center of the shadow path passed through New York and eastern Ontario, but no one is known to have seen it, due to cloud cover. The International Occultation Timing Association recorded no observations at all.〔(Regulus 2014 ) International Occultation Timing Association〕 Although best seen in the evening in northern hemisphere in late winter and spring, Regulus appears at some time of night throughout the year except for about a month on either side of August 22, when the Sun is too near. Regulus passes through SOHO's LASCO C3 every August.〔 For most Earth observers, the heliacal rising of Regulus occurs in the first week of September. Every 8 years, Venus passes Regulus around the time of the star's heliacal rising, as on 5 September 2014. The primary of Regulus A has about 3.5 times the Sun’s mass and is apparently a young star only a few hundred million years. It is spinning extremely rapidly, with a rotation period of only 15.9 hours, which causes it to have a highly oblate shape. This results in so-called gravity darkening: the photosphere at Regulus' poles is considerably hotter, and five times brighter per unit surface area, than its equatorial region. If it were rotating only 15% faster, the star's gravity would be insufficient to hold it together, and it would spin itself apart.〔 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「Regulus」の詳細全文を読む スポンサード リンク
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