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Spica
Spica (; α Vir, α Virginis, Alpha Virginis) is the brightest star in the constellation Virgo, and the 15th brightest star in the night sky. Located 250 ± 10 light years from Earth, it is actually a spectroscopic binary and rotating ellipsoidal variable—a system whose two main stars are so close together they are egg-shaped rather than spherical, and can only be separated by their spectrum. The primary is a blue giant and a variable star of the Beta Cephei type.
==Observation history==
Spica is believed to be the star that gave Hipparchus the data that led him to discover the precession of the equinoxes.〔 A temple to Menat (an early Hathor) at Thebes was oriented with reference to Spica when it was built in 3200 BC, and, over time, precession slowly but noticeably changed Spica's location relative to the temple.〔 Nicolaus Copernicus made many observations of Spica with his home-made triquetrum for his researches on precession.〔〔
As one of the nearest massive binary star systems to the Sun, Spica has been the subject of many observational studies.〔
Analysis of its parallax shows that it is 250 ± 10 light years from Earth.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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