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The term Great Year has a variety of related meanings. It is defined by NASA as "The period of one complete cycle of the equinoxes around the ecliptic, about 25,800 years () also known as () Platonic Year." One complete cycle of the equinoxes here means one complete cycle of axial precession; this precession was known to Plato, who defined the "perfect year" as the return of the celestial bodies (planets) and the diurnal rotation of the fixed stars (circle of the Same) to their original positions. Cicero followed Plato in defining the Great Year as a combination of solar, lunar and planetary cycles (61 XX) Nicholas Campion writes of "periods of History, analogous to the solar year, known as 'Great Years' " 〔Nicholas Campion, "The Great Year: Astrology, Millenarianism and History in the Western Tradition" (Arkana/Penguin Books, 1994), p. 6.〕 Plato's description of the perfect year is found in his dialogue ''Timaeus'' In ''De Natura Deorum'', Cicero wrote By extension, the term "Great Year" can also be used for any concept of eternal return in the world's mythologies or philosophies. Otto Neugebauer wrote Macrobius in his commentary on Cicero's Somnium Scipiones states that 'the philosophers' reckon the Great Year as 15,000 years. (p. 97) Censorinus wrote that Aristarchus of Samos reckoned a Great Year of 2484 years: it has been argued that this is a miscopying of 2434, which represents 45 Exeligmos cycles.〔 (p. 96) 〔http://www.dioi.org/vols/wb1.pdf〕 (p. 6) The Platonic Year in origin would seem to have no connection with this concept (as the precession of the equinox was unknown to Europe in Plato's time).〔William Harris Stahl, "Macrobius: Commentary on the Dream of Scipio" (Columbia University Press, 1952), p. 21〕 and two centuries after Plato, Hipparchus is credited with discovering the period of equinox precession, and the term "Great Year" eventually came to be applied to the period of that precession caused by the slow gyration of the Earth's axis. It is argued that the confusion originates with the astronomer Ptolemy, who "adopted the larger, erroneous, figure, with the result that henceforth the two versions of the Great Year — the Platonic Great Year, defined by the planets, and the precessional, defined by the stars — were to be increasingly confused."〔Nicholas Campion, "The Great Year: Astrology, Millenarianism and History in the Western Tradition" (Arkana/Penguin Books, 1994), p. 246–247.〕 Ptolemy has been accused of committing scientific fraud by making up observations that would give the figure of 36,000 years even though the data available to him were good enough to get very near the true figure of 26,000.〔R.R.Newton, "The Authenticity of Ptolemy's star data" (())〕 Josephus refers to a 'Great Year' () of 600 years.〔http://www.sacred-texts.com/jud/josephus/ant-1.htm〕 (ch.4) It has been suggested that he obtained this value from Berossos who reckoned time in intervals of 60, 600 and 3600 years.〔Josephus, ''Jewish Antiquities'', Loeb, p.1, note a,〕 Isaac Newton determined the cause of precession and established the rate of precession at 1 degree per 72 years, very close to the true value, thus demonstrating the magnitude of the error in the value of 1 degree per century. (letter 17) Walter Cruttenden wrote of the Great Year ==See also== *Astrological age *Axial precession (astronomy) *Precession *Precession: Astronomy *Yuga 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「Great Year」の詳細全文を読む スポンサード リンク
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