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The date of Easter varies in a manner too complicated to summarize in a simple formula, and in most years differs between the usage of Western and Eastern Christianity (and the usages of the countries where they are respectively more influential). Following the Council of Nicaea, the date for Easter was completely divorced from the Jewish calendar and its computations for Passover. Thereafter, in principle, Easter fell on the Sunday following the full moon that follows the Northern spring equinox (the so-called Paschal Full Moon). However, the vernal equinox and the full moon were not determined by astronomical observation. Instead, the Spring Equinox was fixed to fall on the 21st day of March, while the full moon (known as the ecclesiastical full moon) was fixed at 14 days after the beginning of the ecclesiastical lunar month (known as the ecclesiastical new moon). Easter thus falls on the Sunday after the ecclesiastical full moon. The ''computus'' is the procedure of determining the first Sunday after the first ecclesiastical full moon falling on or after 21 March and the difficulty arose from doing this over the span of centuries without accurate means of measuring the precise solar or lunar years. The model that was worked out assumes that 19 tropical years have the same duration as 235 synodic months (modern value: 234.997).〔Assuming a mean tropical year of 365.2421897 days as of 2000 and a long-term average synodal month of 29.530589 days. See tropical year and synodal month for details.〕 Since the 16th century, there have been differences in the calculation of Easter between the Western and Eastern Churches. The Roman Catholic Church since 1583 has been using 21 March under the Gregorian calendar to calculate the date of Easter, while the Eastern Orthodox continued and continue to use 20 March under the Julian Calendar. The Catholic and Protestant denominations thus use an ecclesiastical full moon that occurs four to five days earlier than the eastern one. == Earliest Easter == Western/Gregorian In 1818 the Paschal Full Moon fell on Saturday March 21 (the equinox). Therefore the following day, March 22, was Easter. It will not fall as early again until 2285 - a span of 467 years. A notably early, but not as such, Easter between 1818 and 2285 is 2008's Easter - March 23. It last occurred that early in 1913, and will occur again in 2160, a 95 and 152-year gap, respectively. Orthodox/ Julian The earliest dates for Orthodox Easter between 1875 and 2099 are, 22 March 1915 and 22 March 2010. Both dates are equivalent to April 4 in the Gregorian Calendar. 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「List of dates for Easter」の詳細全文を読む スポンサード リンク
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