復活節的計算方法復活節會在每年春分月圓之後第一個星期日舉行，因為春分之後便開始日... of EasterIn Western Christianity, Easter Day always falls on a Sunday between March 22 and April 25 inclusive. The following day, Easter Monday, is recognized as a legal holiday in most countries with a generally Christian tradition, but not as a rule in the United States, except formerly in a few states, all of which had dropped it by the 1980s. Easter and the holidays that are related to it are moveable feasts, in that they do not fall on a fixed date in the Gregorian or Julian calendars (which follow the motion of the sun and the seasons). Instead, they are based on a lunar calendar similar—but not identical—to the Hebrew Calendar. The precise date of Easter has often been a matter for contention. At the First Council of Nicaea in 325 it was decided that Easter would be celebrated on the same Sunday throughout the Church, but it is probable that no method was specified by the Council (unfortunately no verbatim account of the Council's decisions has survived). Instead, the matter seems to have been referred to the church of Alexandria, which city had the best name for scholarship at the time. The practice of this city was to celebrate Easter on the first Sunday after the earliest fourteenth day of a lunar month that occurred on or after March 21. During the Middle Ages this practice was more succinctly phrased as Easter is observed on the Sunday after the first full moon on or after the day of the vernal equinox. The Church of Rome used its own methods to determine Easter until the 6th century, when it may have adopted the Alexandrian method as converted into the Julian calendar by Dionysius Exiguus (certain proof of this does not exist until the ninth century). Most churches in the British Isles used a late third century Roman method to determine Easter until they adopted the Alexandrian method at the Synod of Whitby in 664. Churches in western continental Europe used a late Roman method until the late 8th century during the reign of Charlemagne, when they finally adopted the Alexandrian method. Since western churches now use the Gregorian calendar to calculate the date and Eastern Orthodox churches use the original Julian calendar, their dates are not usually aligned in the present day. At a summit in Aleppo, Syria, in 1997, the World Council of Churches proposed a reform in the calculation of Easter which would have replaced an equation-based method of calculating Easter with direct astronomical observation; this would have side-stepped the calendar issue and eliminated the difference in date between the Eastern and Western churches. The reform was proposed for implementation starting in 2001, but it was not ultimately adopted by any member body. See Reform of the date of Easter. A few clergymen of various denominations have advanced the notion of disregarding the moon altogether in determining the date of Easter; proposals include always observing the feast on the second Sunday in April, or always having seven Sundays between the Epiphany and Ash Wednesday, producing the same result except that in leap years Easter could fall on April 7. These suggestions have yet to attract significant support, and their adoption in the foreseeable future is deemed unlikely. ComputationsThe calculations for the date of Easter can be somewhat complicated. See computus for a discussion covering both the traditional tabular methods and more exclusively mathematical algorithms such as the one developed by mathematician Carl Friedrich Gauss. In the Western Church, Easter has not fallen on the earliest of the 35 possible dates, March 22, since 1818, and will not do so again until 2285; it fell on the latest possible date, April 25 most recently in 1943, and will next fall on that date in 2038. Historically, other forms of determining the holiday's date were also used. For example, Quartodecimanism was the practice of setting the holiday on the 14th day of the Jewish month of Nisan, which is the day of preparation for Passover.