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An ecclesiastical full moon is formally the 14th day of the ecclesiastical lunar month (an ecclesiastical moon) in an ecclesiastical lunar calendar. The ecclesiastical lunar calendar spans the year with lunar months of 30 and 29 days which are intended to approximate the observed phases of the moon. Since a true synodic month has a length that can vary from about 29.27 to 29.83 days, the moment of astronomical opposition tends to be roughly 14.75 days after the previous conjunction of the sun and moon. The ecclesiastical full moons of the Gregorian lunar calendar tend to agree with the dates of astronomical opposition, referred to a day beginning at midnight at 0 degrees longitude, to within a day or so. However, the astronomical opposition happens at a single moment for the entire earth: The hour and day at which the opposition is measured as having taken place will vary with longitude. In the ecclesiastical calendar, the 14th day of the lunar month, reckoned in local time, is considered the day of the full moon at each longitude. Schematic lunar calendars can and do get out of step with the moon. A useful way of checking their performance is to compare the variation of the astronomical new moon with a standard time of 6 A.M. on the last day of a 30 - day month and 6 P.M. (end of day) on the last day of a 29 - day month. In the medieval period the age of the ecclesiastical moon was announced daily in the office of Prime at the reading of the martyrology.〔At medieval Exeter Cathedral, it was the next day's date and age of the moon that were announced. ''Et omnibus in locis suis sedentibus sit ibi quidam puer...paratus ad legendum leccionem de Martilogio, absque Iube domine, sed pronunciondo primo loco numerum Nonarum, Iduum, Kalendarum, et etatem lune qualis erit in crastino...'' (And when all are sitting in their places let a boy be there ready to read the Martyrology beginning with Iube domine, but first saying the number of Nones, Ides, Kalends, and what the age of the moon will be on the morrow...) J.N. Dalton, ed., ''Ordinale Exon.'' vol. 1, Henry Bradshaw Society, London, 1909, p. 37.〕 In the Book of Common Prayer of the Protestant Episcopal Church of the United States of America, the dates of the paschal full moons for the 19 years of the Gregorian Easter cycle are indicated by the placement of the Golden Number to the left of the date in March or April on which the paschal full moon falls in that year of the cycle.〔''The Book of Common Prayer according to the use of The Episcopal Church'', Seabury Press, New York, pp. 21-22.〕 The same practice is followed in some editions of the Book of Common Prayer of the Church of England. ==Paschal full moon== Notionally, the ''paschal full moon'' refers to the ecclesiastical full moon of the northern spring used in the determination of the date of Easter. The name "paschal" is derived from "Pascha", a transliteration of the Greek word, which is itself a transliteration of the Hebrew ''pesach'', both words meaning Passover. The date of Easter is determined as the first Sunday after the "paschal full moon" falling on or after the Spring Equinox (March 21). This "full moon" does not currently correspond directly to any astronomical event, but is instead the 14th day of a lunar month, determined from tables. It may differ from the date of the actual full moon by up to two days.〔Montes, Marcos J. ("Calculation of the Ecclesiastical Calendar" ) Retrieved on 2008-01-12〕 The use of tables instead of actual observations of the full moon is useful and necessary since the full moon may occur on different dates depending where one is in the world. The calculations to determine the date of the paschal full moon are somewhat complex, but can be described briefly as follows: * Nineteen civil calendar years are divided into 235 lunar months of 30 and 29 days each (the so-called "ecclesiastical moon".) * The period of 19 years (the metonic cycle) is used because it produces a set of civil calendar dates for the ecclesiastical moons that repeats every nineteen years while still providing a reasonable approximation to the astronomical facts. * The first day of each of these lunar months is the ecclesiastical new moon. Exactly one ecclesiastical new moon in each year falls on a date between March 8 and April 5, both inclusive. This begins the paschal lunar month for that year, and thirteen days later (that is, between March 21 and April 18, both inclusive) is the paschal full moon. * Easter is the Sunday following the paschal full moon. In other words, Easter falls from one to seven days after the paschal full moon, so that if the paschal full moon is on Sunday, Easter is the following Sunday. Thus the earliest possible date of Easter is March 22, while the latest possible date is April 25. 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「Ecclesiastical full moon」の詳細全文を読む スポンサード リンク
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