The
paschal full moon is the particular 'ecclesiastical full moon' that is used in the calculation of the
date of Easter. The name
paschal is derived from
Pascha, a transliteration of the
Aramaic word meaning
Passover. This 'paschal full moon' is the one that falls on or after March 21. (March 21 is the
ecclesiastical equinox, the date fixed by the
Gregorian reform of the calendar as a fixed reference date for the
Spring Equinox in the Northern hemisphere; the actual Equinox can fall on March 19, 20 or 21). The date of Easter is determined as the first Sunday after that specific full moon. This "full moon" does not necessarily 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 or even three days. The calculations to determine the date of the paschal full moon can be described as follows: • Nineteen civil calendar years are divided into 235 lunar months of 30 and 29 days each. • This 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.
Earliest Easter In 1818, as the paschal full moon fell on Saturday March 21 (the ecclesiastical fixed date for the Equinox), Easter was the following day—Sunday March 22—the earliest date possible. It will not fall on this date again until 2285, a span of 467 years.
Latest Easter In 1943 an ecclesiastical full moon fell on Saturday March 20. As this was before March 21, the next ecclesiastical full moon, which fell on Sunday April 18, determined the date of Easter—the following Sunday, April 25. It will not fall on this date again until 2038, a span of 95 years. For a detailed discussion of the paschal computations, see
Date of Easter (the Computus).
Easter tables By the middle of the third century AD, computists of some churches, among which were the
Church of Rome and the
one of Alexandria, had begun to calculate their own periodic sequences of dates of paschal full moon, to be able to determine their own dates of
Easter Sunday. The motivation for these experiments was a dissatisfaction with the Jewish calendars on which Christians had hitherto used as their basis to fix the date of Easter. These Jewish calendars, according to their Christian critics, sometimes placed Nisan 14, the paschal full moon and the day of preparation for the Jewish Passover, before the spring equinox (see
Easter). The Christians, who began the experiments with independent computations, held that the paschal full moon should never precede the equinox. The computational principles developed at Alexandria eventually became normative, but their reception was a centuries-long process during which Alexandrian Easter tables competed with other tables incorporating different arithmetical parameters. So for a period of several centuries the sequences of dates of the paschal full moon applied by different churches could show great differences (see
Easter controversy). In the
Book of Common Prayer of the
Episcopal Church 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., ==See also==