The Paschal Full Moon roughly corresponds to the first full moon of the northern Spring. The name 'Paschal' is from "Pascha" which is 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. This full moon does not currently correspond directly to any astronomical event, but is a historical artifact determined from tables, and it may differ from the date of the actual full moon by up to two days.^[1] 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.

Historically, the Paschal Full Moon was the first full moon which occurs on or after the day of the vernal equinox. Later, the Paschal Full Moon referred to the day which was thirteen days after the Ecclesiastical new moon. The calculations to determine the date of the Paschal Full Moon are somewhat complex. For a detailed discussion, see Computus.

If the Paschal Full Moon falls on a Sunday, Easter is the following Sunday.

Easter Tables

In the course of the third century Easter tables, tables with which dates of Easter Sunday can be found, came in use. In the beginning of the third century computists of some churches, among which were the church of Rome and the one of Alexandria, had gone to calculate their own periodic sequences of dates of Paschal full moon, to be able to determine their own dates of Easter Sunday^[2].

To be able to develop those early Easter tables, owing to the then incalculability of the Hebrew calendar, one had been forced to substitute the dates of the fourteenth day of Nisan, preparation day of the Jewish Passover, for dates of the Paschal full moon adapted to either the Julian calendar used in Rome or the Egyptian calendar used in Alexandria. Obviously periodic sequences of dates of the Paschal full moon and incalculable sequences of dates of the fourteenth day of Nisan, initially as few different as possible, could in no case entirely tally with each other. But ultimately, in connection with the determination of the spring equinox on 21 March, the ?adjustment of Nisan? to the Egyptian calendar around the year 300 as well as the one to the Julian calendar around the year 400 went hand in hand with a relatively considerable shift in time of roughly two days. During four centuries the sequences of dates of the Paschal full moon plied by the different churches could show great differences, which was the main cause of the fact that the Easter tables propagated then by the different churches often differed strongly and did not lead to the same dates being eligible for the celebration of Easter Sunday.

References

See also

• Computus
• Easter - Date of Easter
• Ecclesiastical new moon
• Golden numbers
• Reform of the date of Easter
• Dionysius Exiguus' Easter table

External links

• Algorithim to calculate the date of the Paschal Full Moon

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