<P> Easter is the third Sunday in the paschal lunar month, or, in other words, the Sunday after the paschal lunar month's 14th day . The 14th of the paschal lunar month is designated by convention as the Paschal full moon, although the 14th of the lunar month may differ from the date of the astronomical full moon by up to two days . Since the ecclesiastical new moon falls on a date from 8 March to 5 April inclusive, the paschal full moon (the 14th of that lunar month) must fall on a date from 21 March to 18 April inclusive . </P> <P> The Gregorian calculation of Easter was based on a method devised by the Calabrian doctor Aloysius Lilius (or Lilio) for adjusting the epacts of the moon, and has been adopted by almost all Western Christians and by Western countries which celebrate national holidays at Easter . For the British Empire and colonies, a determination of the date of Easter Sunday using Golden Numbers and Sunday letters was defined by the Calendar (New Style) Act 1750 with its Annexe . This was designed to match exactly the Gregorian calculation . </P> <P> The precise date of Easter has at times been a matter of contention . By the later 2nd century, it was widely accepted that the celebration of the holiday was a practice of the disciples and an undisputed tradition . The Quartodeciman controversy, the first of several Easter controversies, arose concerning the date on which the holiday should be celebrated . </P> <P> The term "Quartodeciman" refers to the practice of celebrating Easter on Nisan 14 of the Hebrew calendar, "the LORD's passover" (Leviticus 23: 5). According to the church historian Eusebius, the Quartodeciman Polycarp (bishop of Smyrna, by tradition a disciple of John the Apostle) debated the question with Anicetus (bishop of Rome). The Roman province of Asia was Quartodeciman, while the Roman and Alexandrian churches continued the fast until the Sunday following (the Sunday of Unleavened Bread), wishing to associate Easter with Sunday . Neither Polycarp nor Anicetus persuaded the other, but they did not consider the matter schismatic either, parting in peace and leaving the question unsettled . </P>

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