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==The date of Easter==
According to Christian tradition, Jesus died at the ninth hour (that is, the canonical hour of nona or 'noon' in Middle English - 3:00 pm) of the first full day of Pesach, when that day fell on a Friday; and arose from the dead at or by the first (canonical) hour of that Sunday. The day of Pesach ([[Pascha]] or Passover, Nisan 14), is always at the first or second full moon following the vernal equinox. At the [[First Ecumenical Council]], held in 325 at Nicaea, it was decided to celebrate Easter on the Sunday following the so-called Paschal full moon. The Paschal full moon is an arithmetical approximation to the first full moon after the vernal equinox. It may be expressed as follows in terms of the so-called Golden number (G) and Century term (C): *Paschal full moon (PFM) = ([[April 19|19 April]], or 50 March) - (C+11G) mod 30 Except in two cases where the PFM is one day earlier than this, namely: *When (C+11G) is 0 modulo 30, PFM = [[April 18|18 April]] (not 19 April). *When (C+11G) is 1 modulo 30, and G=12, PFM = [[April 17|17 April]] (not 18). The Golden number (G) is the same for both Julian and Gregorian computations, but the Century term is constant (C = +3) in Julian computations: [[Image:CopticEasterComputations.jpg]] C is -4 from 1583 to 1699, -5 from 1700 to 1899, -6 from 1900 to 2199, -7 from 2200 to 2299 etc... As the Sunday following the PFM, Easter is one week after the PFM when the PFM happens to fall on a Sunday. One must work with the Julian calendar (C = +3) to find when Easter is celebrated by Orthodox churches.
At the Council of Nicaea, it became one duty of the Coptic [[Pope]] of Alexandria to determine the exact dates of Easter and to announce it to the rest of the Christian churches (see [http://www.copticcentre.com/copticsaints.html#Pope%20Demetrius%20The%20Vinedresser Pope Demetrius the Vinedresser, 3rd cent.]). This duty fell on this officate because of the erudition at Alexandria he could draw on. The precise rules to determine this are very involved, but Easter is usually the first Sunday after a full moon occurring no sooner than March 21, which was the actual date of the vernal equinox at the time of the First Council of Nicaea. Shortly before Julius Caesar reformed the calendar, the vernal equinox was occurring on the "nominal" date of March 25. This was abandoned at Nicaea, but the reason for the observed discrepancy was all but ignored (the actual tropical year is not quite equal to the Julian year of 365¼ days, so the date of the equinox keeps creeping back in the Julian calendar).
== Sources and external links ==
* [http://www.copticheritage.org/PagEd+index-page_id-828.phtml Coptic Calendar article in pdf]. ''The greatest article that sketches the history and development of the Coptic Calendar, and provides the ancient Alexandrian method of the Easter Computus.''
* [http://www.copticchurch.net/easter.html An introduction to the Coptic calendar] - ''Includes an online Coptic Holidays and Easter calculator''
* [http://www.copticchurch.org/Texts/Spirituals/Coptcaln.pdf '''''The Coptic Calendar and Church of Alexandria''''' - by the Very Rev. Fathers Tadros Y. Malaty and Matta El-Meskeen (PDF)]
