Hi Feo,
There is a really good coptic website which explains why, but because unfortunately I'm a newbie, the forum doesnt allow me to post it, so I'm going to cut and paste from the website as it has a detailed explanation:
"the Christians since the start found it important to celebrate the Crucifixion and Resurrection of our Lord. And, since the dates of these two events were linked to the Jewish Passover, the faithful preferred to keep the tradition of tying glorious feast of the Resurrection to the Passover, yet celebrating it afterwards, so that we may not partake in their feasts. The teachings of the apostles stated that whoever celebrates the Resurrection on a day other than the Sunday (that follows the Jewish Passover) is partaking with the Jews in their feasts, and has separated himself from the Christians.
The determination of the date of the Resurrection feast remained a matter of research and change, until Pope Demetrius, the 12th Patriarch of Alexandria, concerned himself with it, consulted the Scientists of his time, such as Ptolemeus Farmawy, and came up with the APAKTY (Remainder) calculation, on the basis of which the dates of the Great Fast, the Resurrection, Pentecost and the length of the apostles' fast are determined. Pope Demetrius sent his formula to the patriarchs of the other churches, who accepted it and celebrated according to it.
When the first Ecumenical Council convened at Nicea, in 325 AD, it endorsed and confirmed the Apakty calculation. The resolution of the council was that the Patriarch of Alexandria was to determine the date of the Resurrection feast according to this formula and to send to the whole world the dates of the start of Great Fast and of the feast of the Resurrection, together with a paschal letter to be read in the whole world on the Christian Pascha (Resurrection.)
Briefly, the Apakty formula is a means of calculating the full moon following the vernal equinox, and the date of the slaying of the Passover lamb. We celebrate the Resurrection on the Sunday following these dates.
And since the cycle of the Julian (Roman) or Coptic year (i.e. the period after which the day of the year falls on the same day of the week of the previous cycle) is 28 years (every 28 years are identical as far as the starts and ends of their months and weeks), and since the cycle of the Jewish year, the basis of calculation of the Jewish Passover, is 19 years (every 19 Jewish years are similar in the starts and ends of their months), so the date of the resurrection feast is the same every 19x28 years, i.e. every 532 years. Some have written tables, called vines, of 532 years, to determine the dates of Great Fast and feasts in every year of the cycle according to the Coptic calendar.
The whole Christian world celebrated according to these vines and formula until the sixteenth century, when Pope Gregory of Rome changed the Roman calendar. He established a different calculation for the feast of the Resurrection, a clear infraction against the canon of Nicene council, which had confirmed the Apakty calculation and had given the Patriarch of Alexandria the right to set the feast's date.
Pope Gregory decided to set the date to be the Sunday following the full moon following the vernal equinox, not considering the Passover Lamb, nor the canon of the council of Nicea, nor the spirituality of the teachings of the holy apostles, which urge us not to celebrate at the same time as the Jews. The Western world now celebrates according to these innovations. The year (2002) for instance, the Jews had set their Passover, according to the renovated vernal equinox of Pope Gregory, to be 27 March. And the Western churches are celebrating Easter on 31 March, while according to our canonical calculation, established by the holy fathers, the slaying of the Passover lamb should be on 23 Barmuda (1 May), thus making our Resurrection feast on Sunday 27 Barmuda (5 May).
May the blessing of the Resurrection of our Lord and Savior Jesus Christ be upon us all. Amen."
Please let me know if you have any further quiries and I'm more than happy to explain it to you, if the above explanation was too confusing. But basically, the main point is, we celebrate easter after the Jewish Passover. The Jewish Passover this year ends on 28th of April and the Easter is on 1st of May.
love and blessings
erini
