What connection is there between the Alexandrian Computus (Epact) and the Christian Pascha?

The difficulty in determining the date of Christian Pascha (Holy Week and Resurrection) for each year is due to the ancient condition it must fall after the Jewish Passover. Since the Jewish Passover is linked to the harvest for the Jews (Ex. 23:16), it always falls in the months of April or May; bearing in mind that the Jewish calendar is lunar. However, this calculation does not correspond to the seasons of Egypt because the time of harvest in Egypt differs from that in Palestine. Therefore, Pope Demetrius of Alexandria (second century) saw the need to devise a calculation that combines the solar cycle with the lunar cycle; according to which the Christian Pascha falls in the months of April or May, but not before the first week of April and not later than the first week of May.

This calculation consists of a cycle of nineteen solar-lunar years. Since the lunar year is eleven days shorter than the solar year, the number of days missing in nineteen lunar years from the corresponding number of solar years is two hundred and nine days. He distributed these days over nineteen years by adding a full month every two or three years. The Council of Nicaea approved this computation, and the Church observed it all over the world until the year 1582 A. D.

The Protestants broke away from the Roman Church in the sixteenth century. This was the same century in which the Roman Pope Gregory XIII requested that the Jewish Passover not be taken into account in the computation of the Christian Pascha, but that it is sufficient

636 See Iris Habib El-Masry, The Story of the Copts: Book 1 , (Southern California, U.S.A: St. Anthony Coptic Orthodox Monastery, undated) 4.A.24: p. 39.

only to take into account the time of the spring equinox. Protestants continued to use the Alexandrian computus until 1775 A. D., that is for about two centuries.