EWTN Catholic Q&A
Origins of Christmas and Easter holidays
Question from Anne G on 10-20-2007:

How where the dates for Easter and Christmas decided? When was this done and why those times? Who made these decisions?

Answer by Matthew Bunson on 10-21-2007:

In the early Church, the feast of Our Lord's Birth was celebrated at the same time as Epiphany. The actual date of Our Lord’s birthday is unknown, despite the best efforts of scholars and theologians. It can be guessed, for example, that the census imposed by the Roman Empire was likely held during a time of year when travel would be easy, perhaps spring. This is pure speculation, of course. The earliest effort to calculate the exact date, however, is traced back to the 3rd century and Clement of Alexandria who placed the day at May 20. The commemoration in the early Church – for at least the first three centuries – was the Feast of the Manifestation (Epiphany, on January 6). According to the Philocalian Calendar – representing practice in Rome in 366 – December 25 was listed as natus Christus in Betleem Judaea. It is suggested by Catholic scholars that the date was chosen to oppose the pagan festival of Natalis Solis Invicti, the celebration of the Sol Invictus in the Roman pantheon. Once accepted in Rome, the celebration of Christmas on Dec. 25 spread throughout the Church. The Council of Tours (567) decreed the 12 days from Christmas to Epiphany to be sacred and especially joyous, thus setting the stage for the celebration of the Lord’s birth not only in a liturgical setting but in the hearts of all Christians.

As for Easter, there is a very complicated set of calculations used for the determination of the date each year. As I understand such things, Easter is celebrated on the first Sunday after the full moon following the vernal equinox (between Mar. 22 and Apr. 25). The Astronomical Society of Southern Australia has a detailed website on this topic: http://www.assa.org.au/edm.html#Method. You might also read the excellent article in the Catholic Encyclopedia: http://www.newadvent.org/cathen/05224d.htm.

There were several controversies in the first centuries of the Church as to what system should be used for finding the correct date for Easter. For example, there were those who proposed that that the observance should be strictly on 14 Nisan or whether, more logically, it should be on the following Sunday to match the events clearly recounted in the Gospels. The adherents of the former system became known as the Quartodecimans, and other different groups favored different dates for the celebrations, based chiefly on two methods of calculating the date that were favored in either Rome or Alexandria based on so-called paschal cycles. From the 5th century, Roman officials began seeing the advantages to the Alexandrian calculations (as the Alexandrians had more accurate astronomical resources). In 525, Dionysius Exiguus accepted officially the Alexandrian computation, and it was subsequently, albeit only gradually, applied to the whole of the Western Church. One longstanding exception was the Church in the British Isles, the Celtic Church. Finally, in 664 the Synod of Whitby decreed that the Roman custom should be applied in England; this was enforced with great enthusiasm by Archbishop Theodore of Canterbury.