Gregorian Calendar

Gregorian Calendar

The rules of calculations for Easter day were elaborated at the First Council of Nicaea in 325 A.D. The Christian Easter is celebrated on the first Sunday after the first Vernal equinox, but not earlier and not at the some day as Passover. Relating to the last situation the Emperor Constantine wrote from Nicaea to the bishops, who were absent from the Council, that "it seemed to the Council improper to perform the most Holy Holiday according to the custom of Israelites" because they "instead of the proper correction perform Easter two times at one and same year". It reflected the situation, that in Hebrew calendar may in fact be two Jewish Passovers between two Vernal equinoxes, and the length of the tropical year is determined as the period between two Vernal equinoxes.

In the determination of the Easter day it is assumed, that the Vernal equinox happens on March 21. It was exactly so in 325 A.D. But every 128 years the Julian calendar differs from the tropical year by 1 day, that's why March 21 is moving more and more from the date of the real astronomical equinox to the direction of Summer, and the Easter is moving alongside.

The Catholic Church several times discussed this problem at its Councils, and in 1582 A.D. the Pope, Gregory XIII carried out the calendar reform. The new style introduced by his decision has been called up till now the Gregorian calendar. However, it is worth mentioning that author of the reform was Italian mathematic and physician Aloysius Giglio. The Commission, established by the Pope�s order, chose his project.

The Pope Gregory XIII wrote in his special bulla on February 24, 1582 A.D. the following. "It was our concern not only to restore the equinox to the long time established place, which it moved away since the Nicean Council for approximately ten days, and to return it back by XIV Moon to the place, which it now moved away for four and five days, but to establish such method and rules, which will secure, that in the future equinox and the XIV Moon will never be moved from their places... That is why in order to return the Vernal equinox to its former place, which was established by the Nicean Council Fathers on the 12^th day before April calends (March 21), we order and command regarding the month of October of the current 1582 year, that ten days, from the third day before nones (October 6) to the eve of ides (October 14) including, be withdrawn".

So 10 days were omitted and October 15 immediately followed October 4, 1582 A.D. The successive course of week days not changed. Thus according to the intention of the reformers, the Vernal equinox returned to March 21. And so that it will never move in the future, the reform suggested, that every hundredth year, if its number is not divided by four without remainder, will be considered the non leap year, though by Julian calendar all there years should be called leap years. As a result, the difference between the medium length of the calendar year and the tropical year will be less and the divergence of one day between the Gregorian and Tropical year will be accumulated only during 2735 years and will be in the year of 4317 A.D.

Gregorian calendar was adopted initially only in the countries with strong Pope influence. Many others especially the Protestant countries opposed the reform. However gradually widely spread. The Russian Orthodox Church did not accept the new calendar at all. The matter was, that in Gregorian calendar Easter often coincides or happens before Jewish Passover, which is forbidden by Apostles' Rules.

On the occasion of the Easter date it is worth noting the following. As is known exactly every year the miracle of the beneficial Fire is coming down on the Holy God's Coffin in Jerusalem on Great Saturday. But the beneficial Fire appears only on the eve of the Resurrection Christ Sunday, determined by the Julian calendar and never goes down on the eve of the Easter, celebrated according to the Gregorian calendar.

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