Question from Louise on 4/4/2008:
A friend who is a member of the Russian Orthodox church told me last week that she was observing Lent and is looking forward to Easter. I realize they are on a different calendar than other Christians but don't understand why and when this happened.
Answer by Matthew Bunson on 4/7/2008:
The differences in celebration stem from the fact that the Catholic Church and Orthodox use different calendars for the calculation of Easter and the rest of the liturgical year.
The Church uses the Gregorian Calendar that was first introduced in 1582 under Pope Gregory XIII in order to fix the massive problems that had accumulated over the centuries in the Julian Calendar (the ancient calendar first devised by Julius Caesar to fix the problems of time in his own era).
As the Julian Calendar was far from perfect, errors did indeed begin to creep into the keeping of time. Owing to the inherent imprecision of the calendar the calculated year was too long by 11 minutes 14 seconds. The problem only grew worse with each passing year as the equinox slipped backwards one full day on the calendar every 130 years. For example, at the time of its introduction, the Julian Calendar placed the equinox March 25th and by the time of the Council of Nicea in 325, the equinox had fallen back to March 21st. By 1500, the equinox had shifted by ten days. Needless to say, this had great consequences on calculating the date for Easter.
Having decreed months before that a reform of the calendar was essential for the good of Western civilization, Pope Gregory XIII (pope from 1572 to 1585) made the implementation of a new calendar effective on the night of October 4. The next day, part of the massive fix of the Julian Calendar, was not counted as October 5 but October 15, 1582. Of course, in a post-Reformation Europe, the new computations were greeted with suspicion in the lands that were no longer Catholic. Protestant Germany adopted the calendar slowly: Prussia accepted it in 1610, while the rest of the Protestant states decreed it only in 1700.
Russia and the Eastern Orthodox Churches rejected the new calendar and continued to use the Julian Calendar in their calculations for Easter. The Gregorian Calendar was accepted as the civic calendar in Russia only after the Russian Revolution in 1917. The Eastern Orthodox continue to use a revised Julian Calendar, with the exception, I believe, of the Finnish Orthodox Church, which adopted the Gregorian Calendar.