Frequently Asked Questions
Why are there differences in the dating of Easter?
The Council of Nicaea in the fourth century decreed that Easter should be celebrated on the first Sunday after the first full moon after the spring equinox.
Differences in dating occur because churches follow different calculations of the equinox and the full moon. Astronomical determinations of the equinox and full moon also depend on the position on Earth used as a point of reference ( e.g. Jerusalem ).
The churches of the East and West typically celebrate Easter on the same date once every three or four years. In the other years they are typically one, four or five weeks apart.
taken from the Orthodox Christian Information Center
for more detail: U.S. Naval Observatory, Astronomical Applications Dept
Why are there differences in the dating of Christmas?
Christmas is celebrated on December 25, But ...
Some Orthodox celebrate Christmas on December 25 of the "old" calendar ("Julian Calendar"), and some celebrate on December 25 of the modern revised calendar ("Gregorian Calendar"). December 25 in the Julian Calendar is January 7 of the "new" Gregorian Calendar.
The Gregorian Calendar (sometimes called the Revised Julian Calendar) was adopted as the secular calendar in 1585 in parts of Western Europe, in 1753 in England and North America, and 1923 in Russia.
The two days when Christmas is celebrated will actually drift apart an extra three days every 400 years. December 25 in the Julian Calendar will be January 8 in the secular (Gregorian Calendar) starting in the year 2100.