Ancient Christian Witness

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Why does the date for Easter change every year?
Have you ever wondered why Easter Sunday can fall anywhere between March 22 and
April 25? And why do Eastern Orthodox churches celebrate Easter on a different
day than Western churches? These are all good questions with answers that
require a bit of explanation.

In Western Christianity, Easter is always
celebrated on the Sunday immediately following the Paschal Full Moon date of the
year. I had previously, and somewhat erroneously stated, "Easter is always
celebrated on the Sunday immediately following the first full moon after the
vernal (spring) equinox." This statement was true in 325 AD, when it was
established by the Council of Nicea. However, the course of history has modified
the meaning of this instruction, and therefore, a clearer, more accurate
explanation is necessary today.

There are, in fact, as many
misunderstanding about the calculation of Easter dates, as there are reasons for
confusion about Easter dates. What follows is an attempt to clear up at least
some of the confusion.

In actuality, the date of the Paschal Full Moon
is determined from historical tables, and has no correspondence to lunar events.
In the year 325 AD astronomers approximated the dates of all the full moons in
the year for the Western Christian churches. These were called the
Ecclesiastical Full Moon dates, and they have been used ever since 326 AD to
determine the date of Easter. So, the Paschal Full Moon is always the first
Ecclesiastical Full Moon date after March 20 (which happened to be the vernal
equinox date in 325 AD).

The Paschal Full Moon can vary as much as two
days from the date of the actual full moon, with dates ranging from March 21 to
April 18. As a result, Easter dates can range from March 22 through April 25 in
Western Christianity.

Western churches use the Gregorian Calendar to
calculate the date of Easter and Eastern Orthodox churches use the Julian
Calendar. This is partly why the dates are rarely the same.

Easter and
its related holidays do not fall on a fixed date in either the Gregorian or
Julian calendars, making them moveable holidays. The dates, instead, are based
on a lunar calendar very similar to the Hebrew Calendar.

The Eastern
Orthodox Church not only maintains the date of Easter based on the Julian
Calendar which was in use during the First Ecumenical Council of Nicea in 325
AD, but also according to the actual, astronomical full moon and the actual
vernal equinox as observed along the meridian of Jerusalem. This complicates the
matter, due to the inaccuracy of the Julian calendar, and the 13 days that have
accrued since 325 AD. This means, in order to stay in line with the originally
established (325 AD) vernal equinox, Orthodox Easter cannot be celebrated before
April 3 (present day Gregorian calendar), which was March 21 in 325 AD.

Additionally, in keeping with the rule established by the First
Ecumenical Council of Nicea, the Eastern Orthodox Church adhered to the
tradition that Easter must always fall after the Jewish Passover, since the
death, burial and Resurrection of Christ happened after the celebration of
Passover. Eventually the Orthodox Church came up with an alternative to
calculating Easter based on Passover, and developed a 19-year cycle, as opposed
to the Western Church 84-year cycle.

Since the days of early church
history, determining the precise date of Easter has been a matter for continued
argument. For one, the followers of Christ neglected to record the exact date of
Jesus' resurrection. From then on the matter grew increasingly complex. For more
about Easter dates, check out the following sources: