How is the date for Easter calculated each year?

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2014-04-20 07:12:56

Easter Sunday typically falls on a different date each year.

Easter is always the first Sunday after or on the first full moon,

after the Spring (vernal) Equinox in the Northern

hemisphere and the Autumnal Equinox in the

Southern hemisphere.

The date is determined by a combination of events centered

around the lunar cycle, the solar cycle, the division of each year

into 365 days and a 1,700 year old Church ruling.

The explanation starts with the fact that early Christians

elected to link the date of Easter to the Hebrew calendar. The New

Testament states that the Resurrection took place on the first day

of the week following Passover. Sunday is the first day of a Jewish

week; the Passover falls on the day of the first full moon after

the Spring Equinox, which can fall on either March 20 or 21.

Chaotic, or what? The result was that different churches ended

up celebrating Easter on various days. And to try to clear up the

confusion, the Roman Emperor Constantine I organized a major summit


The first Ecumenical Council was held at Nicea in present-day

Turkey in the year 325. It decreed that Easter would be celebrated

on the Sunday following the first full moon that occurred after the

Spring Equinox. This retained a lunar connection as a sort of

"memory" of the Jewish calendar system, and ensured that the feast

would be on a Sunday. Because lunar phases occur independently of

the solar year, this means that there is a "window" of several

weeks during which Easter may be celebrated. By this reckoning, in

our calendar, Easter must occur between March 22 and April 25.

So, find the first day of spring in the northern hemisphere, or

the autumn equinox in the southern hemisphere, then find the first

full moon immediately following that. Easter will be the first

Sunday after (or on) that first full moon. Note the difference in

the southern hemisphere: Easter falls on the first Sunday on or

after the first full moon after the Autumnal equinox, not

after the first day of Autumn.

The system that was slowly developed throughout the Middle Ages

is the base for what we use today.

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