Growing up I was always frustrated that Easter was always on different days of the year. In contrast to Christmas or Thanksgiving, Easter always seemed to change. Sometimes it was in March, sometimes in was in April. How is one to make sense of it all?
There is actually a method of behind the madness. And the method goes back a long time into history. If you compare all of the possible dates for Easter, you will observe that Easter can occur on any Sunday March 22 through April 25. Why between those dates?
Easter and the Council of Nicaea
It can be traced back to 325 AD, when the Council of Nicaea decreed that Easter was to be celebrated on the first Sunday after the first full moon after the spring equinox (which falls on March 21).
The reason the Council of Nicaea took up the issue, was because during the first couple centuries many churches would celebrate the Resurrection on the Sunday closest to the Jewish Passover. However, the problem was that sometimes there was disagreement between the two closest Sundays in question. Furthermore, some churches would celebrate Easter on the Passover, even if it was not on a Sunday.
Misguided in large part by nascent antisemitic motives, the Council of Nicaea sought to create further separation between Christianity and Judaism. Hence, the council decreed that Easter must always fall on a Sunday, the first after the full moon after March 21. Thus, the first day Easter could hypothetically be would be March 22 (last time that happened was 1818).
So, in summary, the formula for determining the date for the Easter celebration is as follows:
Date of Easter = 1st Sunday after 1st Full Moon after March 21st
Now you can impress your friends with this knowledge! Or, perhaps better yet, you can know when to celebrate the amazing reality that Jesus Christ has risen from the dead as the firstfruits of those who will be raised in the future! Happy Easter!
For more on the subject, see the entry in Encyclopedia Britannica.