Easter is one of the most significant dates on our calendar every year. However, unlike many other holidays that have a fixed date, Easter's observance can vary widely from year to year, falling on any Sunday between March 22 and April 25. This variability has puzzled many, leading to the question: Why does Easter fall on a different day each year?
The answer lies in the sky, specifically in the movements of the moon and the sun. Easter is scheduled to fall on the first Sunday after the Paschal Full Moon, which is the first full moon occurring on or after the spring equinox. However, the determination of the Paschal Full Moon is not based on actual astronomical observations but on a set of ecclesiastical rules and tables, which approximate the lunar cycle.
This system was established by the Council of Nicaea in A.D. 325, with the aim of harmonizing the celebration of Easter among Christians. The council's decision to link Easter to the Paschal Full Moon and the spring equinox was a compromise between following a purely lunar calendar, like the Jewish calendar used to determine the date of Passover, and a fixed solar date.
The ecclesiastical rules that define the date of Easter add even more complexion. For instance, the church calendar fixes the date of the spring equinox on March 21, regardless of the astronomical equinox's actual date. Additionally, the methods for calculating the Paschal Full Moon vary, leading to differences in Easter dates between the Western (Roman Catholic and Protestant) and Eastern (Orthodox) Christian traditions.
Despite the complexity behind the date of Easter, its variable nature has a beautiful underlying significance: our celebration of Jesus' resurrection aligns with the cycles of rebirth and renewal amongst God's creation.