Standardization of Easter Celebration Date
The Catholic Church fixes the date of Easter, its celebration to mark the resurrection of Christ, using a method set out in AD 325 by the Council of Nicaea. In the first centuries AD, Easter was celebrated on different days by different groups of Christians, the Council of Nicaea sought to standardize it.
Role of Full Moon
Easter is now celebrated on the first Sunday after the full moon occurring on or after the spring equinox. Early Christians couldn’t simply wait to find out when the full moon would fall, then quickly celebrate Easter. They had to fit in Lent – 40 days of fasting – immediately beforehand, so had to know several weeks in advance when that full moon would fall, a task that could only be achieved by keeping astronomical records and projecting into the future.