I thought I thoroughly understood the method the Church used to determine the date of Easter: the first Sunday after the first Full Moon after the Spring Equinox. Simple and easy but I should have known it was way more complicated. This is how it actually works, according to the Jesuit papal astronomer, Guy Consolmango. It all started with an understandable, natural method devised by God and of course, they complicated it all to hell and gone. For the Roman Catholic Church isn’t satisfied until they got their priestly elites involved to nicely obfuscate everything, damn them.
The system finally adopted for determining the date of the New Moon was worked out some 200 years later by Dionysius Exiguus, a monk who lived in Rome in the first half of the 6th century. In the process, he introduced the concept and numbering of the “Anno Domini” years now in common use.
Dionysius constructed a table that allowed one to read off the date of the New Moon for each month of every Julian year in the 19 year Metonic cycle; this table was repeated every 19 years. The first cycle was said to commence with the year AD 1. A Golden Number was defined as the value that indicated where the current year sat in the Metonic cycle of the Old Testament defining Passover (and thus Easter) in the following mode: one would celebrate Easter on the Sunday that followed the first full Moon after the 21st of March. If the full Moon itself fell on a Sunday, Easter would be celebrated on the following Sunday. This was to avoid the confusion of the Christian Easter with the Hebrew Passover.
Thus, to compute the date of Easter of any given year, one first determined the Golden Number of the year; then, in Dionysius’ table of New Moons, one looked for the first New Moon after March 21. The Paschal Moon, the Full Moon, would occur 13 days later, that is, on the 14th day of the lunar month.
The date of Easter would be the Sunday after this Full Moon unless this Full Moon fell on a Sunday; in that case, Easter would be celebrated on the following Sunday. (Knowing which day was Sunday for any given month of any given year could also be computed easily with further tables provided by Dionysius. The sequence of the days of the week continued uninterrupted through all of these calendar reforms.) Thanks to these New Moon tables, the date of Easter could be computed without ambiguity.
The Pascal New Moon would occur between 8 March and 5 April, and so the Full Moon could occur from 21 March to 18 April. Given the possibility that 18 April itself might be a Sunday, the dates on which Easter could occur thus ranged from 22 March until 25 April. Recall that for the ancient Hebrews, Passover was always fixed on the 14th day of the first month of the year, i.e. the day when the Full Moon actually occurs. For them, the date could be determined without needing to use any complicated, approximate tables; anyone can see the Full Moon, which was what was particularly important to them for determining holy days. For the Christian Easter, however, this no longer held; indeed, Easter could occur as much as seven days after the Full Moon.