Catholic : In the year 325, the Council of Nicée determined a date fo Easter. Full Moon would fall the 14th day of a moon month (1). Easter would be marked by the dominical letter(2)and the epactus(3). With the establishment of the equinox ne variatur on March 21, algorithms where elaborated to attribuate a date for Easter whatever the year.
Time between two consecutive new moons: 20 days 12 hours 44 minutes 2.8 - Gives a letter code for the year's calendar Age of the moon on January 1st, minus one unity, 0 being the new moon's age.