In 725, Bede succinctly wrote, "The Sunday following the full Moon which falls on or after the equinox will give the lawful Easter." However, this does not precisely reflect the ecclesiastical rules. The full moon referred to (called the Paschal full moon) is not an astronomical full moon, but the 14th day of a lunar month. Another difference is that the astronomical equinox is a natural astronomical phenomenon, which can fall on 19, 20 or 21 March, while the ecclesiastical date is fixed by convention on 21 March.