The date of Easter varies from year to year. It occurs on the first Sunday after the first full moon on or after 21 March, a date taken, in accordance with an ancient ecclesiastical tradition, to be that of the spring equinox, but which does not always correspond to the astronomical equinox. The Julian Calendar is taken as the basis of the calculations by nearly all Oriental Orthodox and Eastern Orthodox Churches and is accepted even by Latin Church Catholics in countries such as Ethiopia and Greece. In the 20th and 21st centuries, the Julian Calendar's 21 March corresponds to 3 April in the Gregorian Calendar, the calendar used for civil purposes in most countries. The earliest possible date for Easter is 22 March, and the latest 25 April. These dates in the Julian Calendar now correspond to the Gregorian Calendar's 4 April and 8 May.