Spring : equinox, easter date

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Spring : Spring equinox, Easter date

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Spring equinox occurs every year on the 20th or the 21st of march (20th of march in 2002). On this date, the earth axis is inclined from the left to the right in comparison with the sun axis ; the projection circle of the sunlight onto the earth thus passes by both poles and day is equal to nigth (equinox="equal nigth").

YEAR		Easter date, in the Catholic Church (the date for our european calendar), contrary to common opinion, is not fixed to the Sunday after the first full moon after the spring equinox. According to the Council of Nicée (325), it takes place on the 1st Sunday after the first ecclesiastic full moon after the 21st of march or coinciding with this date. The difference may reach several days because the equinox occurs on the 20th or the 21st of March and the ecclesiastic moon calendar, determined from tables, is an approximation of astronomic moon calendar.

Easter day can only be worked out by complex calculations bringing into play multiple adjustments. So the above calculator is only valid between 1583 (the year after the institution of the Gregorian calendar) and 4100 when the adjustments become uncertain. Moreover all could be changed quite before that, because discussions are under way between the Christian Churches in order to unify this date.