How Is Easter Determined?
Easter falls on a Sunday between 22 March and 25 April, but working out which Sunday exactly requires an astronomical calculation. The simple standard definition of Easter is that it is the first Sunday after the full Moon that occurs on or dating the spring equinox. If the full Moon falls on a Sunday then Easter is the next Sunday.
Up to the 8th century AD, there was no uniform method for determining the date of Easter, but the method favoured by the Council of Nicaea in AD gradually became the accepted method.
Earliest Easter
The adoption of the Gregorian calendar requires some modifications to easter scheme but it is still basically easter same. Unfortunately this simple definition is not strictly speaking correct. The spring or vernal equinox used is click the following article the true equinox but an artificial one always assumed to be on 21 March.
The full Moon used is not the true full Moon but an artificial construct based on the Metonic cycle below. The reasons for this are that the method is then independent of longitude on the Earth and is thus independent of time zone. It also allows the date of Easter dating be calculated in advance regardless of the actual motion of the Earth around easter Sun.
The method quoted here is valid for the determination of the date of Easter in Western Christian churches; the date used by the Eastern churches can be one, four or five weeks later. The Metonic cycle of 19 years is one in which the phases nola speed dating the Moon repeat exactly.
Astronomical vs. Ecclesiastical Dates
It is thus possible to have a year cycle for the dates of full or new Moon. In the Julian calendar this year cycle can be fairly easily translated dating a date for Easter. These leap years mess up the simple Metonic cycle by altering the number of days in different periods of 19 years. An algorithm to find the date of Easter which is valid from to has been derived by Carter as follows:.
Calculating the Easter Date
If Q is less than 32 then Easter is in March. If Q is greater than 31 then Q - 31 is its date in April. Keep track of time with Royal Observatory Greenwich watches, and our famous Shepherd Gate clock, reproduced for your wall at home.
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