Christmas? Easy! Always on the 25th of December in the States, 24th in Europe. But when in the heck is Easter?
When is Easter? (Short answer)
Easter Sunday is the first Sunday after the first full moon after vernal equinox.
When is Easter? (Long answer)
The calculation of Easter is complicated because it is linked to (an inaccurate version of) the Hebrew calendar. Jesus was crucified immediately before the Jewish Passover, which is a celebration of the Exodus from Egypt under Moses. Celebration of Passover started on the 15th day of the (spring) month of Nisan. Jewish months start when the moon is new, therefore the 15th day of the month must be immediately after a full moon. It was therefore decided to make Easter Sunday the first Sunday after the first full moon after vernal equinox. Or more precisely: Easter Sunday is the first Sunday after the "official" full moon on or after the "official" vernal equinox. The official vernal equinox is always 21 March. The official full moon may differ from the real full moon by one or two days. (Note, however, that historically, some countries have used the real (astronomical) full moon instead of the official one when calculating Easter. This was the case, for example, of the German Protestant states, which used the astronomical full moon in the years 1700-1776. A similar practice was used in Sweden in the years 1740-1844 and in Denmark in the 1700s.) The full moon that precedes Easter is called the Paschal full moon.
Two concepts play an important role when calculating the Paschal full moon: The Golden Number and the Epact. They are described in the following sections. The following sections give details about how to calculate the date for Easter. Note, however, that while the Julian calendar was in use, it was customary to use tables rather than calculations to determine Easter. The following sections do mention how to calculate Easter under the Julian calendar, but the reader should be aware that this is an attempt to express in formulas what was originally expressed in tables. The formulas can be taken as a good indication of when Easter was celebrated in the Western Church from approximately the 6th century.
There you have it!
When is Easter? (Short answer)
Easter Sunday is the first Sunday after the first full moon after vernal equinox.
When is Easter? (Long answer)
The calculation of Easter is complicated because it is linked to (an inaccurate version of) the Hebrew calendar. Jesus was crucified immediately before the Jewish Passover, which is a celebration of the Exodus from Egypt under Moses. Celebration of Passover started on the 15th day of the (spring) month of Nisan. Jewish months start when the moon is new, therefore the 15th day of the month must be immediately after a full moon. It was therefore decided to make Easter Sunday the first Sunday after the first full moon after vernal equinox. Or more precisely: Easter Sunday is the first Sunday after the "official" full moon on or after the "official" vernal equinox. The official vernal equinox is always 21 March. The official full moon may differ from the real full moon by one or two days. (Note, however, that historically, some countries have used the real (astronomical) full moon instead of the official one when calculating Easter. This was the case, for example, of the German Protestant states, which used the astronomical full moon in the years 1700-1776. A similar practice was used in Sweden in the years 1740-1844 and in Denmark in the 1700s.) The full moon that precedes Easter is called the Paschal full moon.
Two concepts play an important role when calculating the Paschal full moon: The Golden Number and the Epact. They are described in the following sections. The following sections give details about how to calculate the date for Easter. Note, however, that while the Julian calendar was in use, it was customary to use tables rather than calculations to determine Easter. The following sections do mention how to calculate Easter under the Julian calendar, but the reader should be aware that this is an attempt to express in formulas what was originally expressed in tables. The formulas can be taken as a good indication of when Easter was celebrated in the Western Church from approximately the 6th century.
There you have it!
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