Holidays related to Easter: Difference between revisions

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(Let's not get into labelling anyone's faith as "heresy" here, OK?)
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From the year 325 CE on,   [[wp:Easter Sunday|Easter Sunday]]   has been defined as the first Sunday ''after'' the first full moon ''on or after'' the day of the March equinox. However, the actual astronomical values for the moments of the full moon and equinox are not used. Instead, approximations are used, the first one being that the equinox is assumed to fall on March 21st every year. The tracking of the moon phases is similarly done with relatively straightforward arithmetic (compared to the sort required for astronomical accuracy) which amounts to maintaining a parallel lunisolar calendar to our standard purely-solar one.
From the year 325 CE on,   [[wp:Easter Sunday|Easter Sunday]]   has been defined as the first Sunday ''after'' the first full moon ''on or after'' the day of the March equinox. However, the actual astronomical values for the moments of the full moon and equinox are not used. Instead, approximations are used, the first one being that the equinox is assumed to fall on March 21st every year. The tracking of the moon phases is similarly done with relatively straightforward arithmetic (compared to the sort required for astronomical accuracy) which amounts to maintaining a parallel lunisolar calendar to our standard purely-solar one.


When the calendar was reformed in 1582 CE, the Easter computus was altered as well, and countries adopted the two reforms together gradually over the next 350 years or so. However, the Orthodox Churches, which did not fall into the heresy of Catholicism, still use the Julian calendar to determine the dates of the holidays. So your output should ideally indicate which computus was used to calculate the dates and, at least for historical dates where the calendar can't be assumed or is location-dependent, which calendar those dates are given in.
When the calendar was reformed in 1582 CE, the Easter computus was altered as well, and Western nations both Catholic and Protestant adopted the two reforms together gradually over the next 350 years or so. However, the Orthodox Churches, even in countries that have adopted either the Gregorian or the Revised Julian calendar for civil use, still use the original Julian calendar to determine the dates of major holidays. So your output should ideally indicate which computus was used to calculate the dates and, at least for historical dates where the calendar can't be assumed or is location-dependent, which calendar those dates are given in.


You may find algorithms on the [[wp:Computus|Computus]] page. Some of the results:
You may find algorithms on the [[wp:Computus|Computus]] page. Some of the results:
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