Holidays related to Easter: Difference between revisions

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 in parallel to our standard purely-solar one.

When Pope Gregory reformed the Catholic calendar in 1582 CE, the drifting of Easter with respect to the seasons was the driving motivation, and the rules for determining it were altered to correct that drift. Catholic nations adopted both setsthe ofnew changescalendar and the new Easter rules right away, while Western Protestant nations adopted them more gradually over the next 350 years or so. Eventually, even nations dominated by the Eastern Orthodox church adopted a similar calendar reform for civil use (the Revised Julian calendar), so pretty much the whole world agrees on what day it is for civil purposes. However,But the Eastern Churchchurches never adopted the corresponding Easter rule changes-; they still usesuse the original Julian calendar and rules to determine the datesdate ofknown majorin Christianthe holidays,West includingas "Eastern Orthodox Easter". SoTherefore, 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.

In the year 400 CE, Easter Sunday iswas April 1st, making Ascension Thursday May 10th and Pentecost May 20th. It is ahistorical to give a date so far back for either Trinity Sunday or Corpus Christi, neither of which were observed until centuries later, but they would have been May 27th and 31st.

Skipping forward to the year 2100 CE, assuming the rules don't change between now and then, the Western churches will observe Easter on March 28, Ascension Thursday May 6th, Pentecost May 16th, Trinity Sunday May 23rd and Corpus Christi May 27th. Heading East, the Orthodox rules place Easter on April 18 that year, but that's in the original Julian calendar; the Gregoriancorresponding or Revised Juliancivil date is May 2nd. That puts the Ascension on June 10th and Pentecost June 20th. Orthodox Trinity Sunday is the same day as Pentecost, so that's still June 20th, while Corpus Christi is a purely Catholic date that has no Orthodox version.