Unify and Fix the Date of Easter

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Easter is celebrated on a date that is fixed neither to a specific day of a month nor to a specific week in the civil calendar. Different creeds determine two different dates in most years. Reforming these two issues means, respectively, a fixation and a unification of the date of Easter. I petition all Christian churches to agree to do both, but at least do the latter, which most have committed to already. I also petition them to discuss this more openly and publicly.


Although there are apparently no written records of the meetings, it is generally agreed upon that the First Council of Nicaea, which took place in the year 0325, adopted a decree to determine the date of Easter independently from the Jewish calendar of the time. Pessach or Passover is on the 14th day of the lunar month of Nisan, which should be after the Spring equinox on the Northern hemisphere. The exact rules were either lost or not decided upon, but nowadays basically all Christians agree to celebrate Easter

  1. on a Sunday,
  2. after the vernal equinox (by varying definitions),
  3. after the Paschal full moon (by varying definitions), i.e. the first after the start of Northern spring,
  4. not together with Jewish Passover and, currently failing,
  5. all together on the same date.

Several feasts and holidays depend on the date of Easter and thus a lunar calendar, while many others are fixed within a solar calendar either by an ordinal day of a particular month or by a certain day of the week relative to such a date. Since early Christianity flourished mostly within the Roman Empire, its lunisolar calendar has been used almost exclusively for month-based dates. This is widely known as the Julian Calendar which has a leap day each and every fourth year. The Northern vernal equinox is assumed to fall on 21 March, but due to the inaccuracy of the Julian leap rule, this shifted over the centuries that followed. This was corrected by a new leap rule and realignment to the astronomic dates of the 4th century (i.e. the time of Nicaea) in the reforms issued by Pope Gregory XIII in 1582. This became to be known as the Gregorian Calendar, which is now the civil calendar in most countries and in all secular international matters. It is also used as the liturgical calendar of most Christian creeds, but many Orthodox churches stayed with the Julian calendar or a close equivalent, namely the Coptic calendar. This schism lead to two different methods to calculate the date of Easter, which currently only coincide in a about a third of all years. There have been several attempts to unify the date, especially within the World Council of Churches (WCC), which the Roman Catholic Church is not a member of, but Pope Francis has also publicly expressed a desire to finally solve this oecumenic issue and the Second Ecumenical Council of the Vatican (1962–1965) already approved any unanimous reform that did not break some fundamental principles like the continuity of the week cycle.

Available Options

There have been several suggestions and proposals for a common date of Easter. The following lists (using Gregorian dates and ISO 8601 rules for weeks) show the most prominent and some more exotic ones.

Arithmetic rules approximating observed astronomy

  • Catholic / Western / Gregorian Computus:
    22 Mar ‥ 25 Apr
  • Orthodox / Eastern / “Julian” Computus:
    4 Apr ‥ 8 May

Astronomic rules (as observed from Jerusalem)

  • 1st Sunday after the 1st full moon
    • after the Northern vernal equinox:
      21 Mar ‥ 24 Apr (Revised Julian, Constantinople 1923)
    • after the day of the Northern vernal equinox:
      22 Mar ‥ 25 Apr (WCC, Aleppo 1997)
    • after the sunset after the Northern vernal equinox
    • after the sunrise after the Northern vernal equinox
  • 1st Sunday after the sunset after the 1st full moon
    • after the Northern vernal equinox
    • after the sunset after the Northern vernal equinox
  • 1st Sunday sunrise after the 1st full moon
    • after the Northern vernal equinox
    • after the sunrise after the Northern vernal equinox
    • after the sunset after the Northern vernal equinox

Calendric rules

  • Sunday of the 14th week of the year (W14-7):
    4‥11 April (e.g. Symmetry 454, 2004)
  • Sunday of the 1st full week in April:
    7‥13 April
  • 2nd Sunday in April:
    8‥14 April (e.g. Pope Tawardos II, 2014)
  • 15th Sunday of the year:
    8‥15 April
  • Sunday after the 2nd Saturday in April:
    9‥15 April (e.g. UK Parliament, 1928)
  • Sunday of the 2nd week in April 
    (i.e. Maundy Thursday = 2nd of the month):
    11‥17 April
  • Sunday of the 15th week of the year (W15-7)
    (i.e. Maundy Thursday = 15th of the year):
    11‥18 April
  • 3rd Sunday in April:
    15‥21 April (e.g. Archbishop Welby, 2016)

All calendric proposals above yield dates between the earliest Orthodox date (4 Apr until 2100) and the latest Catholic date (25 Apr). All alternatives that cover 9 April as a possible date for Easter Sunday agree on this very date in the year 2034, which makes it a good time and realistic goal to adopt one of them.

Due to a lack of public records of WCC meetings and other summits, it remains unclear which of these alternatives are favored by or acceptable to whom.

Purely astronomic rules have reached the widest committee consensus historically, but have failed to be implemented anywhere. They are also not popular with most civil authorities and businesses, because holidays fixed to a specific day or week in the civil calendar simplify annual scheduling and accounting.

The Gregorian calendar better approximates astronomic reality than the Julian, thus the only reason for Orthodox churches to stay with the latter is tradition. However, it might make it easier for Eastern churches to agree on a reform if the Western churches would be affected to a similar degree by the change. A fixed date would achieve that.

While international standards, ISO 8601 in particular, have agreed to begin the week on Monday, Christian tradition has it start on Sunday. Nevertheless, all feasts that are celebrated on a particular day of the week could also be fixed within canonical calendar weeks.

Since Passover (Passa, Pessach) is on the 14th day of Nisan in the Hebrew calendar, a fixed date that is the 14th day of a month (“Christian Nisan”) in an alternative calendar may be appealing. This is equivalent to the 2nd Sunday in months that consist of a whole number (i.e. 4 or 5) of weeks that start on Monday. Out of the proposed rules listed above, the following would qualify:

  • Sunday of the 14th week of the year (W14-7) 
    = 14th day of the 4th of 13 4-week months 
    (cf. Eastman/Cotsworth plan)
  • Sunday of the 2nd week in April 
    = 14th day of “week-April”
  • Sunday of the 15th week of the year (W15-7)
    = 14th day of 2nd 13-week quarter
    (divisible into 3 months, cf. early-Christian Enoch/Qumran calendar)