Anomalous Easter Sunday Dates during the 18th and early 19th Century

On September 23, 1699 (O.S.), the German council of protestant theologians (Corpus Evangelicorum) at the Reichstag in Regensburg adopted a reform of the Julian calendar that was still employed in most of the protestant states in Germany. The new calendar, popularly known as the “Improved Calendar” (Verbesserte Calender), would be synchronized with the Gregorian calendar by deleting ten days between February 18 and March 1, 1700, and would be kept in step with the Gregorian calendar by adopting the same leap day rule.

However, there was a subtle difference in the Easter reckoning as, at the recommendation of the astronomer-mathematician Erhard Weigel (1625-1699) from Jena and advocated by his pupil Gottfried Wilhelm von Leibniz (1646-1716) and several other German astronomers and mathematicians, the date of Easter Sunday in the new calendar would no longer be derived from ecclesiastical tables (based on the mean motions of the Sun and the Moon) but from the astronomical times of the spring equinox and the following full moon. The astronomical calculations for determining these dates were to be based upon Johannes Kepler’s Tabulae Rudolphinae (1627) and the meridian of Tycho Brahe’s former observatory Uraniborg on Hven.

An additional provision – based on an erroneous interpretation of the acts of the First Council of Nicaea of 325 – stipulated that if the astronomical Easter Sunday happened to coincide with the first day of the Jewish Passover feast (Nisan 15), Easter would be postponed by a week to the next Sunday.

Proposals to adopt the modified calendar were also sent to the governments and heads of state of other European countries who still (partly or completely) employed the Julian calendar but only Denmark (which then also included present-day Norway), the Netherlands and the protestant cantons of Switzerland decided to adopt the German proposal.

As astronomers rapidly discovered, Easter Sunday dates calculated in this fashion would occasionally differ from the dates obtained from the Gregorian reckoning and that (without taking the Passover postponement rule into account) such occurrences would take place in 1700, 1724, 1744, 1778, 1798, 1802, 1805, 1818, etc. Already in the first year of the calendar reform (1700), the astronomical Easter Sunday would occur a week before the Gregorian Easter Sunday but as it would then coincide with the Jewish Passover feast it was postponed to the next week (thus coinciding with the Gregorian date).

Table of Astronomical Easters from 1700 to 1900

The following table lists all cases between 1700 and 1900 when the date of astronomical Easter Sunday differed from that calculated by the Gregorian Easter rules. The times for the spring equinox and the astronomical Full Moon are calculated from modern luni-solar ephemerides and are referred to the meridian of Tycho Brahe’s observatory Uraniborg (Hven), which was adopted to be 12º 42' (0h 50.8m) East of Greenwich.

Year Spring Equinox Astronomical Full Moon Easter Sunday Jewish
Passover
(Nisan 15)
Date h m Date h m Weekday Astron. Gregor.
1700 March 20 15 17 April   3 19 05 Saturday April   4 April 11 April   4
1724 March 20 10 59 April   8 16 21 Saturday April   9 April 16 April   8
1744 March 20 07 13 March 28 09 44 Saturday March 29 April   5 March 28
1778 March 20 13 12 April 11 21 10 Saturday April 12 April 19 April 12
1798 March 20 09 30 March 31 23 34 Saturday April   1 April   8 April   1
1802 March 21 08 39 April 18 03 27 Sunday April 25 April 18 April 17
1805 March 21 01 55 April 14 00 37 Sunday April 21 April 14 April 14
1818 March 21 05 41 March 22 14 59 Sunday March 29 March 22 April 21
1825 March 20 22 16 April   3 07 18 Sunday April 10 April   3 April   3
1829 March 20 21 33 April 19 07 12 Sunday April 26 April 19 April 18
1845 March 20 18 35 March 23 21 10 Sunday March 30 March 23 April 22
1876 March 20 07 01 April   8 20 30 Saturday April   9 April 16 April   9
1900 March 21 02 30 April 15 01 53 Sunday April 22 April 15 April 14

Note that in the years 1700, 1778, 1798 and 1876 (indicated with a different colour in the above table), the astronomically calculated dates of Easter Sunday fell on the first day of Jewish Passover (Nisan 15).

Anomalous Easter Sunday Dates observed in Protestant Europe

In 1724 and 1744, Easter was indeed celebrated a week earlier in the protestant regions of Germany, Switzerland (only in 1724) and Denmark. In the Netherlands, no one seems to have been aware of the fact that the astronomical Easter Sunday date could occasionally differ from the Gregorian Easter Sunday date and during the 18th century and afterwards Easter was always celebrated on the Gregorian dates.

In 1776, two years before the next anomalous astronomical Easter Sunday would occur (though the Passover postponement rule would have resulted in its coincidence with the Gregorian Easter Sunday), the protestant states of Germany finally agreed to adopt the Gregorian Easter reckoning. Together with the catholic states of Germany, who agreed to renounce the papal authorship of the calendar, both protestant as catholic communities in Germany henceforth observed the “Common Imperial Calendar” (Allgemeiner Reichs-Kalender) that in every detail was identical with the Gregorian calendar.

The following table lists the years between 1700 and 1845 when the “improved” Easter dates differed from the Gregorian Easter reckoning and the regions where these were observed.

Anomalous Easter Sunday dates observed in Protestant Europe
Year “Improved”
reckoning
Improved Easter reckoning observed in Gregorian
reckoning
Switzerland Germany Denmark Sweden Finland
1724 April   9 Yes Yes Yes April 16
1744 March 29 Yes Yes Yes(*) Yes(*) April   5
1802 April 25 Yes Yes April 18
1805 April 21 Yes Yes April 14
1818 March 29 Yes Yes March 22
1825 April 10 No Yes April   3
1829 April 26 No Yes April 19
1845 March 30 Yes March 23

(*) Reckoned as March 19 in the calendar of Sweden and Finland (for more details click here)


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