Anomalous Easter Sunday Dates in 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 (15 Nisan), 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 which 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 12° 42' (0h 50.8m) East of Greenwich.

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

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

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

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