Quand Georges Dieu crucifera
Que Marc le ressucitera
Et que Saint Jean le portera
La fin du monde arrivera.
French calendar riddle often erroneously attributed to Michel de Nostredame (1503-1566)
Also provided is a web page with an overview of the feast days in the Christian liturgical year and various other web pages comparing the dates of Easter according to different modes of calculation.
The Julian Easter reckoning was used generally up to 1582 when a modified algorithm was introduced with the Gregorian calendar reform. However, in many protestant countries the change to the Gregorian calendar and corrected Easter reckoning was not implemented until well into the 18th or even the 19th century. The Julian Easter reckoning is still employed by the Greek, Russian, Coptic and Ethiopian Orthodox churches.