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Calculating Easter

Thursday, 17 April, 2014

One of the most fascinating figures in the history of Easter is Nicholas of Cusa, a lawyer from Trier and a true Renaissance man, whose driving ambition propelled him all the way up from a non-noble birth to being made a cardinal by Pope Eugenius IV.

Nicholas established his reputation at the Council of Basel, which began in 1431 and went on for 18 years. He arrived in the Swiss town to argue the case of the disputed bishopric of Trier but made history by helping to broker an agreement in a bloody dispute between Rome and the Hussites. Then Nicholas turned to a matter that required enormous competence in law, mathematics and religious observance: the calendar. As John Mann writes in The Gutenberg Revolution:

Nicholas of Cusa “The Church was deeply concerned with the calendar because of the need to calculate the date of Easter. A thousand years before, the Council of Nicaea, laying out the ground rules of Christian practice, had decreed that Easter should fall on the Sunday following the full moon following the vernal equinox, one of two dates (in spring and autumn) on which day and night were of equal length. But the calendar of the time contained two errors. It’s year (365.25 days) was 11 minutes and 8 seconds too long, which over 1,000 years amounted to seven days; and the calculations that predicted the lunar cycle were way out as well. Actually, Roger Bacon, philosopher and scientist, had pointed this out seventy years before, but it was considered so intractable a problem that the papal authorities averted their eyes. In his De Reparatione Calendarii (On Revising the Calendar), presented to the Council in 1437, Nicholas expertly reviewed the evidence and proposed the only possible remedy: to adopt a new lunar cycle, leave out a week in the calendar — he suggested Whitsun, because it was a moveable feast and the general public wouldn’t notice — and then, as a final piece of fine tuning, omit a leap year every 304 years. This would have to be done not only with the agreement of the Greeks in Constantinople, because the were co-religionists, but also of the Jews, who would bear the brunt of revising all financial agreements.”

Given the fractured state of the church at the time, nothing was done, however. Reform had to wait for another 80 years when Pope Gregory XII introduced the “Gregorian” calendar, as we now know it. Still, the structure that measures our years and guarantees sweet indulgences in Spring owes an enormous debt to Nicholas of Cusa.

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