Calendopaedia - The John Dee Calendar

Dr. John Dee (1527 1609) was a well known (in his time) scientist, mathematician, astronomer and astrologer. He was a member of the court of Queen Elizabeth I of England and had advised the Queen on various matters in the past. He was well read and collected books on a variety of subjects. His personal library was believed to be one of the largest in the country.


The Julian calendar was in use around the world at this time but was known to be inaccurate. It had been adopted by the Roman Catholic Church at the Council of Nicaea in AD 325. In order to correct the problems with the Julian calendar Pope Gregory XIII proposed the adoption of the Gregorian calendar which was approved by the Council of Trent (1545-1563). This proposal was enforced by a papal bull, issued in 1582, that it should be adopted by all churches and all countries. However the church in England had separated from the church of Rome in 1534 during the reign of King Henry VIII. The Anglican bishops and the Queen refused to be ordered about by the Pope and wished to show their independence, so they were reluctant to implement the new calendar.

Sir Francis Walsingham proposed that John Dee be asked to look into the issue of improving the calendar without using the Gregorian calendar. He thoroughly investigated the problem and produced a report explaining his thoughts and his proposal of a new calendar. The report ran to 62 pages and was delivered on 26 February 1583. This report was entitled "A playne Discourse and humble Advise for our Gratious Queen Elizabeth, her most Excellent Majestie to peruse and consider, as concerning the needful Reformation of the Vulgar Kalendar for the civile years and daies accompting, or verifyeng, according to the time truely spent." which is often abbreviated to "A playne Discourse". It is thought that the original document has been lost but there are at least two copies, hand-written in the same era, at the Bodleian Library in Oxford.

John Dee's Calendar

The calendar that Dr. Dee proposed was based on the days and months of the Gregorian calendar but the arrangement for leap years was different. The Gregorian calendar has a four hundred year cycle, that is 400 years must elapse before the leap years fall in exactly the same pattern. Dee's calendar has a cycle of only 33 years. During the 33 year cycle there are eight leap years. The leap years are every fourth year, that is years 4, 8, 12, 16, 20, 24, 28 and 32. This simple rule is actually more accurate than the Gregorian calendar, which has an average year length of 365.2425 whilst Dee's calendar has an average year length of 365.2424. The current year length between vernal equinoxes is 365.24238 days.

Dee's Proposed Transition

Pope Gregory's Papal Bull stated that ten days should be dropped to bring Easter back to the time it was at the Council of Nicaea (AD 325). Dee proposed that eleven days be dropped to bring the calendar back to the position it would have been in at the time of Christ. This does seem a more sensible suggestion. He also proposed that the days should not be dropped all in one go but two or three days at a time by shortening the months of May to September.

Attempts were made to convince other protestant countries to adopt Dee's calendar but none would commit to it. Traders complained that they would be out of step with Europe and the Anglican Bishops found it hard to agree on whether it was better than following Rome, or not. In the end no decision was made and Britain waited until 1752 and then adopted the Gregorian calendar. Because of the delay of almost 200 years it was necessary to drop 11 days just to align with the Gregorian calendar.

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