Friday, October 3, 2014

Pope Kills Ten Days

Tomorrow is the fourth of October, imagine going to bed in the evening and the following morning you wake to find that it is not the fifth but the fifteenth of the month; ten days have gone missing. This is exactly what happened in 1582. In accordance with a proclamation by Pope Gregory XIII, the day after Thursday, 4 October, was Friday, 15 October. For the Roman Catholic world, the intervening ten days were removed from the calendar and never took place. 

The reason for this calendrical sleight of hand had to do with leap years and with Easter. Adding a day to the end of February every fourth year worked well to keep the calendar aligned with the astronomical year. But the calendar was slightly too long by a few minutes each year. Over the centuries, this creepage in was causing each successive Easter to fall a little earlier in the season. 

The seasons cycle from spring to summer to autumn to winter and back again. Think of this annual cycle as the top of a cup or drinking glass. Divide the rim into equal quadrants, one for each season. We can think of the calendar as a strip of paper. 365¼ days worth of paper wraps around the glass, but overlaps by a very small amount. In this way, each year the calendar begins a few minutes later in the season than the previous one.

The leap year system was devised in the Roman Empire and it served admirably for many centuries. However, owing to some errors in calculating early leap years and the slight error accumulating year after year over a millennium and a half 1200 years,[1] the calendar had advanced in the seasons by about ten days. Because the date of Easter is calculated astronomically, it falls within a fixed range on the rim of our glass, but the calendar kept inching forward and Easter was falling in early March, which was not acceptable to the Church. Various gradual measures were considered to remedy the situation, but in the end, it was decided to make up for the discrepancy all at once; the ten extra days accumulated over the millennium were deleted from the calendar. In addition, new rules were added for 'leap centuries'. This effectively fixed the problem.[2]

Other parts of Europe eventually adopted the changes, some sooner than others. In France, 9 December 1582 was followed by 20 December. A letter sent from Italy on November first of that year might well appear at its destination in France the last week of October, seeming to arrive before it was sent. In the Netherlands and Germany some provinces made the changes while others held out until 1700. Protestant countries did not generally adopt the new system until much later. Britain and her American colonies did not make the change until 1752 by which time the calendars were out of synchronization by a full eleven days.

When the Calendar was adjusted in Italy, Antonio Neri was six and a half years old; hardly old enough to remember the event. However, he must have experienced some of the stranger side effects in his adult life, especially when traveling. In making the journey to visit Emmanuel Ximenes, in Antwerp in 1604, if our priest stuck to the route suggested by his friend, he would have remained in Catholic territory until the very end of his journey. Once in the Low Countries, the date of the month would depend on the city. In Protestant controlled regions, like Utrecht, the date would suddenly jump backwards by ten days from nearby Catholic regions, although the days of the week would be consistent. Those crossing the English channel, from Calais France to Dover, for example, would experience a similar effect; it might be early May on one side and late April on the other. In such a crossing, one would experience the disconcerting 'Déjà vu' of living the same date range twice, once as Monday through Friday and then again as the following Thursday through Monday.

If there is a lesson here for close observers of nature, it is that daily living in the early seventeenth century emphasized the difference between the natural world and the contrivances of man. Subtle as it may seem to us today, April does not so much signify the rebirth of our gardens, as the rebirth of our gardens is what we have come to call April. The realignment of the calendar in 1582 emphasized this distinction, foreshadowing philosopher-scientist Alfred Korzybski's premise that "the map is not the territory."

[1] The Catholic Julian Calendar dates from the council of Nicaea in 325 CE, as kindly pointed out by Thony Christie (, Thanks!

[2] The authoritative reference on the full extent of the changes and the events leading to them is Coyne, Hoskin, Pedersen 1983. (See the 'bibliography' link to the right.)

This post first appeared in a different form on 23 September 2013.

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