1583: Calendar reform

Ten days gone

The most interesting part of this little almanac is the first month of the calendar. What do we see? January has only 21 days! This is not a printer's error. Ten days have been intentionally eliminated. On 1 January the people of Holland went to bed and when they woke up the next day it was 12 January. The reason for this was a much discussed calendar reform.

Leap days

Our calendar originated with the Romans, whose year first consisted of 355 days. Under Julius Caesar the calendar was adapted to the solar year. The length of a year was set at 365 days, and every fourth a leap day was added. The solar year was fixed at 365.25 days. Actually, however, the year is a bit shorter: 365.2422 days - a small difference, perhaps, but after sixteen centuries the difference had swollen to ten days.

New calendar

The problem had already been recognized in the Middle Ages, but no one could agree on a solution. Finally the Italian physician Aloysius Lilius (c. 1510-1576) succeeded in producing a definitive design for the calendar reform, which was presented to Pope Gregory XIII after his death. A papal commission responded with a favourable decision, and on 24 February 1582 the papal bull Inter gravissimas was issued, announcing the new calendar. The vernal equinox, or aequinoctium (when day and night are of equal length), was set at 21 March. Before that, the vernal equinox had shifted back to 10 March. Because ten days had to be eliminated, Thursday 4 October of that year was immediately followed by Friday 15 October. To make sure the vernal equinox did not begin shifting again, it was decided to skip three leap days every 400 years. Only century years that are divisible by 400 would be leap years as well.

Netherlands

This calendar reform was not adopted throughout all of the Netherlands at the same time. Brabant and Zeeland immediately went ahead and skipped ten days in 1582. In those provinces, 25 December followed 14 December. Utrecht, Gelderland, Overijssel, Friesland and Groningen did not follow suit until 1700, and Drenthe in 1701.

Abroad

At first the Gregorian calendar was not accepted by other non-Catholic countries. England followed with a great deal of grumbling but not until 1752, Germany in 1776, Russia in 1918, and China finally agreed to go along with it in 1929. In the regions in which the new calendar had not yet been introduced, the two calendars were often used side by side. In such instances the abbreviations O.S. (old style / Julian calendar) and N.S. (new style / Gregorian calendar) were applied in almanacs in an effort to create order out of chaos.