A New Year’s Toast To Pope Gregory XIII

by Tim Thompson

Today, most of the world celebrates New Year. But that has been the case only since the adoption of the Gregorian calendar, which began to replace the older Julian calendar in 1582. The process lasted from 1582 until 1929, when the Soviet Union became the last country to abandon the Julian calendar (Greece switched in 1923). Most of the Catholic countries reformed their calendars quickly, in 1582-1583, while the non-Catholic countries followed rather slowly.

The British Empire and its colonies did not switch until 1752, well after most of the Founding Fathers of the USA were born, so it is necessary to distinguish between “old style” (Julian) and “new style” (Gregorian) dates in American history. For instance, we recognize George Washington’s birthday as 22 February 1732, but he was born on 11 February 1732, when the Julian calendar was in place; 22 February is the translation of the Julian date into the Gregorian date, pretending that the Gregorian calendar had been in force even in 1732.


The Gregorian calendar was adopted on the authority of Pope Gregory XIII [1502-1585], in order to fix the date for Easter, and return it to a date near the spring equinox (northern hemisphere), as it had been set in the First Council of Nicaea (20 May – 19 June, 325). The need to move Easter back to the right place in the calendar meant that when the new Gregorian calendar was adopted, 11 days were dropped, so that the day after Julian Thursday 4 October 1582 was Gregorian 15 october 1582 (5-14 October vanished).

Another big change was that the beginning of the new year moved from 1 March to 1 January. Leap day at the end of February was the last day of the year on the Julian calendar; leap day remained at the end of February, but now it seems incongruous, since there is nothing otherwise special about the end of February in the Gregorian calendar.

First page of the papal bull Inter Gravissimas. Click to enlarge.

First page of the papal bull Inter Gravissimas. Click to enlarge.

The old Julian calendar had been established in 46 BC under the authority of legendary Roman Emperor Julius Caesar [100-44 BC]. It was a modification of the older (and already many times reformed) Roman calendar. In even older, ancient civil calendars, the seasons were not fixed (i.e., the equinox and solstice dates drifted from year to year). The Roman calendar had already fixed that problem, but in a very cumbersome way. The old Roman calendar had 12 months, but only 355 days, so the Romans adopted leap months instead of leap days, and some years were as long as 378 days, just to keep the seasons in line. The Julian calendar fixed that, and fixed the length of the average year at 365.25 days.

But the real year is about 365.2425 days (a fact already known to ancient Greeks, but ignored by Caesar). So the seasons slowly slipped, and by 1582, had drifted about 11 days out of sync. Hence, the adoption of the Gregorian calendar included slipping the calendar back to compensate. Also, the Gregorian calendar changes the rule for leap years, so that century years are leap years only if they are evenly divisible by 400. So, 1700, 1800 and 1900 are not leap years, but 2000 is (and 2100 will not be). This small difference is enough to keep the civil calendar in sync with the seasons for about 10,000 years.

The Julian calendar and the older Roman calendars all started the new year in 1 January beginning about 153 BC. But in post-Roman Europe, the new year was usually moved to a date of Christian importance, such as Easter, the date of Annunciation (25 March) or the Nativity (25 December).

In post-Roman Anglo-Saxon England, the new year commonly began on 25 December, to align with both the pagan Winter Solstice and the Christian Nativity. When the Normans took over, they moved the new year to 1 January (1087-1155), then moved it to 25 March (1155-1751). In 1752, when the British Empire finally adopted the Gregorian calendar, New Year once again moved to 1 January.

So you can thank Pope Gregory XIII (and the British Empire) for today being New Year.


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