"The Time Has Come" (A Brief History of the Evolution of the Calendar)

January 2005 Meeting Report

Guest Speaker - Paul Roebuck


In a wide-ranging account of the evolution of our calendar, Dr Roebuck focused much of his attention on the changeover from the Julian to the Gregorian calendar. A year is the time it takes for the earth to complete one revolution around the sun. Since the time of Julius Caesar this had been calculated to be 365.25 days, provided for by making every fourth year a leap year, thus keeping dates more or less in line with the occur­rence of solstices and equinoxes, and therefore with the seasons. In fact, a revolution of the earth takes slightly less than 365.25 days, so that by the 16th century the discrepancy between solar and calendar time needed to be corrected.

To bring the two into line, Pope Gregory XIII decreed that the calendar should be changed in three ways. First, the number of leap years was slightly reduced by omitting them in three out of four centenary years. (In the Julian calendar, every year divisible by four is a leap year; the Gregorian differs in that a centenary is only a leap year if divisible by 400, so that there are three fewer leap years in every four centuries.) Second, the discrepancy that had accumulated since the introduction of the Julian calendar should be corrected by advancing the date by several days. Third, the start of year was changed from Lady Day (March 25) to January 1st.

Most Catholic countries in Europe adopted the Gregorian calendar in 1582, but Protestant countries refused to do so because they saw it as a popish proposal! Britain was one of the last to conform. It was not until 1751 that the Earl of Chesterfield (a local magnate who owned Shelford Manor) successfully introduced a bill into the British parliament incor­por­ating all three provisions of the Gregorian reform - though by then the discrepancy to be corrected had grown to eleven days. It came into force in September of the following year, when the 2nd was followed by the 14th; the first day of 1753 was to be January 1st, and the next centenary leap year would be 2000, thereby bringing the British calendar into line with that of most of the rest of Europe. Only one European country was later than Britain in making the change - Sweden.

These events explain some of the anomalies in our calendar today. In the Julian calendar, where March is the first month, September, October, November and December are the seventh, eighth, ninth and tenth months of the year, and derive their names from the Latin for these numbers. The names survived the 1752 change. Again, the start of our tax year on April 6th goes back to the time before 1752 when rents were normally paid on Lady Day (March 25); by advancing the date by eleven days, this brought it to April 6th.