CALENDAR AND ASTRONOMY

The Gregorian calendar dates back to 1582. It was, in fact, at this time that Pope Gregory XIII replaced the Julian calendar established forty-seven years before Christ by Julius Caesar.

The Julian calendar also had leap years. On the instructions of the astronomers Eudote and Sosigenes, the Latin emperor wanted to remedy the defect of a numeration based on a year of three hundred and sixty-five days, too short by almost six hours. We therefore added twenty-four hours, or one day, to one year out of four.

But we then encountered another drawback if three hundred and sixty-five days were not enough to number the rotation of the earth around the sun, three hundred and sixty-five and a quarter days, on the other hand, slightly exceeded the goal.

The Julian almanac therefore delayed by a fraction of a day each year. This explains why the Russian year, which has remained the Julian year, is today approximately fifteen days behind the Gregorian year.

Pope Gregory XIII retained leap years as in the Julian calendar. But to avoid the delay that we have just pointed out, and to bring the calendar and astronomical truth into agreement as much as possible, he removed three days every four centuries. This is how the secular year, that is to say the one which ends the century, is a leap year when the number of hundreds is divisible by four - 1900 was not a leap year, the year 2000 will be.

Despite this, there is no absolute concordance; there still remains a slight gap, but neither you nor I, of course, will suffer from it: it does not reach twenty-four hours for more than four thousand years!