The ancient Chinese and Greeks discovered that the Earth takes 365 days, 5 hours, 48 minutes and 46 minutes to revolve around the sun. Since the extra hours and minutes make an awkward fraction, complicated calendars which had extra months included in every 19-year cycle were produced. In 45AD, Julius Ceasar’s astronomer, Sosigenes discovered that all Roman festivals had got out of line with the seasons of the year, and to rectify the situation, he recommended that the year 45AD be prolonged to 445 days. A recommendation that Ceasar followed. Thereafter, Sosigenes developed the Julian (named after Ceasar) Calender by approximating a year to be 365 and a quarter days. In the calender, a year was defined as having 365 days and a leap day added every four years to compensate for the lost quarter day.
In 730AD, the Venerable Bede, a mathematically skilled Anglo-Saxon monk, pointed out that the 365 1/4-day Julian year was 11 minutes, 14 seconds too long. But since the error added up so slowly (the calendar fell out of sync with the sun by only a day every 128 years) no one did anything about it. In 1582. Pope Gregory XIII noticed that the spring equinox – when day and night are of equal length – fell upon March 11 instead of March 21. The pope fixed the problem by erasing 10 days, declaring that the day following Oct. 4, 1582 would be known as Oct. 15, 1583. To make the calendar more sun-accurate than Caesar’s, Pope Gregory XIII pulled out his abacus and came up with the following criteria to determine leap years:
- Every year that is evenly divisible by four is a leap year;
- of those years, if it can be evenly divided by 100, it is NOT a leap year, unless
- the year is evenly divisible by 400. Then it is a leap year.
Pope Gregory XIII’s calender was called the Gregorian Calender. It was not so popular at first though. The Roman Catholic nations such as Italy, Poland, Portugal and Spain adopted it with ease, but protestant nations were reluctant. When it was finally adopted in Britain (and America) in September 1752 by the loss of 11 days, there were wide protests around the country. Sweden (and Finland) adopted it in 1712 by adding two “double” leap year in 1712. Two days were added to February–creating a date of February 30, 1712. (This was done because the leap year in 1700 was dropped and Sweden’s calendar was not synchronized with any other calendar. By adding an extra day in 1712, they were back on the Julian calendar. Russia didn’t accept the Gregorian calendar until 1918, which means that when the U.S. purchased Alaska in 1867, 11 days were lost in the transition from the Julian calendar. Leap years are also significant for Alaskans because summer solstice (when the Earth’s axial tilt is inclined towards the sun at its maximum of 23° 26′.) occurs about 18 hours earlier in a leap year.
Even this system is not entirely correct. Every 10,000 years the Gregorian calendar becomes two days, 14 hours and 24 minutes in error. If we last long enough, adjustments will be necessary. One suggestion has been to make a further leap year refinement – excluding leap days from years divisible by 4000. Another suggestion, particularly popular between the two world wars, was for a new world calendar. At the moment Muslims have their own calender in which a year ends after every 12 lunar months. There are also at least 17 different calendars in India and Africa. But the problem is always to agree upon a new system which is acceptable to everybody.