Today’s unusual date of 29th February 2016 occurs only once every four years, but who knows why this is?
Why do we have leap years?
Because of the disparity between the solar system and the Gregorian calendar, a little catching up and adjustment is required. For the earth to orbit the sun, it takes exactly 365.2422 days, but the Gregorian calendar uses only 365 so it becomes necessary to add 24 hours every four years in order to keep our clocks and calendars in sync with the earth and its seasons.
Why does this occur in February and not another month?
We need to go back to the time of the Roman times to find the answer to this. Julius Caesar added extra days to ‘his’ month July and at the time August only had 29 days. When Caesar Augustus became emperor after Julius, he adjusted the months taking the days from February and adding them to ‘his month’ August to make it the same as July. February lost out and the days were adjusted for egotistical reasons alone.
Before Julius Caesar came to power, people had observed a 355 day calendar and an extra month of 22 days was added every two years. This was not an ideal solution however with feast days moving between different seasons. The astronomer Sosigenes was ordered by Caesar to simplify things. Sosigenes decided the best way to create the extra hours was to settle on the 365 day year with an extra day every four years. Thus the 29th February was created.
Things do not stop here however, as there are also other rules. Every fourth year is usually a leap year. The ruling states that there is a leap year when that year is divisible by four, except where it divisible by 100 and not by 400. So the year 2000 was a leap year exactly like the year 1600, but 1700, 1800 and 1900 were not. The rule for centuries was added to make up for the fact that an extra day every four years would be an over correction resulting in too many days being added.
Essentially a year is 365 days, but it is not exactly so. In 1582 when Pope Gregory XIII and his astronomers introduced the Gregorian calendar, their aim was to lose 3 leap days every 400 years. This has proven successful in terms of the mathematics of the whole science of calendars and seasons for centuries and not something which will change any time soon.
As well as the science and astronomy surrounding 29th February, there are also other interesting facts associated with this date. It is said that the tradition of women proposing to their menfolk is something which is allowed on this date, and is actively encouraged. Where this idea came from is debateable however, with one source attributing St Bridget in the 5th Century. She apparently complained that women had to wait too long for proposals from their suitors to St Patrick who allegedly offered women the single day in a leap year to pose the proposal, being the last day of the shortest month, or in other words, not a large window of opportunity at all!
A more popular theory dates back to when the leap year day was not recognised by English law and under this theory, the tradition of a woman proposing on a day which did not officially exist meant it was a break from convention and possibly more acceptable.
If you are celebrating your birthday today, firstly congratulations Leapers! The chances of this happening are said to be one in 1,461. This is calculated by working out the number of days in four years (1,460) and adding one for the leap year. Anyone who is lucky enough (or may consider it actually unlucky) to be born on the 29th February, will usually celebrate their birthday either on 28th February or on 1st March, depending on the time of day they were born. Rarely, people do not celebrate the in-between-leap-birthdays and adhere to the strict regime of only one birthday every four years. There are about 4.1 million people in the world who were born on 29th February.
There are other calendars which use leap years to adjust their days and years. The modern Iranian calendar is a solar calendar with 8 leap days added to a 33 year cycle. The Indian National Calendar and the Revised Bangla Calendar of Bangladesh organise their leap years so that the leap day is always near to 29th February in the Gregorian calendar.
In 1504 the explorer used the lunar eclipse to his advantage while he was on a trip to the West Indies. He had been stranded for several months in Jamaica and was running short on supplies after relations with the indigenous population broke down. He knew a lunar eclipse was due, and having consulted his almanac he gathered the native chiefs on 29 February. He told them God would punish them by painting the Moon red. While the eclipse occurred, he said that God would only stop the punishment if they starting co-operating again. The worried chiefs agreed and the Moon began emerging and returning to its normal hue.
Leap seconds serve the purpose of keeping the earth’s rotation in line with our calendars and clocks. They are added to bring the line of the earth’s rotation in sync with atomic time. The earth’s rotation is gradually slowing down by around two thousands of a second per day, so in order to keep this rotation in line, the leap seconds have to be added to prevent time ‘slipping’ and the changes from day into night at the correct times. When this extra second is added, some technologies seem to falter. 4 years ago in June 2012 problems were reported by various operating systems and programmes which did not understand the addition.
It is very unlikely however that today’s date has escaped many people’s notice, as it is something we like to celebrate, especially as it only happens every four years.