What’s Another (Leap) Year?

By TADHG CURTIN

2024 is a leap year. As we all know, a leap year occurs every four years leading to an extra day on the calendar. Instead of the normal 28 days, February will have 29. You may know or even be someone who celebrates their birthday on this unique day. But as much as I knew about leap years, I realised how little I knew after. What is the exact science and why do we have leap years?

A calendar year is typically 365 days long. These so-called “common years” loosely define the number of days it takes the Earth to complete one orbit around the Sun. But 365 is actually a rounded number. It takes Earth 365.242190 days to orbit the Sun, or 365 days 5 hours 48 minutes and 56 seconds. This “sidereal” year is slightly longer than the calendar year, and that extra 5 hours 48 minutes and 56 seconds needs to be accounted for somehow. If we didn’t account for this extra time, the seasons would begin to drift. This would be annoying if not devastating, because over a period of about 700 years our summers, which we’ve come to expect in June in the northern hemisphere, would begin to occur in December!

A leap Year or ‘sidereal’ year is 366 days in length as opposed to the standard 365 days, Earth time.

By adding an extra day every four years, our calendar years stay adjusted to the sidereal year, but that’s not quite right either. Some simple math will show that over four years the difference between the calendar years and the sidereal year is not exactly 24 hours. Instead, it’s 23.262222 hours. Rounding strikes again! By adding a leap day every four years, we actually make the calendar longer by over 44 minutes. Over time, these extra 44+ minutes would also cause the seasons to drift in our calendar.

For this reason, not every four years is a leap year. The rule is that if the year is divisible by 100 and not divisible by 400, leap year is skipped. The year 2000 was a leap year, for example, but the years 1700, 1800, and 1900 were not. The next time a leap year will be skipped is the year 2100.

For the romantics out there, February 29th is also a day where women can propose marriage to a man. I know we are all hip and modern so that shouldn’t matter to a lot of you but, yes, rather than men, women get to bend the knee on this day. Reffered to as ‘Bachelor’s Day’, the Irish tradition is supposed to originate from a deal that Saint Bridget struck with Saint Patrick. In the 5th century, Bridget is said to have gone to Patrick to complain that women had to wait too long to marry because men were slow to propose, asking that women be given the opportunity. Patrick is said to have offered that women be allowed to propose on one day every seven years, but Bridget convinced him to make it one day every four years. Hence, Bachelor’s Day.

The Irish tradition of women proposing marriage to men on February 29th is said to have begun with St. Brigid and St. Patrick.

So, happy Leap Year to you all! To deliberately misquote a John Lennon song, “So this is Leap Year, and what have you done?” Well, give us a chance. We’re only getting started...