When you ask most people how many days are in a year, most would probably reply 365, and they aren’t really wrong – you can see it on any 3 out of 4 calendars after all. However, in reality, the solar year is approximately 365.2422 days long, which is conveniently about a quarter of a day, meaning that by adding February 29th every four years, we are more or less back on track. The tradition is actually very ancient, and in some cultures, this is also the day when women can propose to their sweethearts – it seems that, historically, people really don’t like wasting time!
The ancient Egyptians used to measure the year in 12 months with exactly 30 days, leaving 5 extra days at the end of the year which were given over to festivals, which sounds like a rather fun system. The Chinese Lunar calendar and the Hebrew Calendar take a different approach, adding a leap month every few years to balance the loss with important factors such as the cycle of the moon and the religious rules dictating that certain holidays must not fall on certain weekdays.
Even Roman Emperors had an issue with the difference between calendars and the astronomical year, tweaking the year to make up for lost time. After Julius Caesar introduced a 445 day “Year of Confusion” to fix the difference from years of date shift, the Julian Calendar then became much like ours, with 365 days and a leap day every four … which didn’t work! The new system caused the calendar to create an extra day every 128 years, and some dates had moved by over a week. The Gregorian Calendar introduced many of the months we are familiar with in 1582 and lopped 10 extra days off the year to get back on track.
Our system now, where we add a day in February ever 4 years, causes the year to “leap” over a day, meaning that instead of the days of the week sliding by one position, they “leap” by two. We also skip leap years divisible by 100, with the exception of years divisible by 400, like 1600 and 2000, so the last “lost” leap day was in 1900. This system keeps the days from getting away from us, and shouldn’t cause any problems for a few thousand years.
So leap year babies, or “leaplings” – Happy Birthday! You may only get a “real” birthday every four years, but just remember, thousands of years of thought has gone into it.