2020 is a leap year, and Saturday, February 29th is leap day – but why exactly do we have leap years, and why do they only occur every four years? We’ve got you covered. Here’s all you need to know about leap years:
If you were to ask anyone how many days are in a year, they’d almost certainly respond with “365.” The Earth needs a bit more time to make one complete orbit around the sun, however. One complete orbit takes 365.256 days, or roughly 365 days and six hours.
Losing a few hours each year isn’t a huge deal – but over long stretches of time, those extra days would add up, and suddenly the calendar would unravel, and seasons around the world would no longer correspond to the months we’ve become accustomed to.
In 45 BC, inspired by the Egyptians’ solar calendar, Julius Caesar introduced his 365-day Julian Calendar, which included one leap year every four years, with a leap day added in February.
Caesar’s math was slightly off, however, and his system still could not account for a loss of 11 minutes each year. More than a thousand years later, this discrepancy was fixed by Pope Gregory XIII, who introduced what we now call the Gregorian calendar. Under the new system, a leap year was still observed every four years – unless it was a “century” year (1500, 1600, 1700) that was not divisible by 400 (such as 2100).
The Gregorian calendar also had to make up for the time lost during the period the Julian calendar was used, so the days between October 4th and October 15th were skipped. When you went to sleep on October 4th, you woke up on October 15th.
If you’re more of a visual learner, FTW alum Greg Presto explained leap years in this very helpful video.
