We know about leap years. Every four years, there’s an extra day added to the end of February. Instead of 28 days in the shortest month of the year (which has its own origin story), there is a 29th, giving us 366 days during a leap year. We just so happen to have that extra 24 hours this year, but have you ever wondered exactly why? Well, it has to do with the sun.
A leap year, other scientific terms include bissextile or intercalary year, is actually a correction. If we’re talking specifics, it takes approximately 365.24 days for the earth to make an entire rotation around the sun, called a tropical year. While that extra 0.24 doesn’t sound like much, if we went on without leap years, it would add up over time, causing seasons to shift respective to when we’re used to them. A couple hundred years without that extra day would make fall start after new year’s eve. A few hundred more and we’re celebrating the ball drop in the heat of summer.
Now, this mismatch of seasons actually occurred, and the ancient Romans noticed it over 2 millennia ago, and came up with the leap year in 46 BCE, calling it the Julian Calendar after Juilius Cesar. It wasn’t until Pope Gregory XIII that the calendar was updated to what it is currently, a Gregorian calendar, with rules determining which leap years don’t contain the extra day.
If other planets adopted leap years to keep their years aligned, it would look even more extreme. Take mars, for instance, the planet that closest resembles earth. It’s year takes 668.59 days, which scientists have determined it would have a leap year in any year divisible by 2 or 5, much more frequently than us.
While it’s purpose is to get us back in alignment with our actual rotation around the sun, for us here on earth, it’s essentially an extra day to enjoy. Plus with 2020 leap day falling on a sunday (in 2016, it was on a Monday), it’s safe to say we’ll enjoy this year’s extra sunrise and sunset more than most.