Happy leap day! Today marks an ongoing, longstanding correction to the calendar we use.
In most years, our calendar contains 365 days. But Earth actually takes 365. 2422 days (let’s call it 365¼ days) to orbit the Sun. As you might imagine, if we let these quarter days add up, we’d quickly be celebrating the 4th of July when it’s snowing.
So, we add a full day every four years … almost. A year that’s 365¼ days long actually is 11 minutes longer than Earth’s actual orbit. That means we need additional corrections from time to time. To refine our calendar even further, all years evenly divisible by 400 (the most recent one was 2000) are not leap years.
By the way, the first leap day added to the month of February occurred in the year 8 A.D.