Every four years, the universe plays a little game of catch up by adding an extra 24 hours to the 365-day calendar.

It takes the earth roughly a year to rotate around the sun. But “roughly” doesn’t cut it for scientists, and the extra few hours of rotating didn’t go unnoticed. Rather than making each year 365.25 days, the calendar-making geniuses compiled those extra quarter days to give us one whole bonus day. Why they chose the worst month of the year for the bonus is still a mystery.

It’s just a quarter of a day – what’s the big deal? Without leap days, in three decades the calendar would be off by a week, eventually the seasons would flip and Christmas would fall in the summer (making Santa one sweaty man in that velour suit).

Leap years explained by people who know: