Why Leap Years Don't Happen Every 4 Years

There's one exception to the rule

By Evann Gastaldo,  Newser Staff

Posted Feb 29, 2012 9:37 AM CST

(Newser) – Why do we have leap years? Basically, to ensure that there's a better chance you'll see snow on Christmas than falling leaves. "If we didn't have leap years, our calendar would be totally scrambled," explains a worker at America's timekeeper, Washington DC's US Naval Observatory. Since the Earth doesn't take exactly 365 days to circle the sun, the extra time it takes each year would get us out of sync with the seasons—which is how you might eventually find yourself raking leaves before opening presents on Christmas morning, USA Today reports. You already knew all that? Well, read on.

Julius Caesar first added leap days to the calendar around 46 BC—but the Julian calendar had them once every four years. Think that's the current rule? Not so. That schedule was just a little bit more than the Earth's extra rotational time required, which meant that by the 1500s, things were about 10 days off. So in 1582, Pope Gregory XIII switched it up: His Gregorian calendar removed leap years that fall on turn-of-the-century years ending in "00" that are not divisible by 400. (Meaning we won't have a leap year in 2100, but we did have one in 2000.) The bad news: If you're on a fixed annual salary, you're working for free today, the Daily Telegraph notes.

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