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Why does Leap Day exist?

Happy Leap Day!

Once every four years, we get an extra day on the calendar, so 2024 will have 366 days instead of the traditional 365 days. But why?


The Earth’s orbit around the sun (one year) isn’t exactly 365 days – it’s exactly 365.242190 days. So every year, there’s a leftover 5 hours, 48 minutes and 56 seconds that goes unused. That extra time eventually adds up, and every four years it roughly adds up to an extra 24 hours.

So on that fourth year, the extra day is needed to account for the extra time!

If we didn’t account for the extra time, the seasons would slowly slide century after century…. so much so that a several hundred years from now, summer would start in December, not June! Wouldn’t that be weird!? Weirder than simply adding an extra day to the calendar every four years.

-Steve

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