Why do we have a leap year

Why are there leap days?

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The year has 365 days. That is how long it takes the earth to orbit the sun. Then a new solar year begins. This is what the Greek astronomer Hipparchus said almost 200 BC. Calculated.

According to his calculation, however, it was not exactly 365 days, but 5 hours, 55 minutes and 12 seconds more.

That is almost a quarter of a day! But there cannot be a quarter of a day. What to do?

The Roman general Julius Caesar had the solution: every four years there is an additional day in the year, a leap day. With the Julian calendar he introduced, the time calculation should be correct again. They thought.

But Hipparchus had miscalculated: by 11 minutes and 14 seconds. Accordingly, there was one leap year too many every 128 years. And that had an impact on the seasons. The beginning of spring shifted more and more into winter.

When the spring of 1582 began ten days early, Pope Gregory corrected the calendar by the missing 11 minutes and 14 seconds. He introduced the Gregorian calendar, which we still use today. A solar year therefore lasts 365 days, 5 hours, 48 ​​minutes and 46 seconds. That is 365.25 days.

The leap year continues - but no longer just every four years. The calculation has become a little more complicated:

All leap years divisible by 100 are canceled, for example in 1900 and then again in 2100. But because that would not be entirely correct, there is another exception to this rule: All leap years that are divisible by 400 remain leap years , so 1600, 2000 and then again 2400.

So the year 2000 was a leap year, because 2000 is divisible by 100 and 400. On the other hand, 2100 will not be a leap year because 2100 is not divisible by 400. So for everyone whose birthday is on February 29th, it's best to get a calculator right away so that they don't miss their next birthday. :-)