QUOTE:
Originally Posted by Toadette29
It really takes 23 hours 56 minutes for the Earth to spin 360 degrees. Thus, leap years exist.
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Sorry, that's not actually true. The reason that we have leap years is because it takes 365.24 days for the earth to orbit the sun once. The extra 0.24 days causes the addition of the leap year every 4 years (less 3 every 400 years), such that our calendar does not get out of step.
The extra 4 minutes in what is defined as a day is a side effect of the fact that earth is orbiting the sun. During that day, the earth moves about 1 degree around the sun. Because of this earth needs to rotate by around 361 degrees, such as to have the sun directly overhead in the same place as it was the day before. (This is how the day was originally defined, as it would appear from earth that earth has rotated by 360 degrees, because the orbit is not detectable).