Why does a day on Earth last 24 hours?

We are used to organizing our daily life around the 24 hours that make up a day. However, to be exact, it must be said that in fact, a day on Earth has a slightly shorter average duration: approximately 23 hours, 56 minutes and 4 seconds. This is the time it takes for our planet to completely rotate on its axis, a phenomenon known as a sidereal day. A small and subtle difference which is the reason why, every four years, we add an extra day to the calendar during the month of February.

But what would you think if we told you that the day does not always have the same length on Earth? that in fact, the length of a day on our planet has varied greatly over time… and continues to vary.

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