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24 hours (approximately). The "solar day" is exactly 24 hours, but it actually takes about 23 hours and 56 minutes for the Earth to rotate once.

The extra four minutes are needed to allow for the change in position of the Sun in the sky due to the Earth orbiting the Sun.

Answer:

While the basis for the hour is the length of the "solar day" split into 24 parts (so you'd think the day should be 24 hours long - exactly), this is only an average value, not an absolute value. At the equinoxes and solstices the day can be up to 19 seconds longer or shorter. Added to this is the gradual slowing down of the Earth's rotation due to the tidal friction which stretches the day slightly longer than it was in the past.

Edit: To clarify that Answer, there is something called the "sidereal day" which is the rotation time. But there's also the "solar day" which is exactly 24 hours.

That's what we normally call "a day", on Earth. Strictly speaking it's called the "mean solar day".

The word "mean" is just another way of saying "average".

There are variations in the "apparent solar day", but the "mean solar day"

averages out all the slight differences. This gives us the exact 24 hour day

which is, of course, much more convenient.

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12y ago

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