Why is a day on earth 24 hours long?

The day lasts 24 hours just because people wanted to share it like this. There is nothing in nature about hours, minutes and seconds. This division of time was made by man according to his wish.
But there is something in nature that happens in one day. Each time the Earth rotates once about its axis, a certain time passes, which we call a day. Using stars, scientists can accurately measure time. In observatories, a day begins when a star crosses the meridian and lasts until it crosses it again.

Since man divided the day into hours, minutes and seconds, we can say exactly how long a day lasts: 23 hours, 56 minutes, and 4.09 seconds. This is called a sidereal day. But since it would be difficult to use sidereal day in practical life, we take the day to last 24 hours, so we add a leap year to correct the difference.

Image by Gerd Altmann from Pixabay

In the old days, people thought that the day lasted from sunrise to sunset. The duration of the night was not counted. The Greeks reckoned that the day lasted from sunset to sunset and the Romans from midnight to midnight.
While the clocks had not yet been discovered, it was calculated that day and night lasted 12 hours each. Such a division was not practical, as the length of day and night varied between seasons. Today in most countries, the law stipulates that the day lasts 24 hours, from midnight to midnight, according to Roman times.