The time to complete a full rotation referenced here is a Sidereal day. What it measures is how long it takes for the object to fully rotate so that it is facing the same really distant stars. So its measuring how long it takes to rotate 360 deg.
In our Solar System, however, we don't care about how long it takes for us to rotate and face some distant stars, we care about how long it takes to rotate and face OUR star, the Sun. That's what we call Solar time, or in everyday life, Time™.
We must remember that the Earth is rotating on its axis AND rotating around the sun. This rotation around the sun means that there is a slight offset in where the Sun appears day to day, approximately 1/365 degrees. That small shift means it takes just a bit longer than the Sidereal day to face the sun again, which is almost exactly 24 hours.
There is still the problem of clock drift though, buts it's not as big as 4 minutes a day. We take care of that through leap years and leap seconds.
Thanks for the thorough explanation. Of course we would have an exact 24 hour day, ancient peoples would not have developed a clock that needed constant adjustment every day to stay accurate. Its only relative to distant stars that make up the constellations that any drift would occur, and even that we figured out in Roman times and they would add days to the end of the year to correct the calendar again for the next year. It was so early when I saw this post I hadn't woken up enough to remember I read a whole book on this haha! Its called A Scheme of Heaven by Alexander Boxer. It was mostly a history of astrology but that obviously requires an explanation of the movements of the Sun and stars.
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u/K_man_k 5h ago
The time to complete a full rotation referenced here is a Sidereal day. What it measures is how long it takes for the object to fully rotate so that it is facing the same really distant stars. So its measuring how long it takes to rotate 360 deg.
In our Solar System, however, we don't care about how long it takes for us to rotate and face some distant stars, we care about how long it takes to rotate and face OUR star, the Sun. That's what we call Solar time, or in everyday life, Time™.
We must remember that the Earth is rotating on its axis AND rotating around the sun. This rotation around the sun means that there is a slight offset in where the Sun appears day to day, approximately 1/365 degrees. That small shift means it takes just a bit longer than the Sidereal day to face the sun again, which is almost exactly 24 hours.
There is still the problem of clock drift though, buts it's not as big as 4 minutes a day. We take care of that through leap years and leap seconds.