How long does it take Earth to rotate on its axis?
Depends on how you measure it. The mean solar day, that is the average time it takes for the sun to go from its highest point on a given day to its highest point the next day, is 24 hours. If you measure the time it takes a distant star to do that, (the sidereal day) it’s 86,164.091 seconds (or: 23 hours, 56 minutes, 4.091 seconds). The difference is the apparent motion of the sun, which is really caused by the earth moving. Take those (slightly less than) 4 minutes a day each day for a year, and it adds up to one extra day.
