Earth spins around completely once every twenty-three hours and fifty-six minutes. This, of course, is not exactly twenty-four hours; but it is so close that we have created clocks and calendars to reflect the nice round number of twenty-four hours per day, and compensate in other ways for the difference.

Since Earth is a mostly solid object, every part of Earth takes the same amount of time to complete one rotation. That means, for example, that a person standing on Earth’s equator is actually moving in that rotational motion at some 1,040 miles (1,670 kilometers) per hour—nearly twice as fast as a commercial jet liner! This speed goes down as one moves toward the north and south poles, however; at the poles, the rotation speed would be zero.