Why is there a difference between a solar day and a sidereal day?
The reason is that one sidereal day is the time that it takes the Earth to rotate 360 degrees on its axis. But in that time, the Earth has continued to move along in its orbit around the Sun. So in order to get back to the point where the Sun is in about the same position in the sky, the Earth has to spin for another four minutes. That’s a solar, or Sun-referenced day.
