Four. “Generally speaking, when a body rotates round a circle, it always does one revolution more than one can count. It is precisely this that explains why the earth, revolving round the sun, succeeds in rotating on its axis not in 365 1/4 days, but in 366 1/4 days, if one counts its revolutions in respect to the stars and not the sun. You will understand now why sidereal days are shorter than solar days.”

From Perelman’s Figures for Fun, 1957.