Sidereal Time

Astronomers make use of the sidereal day, which is the time required for the Earth to make one complete rotation (360°) with respect to the stars. The "day" that is used in everyday life is the solar day, which is (approximately) the time from when the Sun is highest in the sky to when it is again highest in the sky. Because the Earth moves around the Sun as it rotates, in one solar day the Earth must rotate through about 361°. A solar day is about 4 minutes longer than a sidereal day.