What is the difference between a sidereal and solar day?

A day is the time taken by a celestial body to complete one rotation about its axis. The Earth rotates about its axis, and it takes approximately 24 hours to complete one rotation. There are two types of days based on the reference point used to measure the rotation of the Earth: a solar day and a sidereal day.

A solar day is the time taken by the Earth to complete one rotation about its axis with respect to the Sun. It is the time between two successive noons, i.e., the time taken by the Sun to appear at the same meridian twice. Since the Earth also moves in its orbit around the Sun during this rotation, it has to rotate slightly more than one complete rotation on its axis to bring the same point on the surface to face the Sun again. Therefore, a solar day is approximately 4 minutes longer than a sidereal day.

A sidereal day is the time taken by the Earth to complete one rotation about its axis with respect to a fixed point in space. It is the time between two successive transits of a fixed star over a particular meridian. Since the Earth also moves in its orbit around the Sun during this rotation, it has to rotate slightly less than one complete rotation on its axis to bring the same point on the surface to face the same fixed point in space again. Therefore, a sidereal day is approximately 4 minutes shorter than a solar day.