Why is a solar day longer than a sidereal day?
The length of a day is usually defined as the amount of time it takes from when a star or the Sun crosses the celestial meridian, until that same object crosses the meridian again. As you know, the Earth orbits around the sun over a period of about 365.25 days. So, with each passing day, the angle between the Sun, the Earth and the stars, changes by about a degree. And where as the angle that the Earth must rotate from when a star crosses the meridian, until it does so again, is almost exactly 360 degrees; the Earth must spin nearly a full degree more before the Sun again crosses the meridian. Thus the Solar Day takes about 4 minutes more to complete, than does a Siderial day.
