On a prograde planet lik the Yird, the sidereal day is shorter nor the solar day. At time 1, the Sun an a certain distant starn are baith owerhead. At time 2, the planet haes rotatit 360° an the distant starn is owerheid again (1→2 = ane sidereal day). But it is nae till a little later, at time 3, that the Sun is owerheid again (1→3 = ane solar day). Mair simply, 1-2 is a complete rotation o the Yird, but acause the revolution aroond the Sun affects the angle at which the Sun is seen frae the Yird, 1-3 is hou lang it taks noon tae return.
Solar time is a reckonin o the passage o time based on the Sun's poseetion in the sky. The fundamental unit o solar time is the day. Twa types o solar time are apparent solar time (sundial time) an mean solar time (clock time).