sidereal day definition
The sidereal day is the time it takes for the Earth to complete one rotation about its axis with respect to the âfixedâ stars. By fixed, we mean that we treat the stars as if they were attached to an imaginary celestial sphere at a very large distance from the Earth.idereal Day. A sidereal day is the time it takes for the Earth to rotate about its axis so that the distant stars appear in the same position in the sky. A solar day is the time it takes for the Earth to rotate about its axis so that the Sun appears in the same position in the sky.