<P> A lunar day is the period of time for Earth's Moon to complete one rotation on its axis with respect to the Sun . Due to tidal locking, it is also the time the Moon takes to complete one orbit around Earth and return to the same phase . A lunar day is the period between two new moons . </P> <P> Relative to the fixed stars on the celestial sphere, the Moon takes 27 Earth days, 7 hours, 43 minutes, and 12 seconds to complete one orbit; however, since the Earth--Moon system advances around the Sun at the same time, the Moon must travel further to return to the same phase . On average, this synodic period lasts 29 days, 12 hours, 44 minutes, and 3 seconds . This is the mean figure since the speed of the Earth--Moon system around the Sun varies slightly during a year due to the eccentricity of its elliptical orbit, variances in orbital velocity, and a number of other periodic and evolving variations about its observed, relative, mean values, which are influenced by the gravitational perturbations of the Sun and other bodies in the Solar System . </P> <P> As a result, daylight at a given point on the Moon would last approximately two weeks from beginning to end, followed by approximately two weeks of night . </P> <P> The term lunar day may also refer to the period between moonrises or high moon in a particular location on Earth . This period is typically about 50 minutes longer than a 24 - hour Earth day, as the Moon orbits the Earth in the same direction as the Earth's axial rotation . </P>

Why is the length of a lunar day different from the length of a solar day