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
Earth and return to the same
phase. A lunar month is the period between two
new moons and lasts about 29.5 days.
Relative to the
fixed stars on the
celestial sphere, the Moon takes 27 Earth
days, 7 hours, 43 minutes, and 12 seconds to complete
 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
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.