With respect to the stars, the Moon takes 27 days 7 hours 43.2 minutes to go around in its orbit; but since the Earth-Moon system has advanced around the Sun in the meantime, the Moon must keep going a while longer to get back to the same phase. On average, this synodic period is 29 days, 12 hours, 44 minutes and 3 seconds long. This is an average figure, since the speed of the Earth-Moon system around the Sun varies slightly over a year, due to the eccentricity of the orbit; the Moon's own orbit also undergoes a number of periodic variations about its mean value because of the gravitational perturbations of the Sun.
In oceanography, a lunar day is the period of time it takes for the Earth to complete one full rotation on its axis with respect to the moon. This is the time from one lunar zenith to the next, about 24 hours 50 minutes. This period is also called the tidal day.
Deep Impact and Other Spacecraft Find Clear Evidence of Water on Moon; Thin Layer of Surface 'Dew' Appears to Form, Then Dissipate Each Day.
Sep 24, 2009; Byline: University of Maryland, College Park COLLEGE PARK, Md., Sept. 24 (AScribe Newswire) -- New data from the Deep Impact...