In space exploration, a lunar day is the period of time it takes for the Moon to complete one full rotation on its axis. Equivalently, it is the time it takes the Moon to make one complete orbit around the Earth, due to tidal locking. It is marked from a New Moon to the next New Moon.
By Earth's time standards, a lunar day is officially 29 days, 12 hours, 44 minutes and 3 seconds long.
In space exploration, a lunarday is the period of time it takes for the Moon to complete one full rotation on its axis with respect to the Sun.
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 lunar calendars, a lunarday or tithi is defined as 1/30 of a lunar month, or the time it takes for the longitudinalangle between the moon and the sun to increase by 12°.
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