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 lunar calendars, a lunar day
is defined as one 30th of a lunar month
, or the time it takes for the longitudinal angle
between the moon
and the sun
to increase by 12°
. By this definition, lunar days vary in duration (see tithi