While showing nearly the same face to , Moon spins for its day and night. As of now, average Moon’s day is 29.530587891 Earth days.
Here, the period between two consecutive Full Moon’s transits (or New Moon’s transits) of the Earth’s heliocentric ( revolving-about-Sun ) longitutudinal plane determines lunar day.
In brief, it is synodic (defined with respect [the Sun]) lunar month, (http://socratic.org/astronomy/our-solar-system/the-sun-1)-Earth line.
Moon spins through 2##pi## radians, with respect to the Sun, during this period.
