Topic summary
Tropical month
Extracted from the Wikipedia article Lunar month.
Tropical month
Just as the tropical year is based on the amount of time between perceived rotations of the sun around the earth (based on the Greek word τροπή meaning "turn"), the tropical month is the average time between corresponding equinoxes. It is also the average time between successive moments when the moon crosses from the southern celestial hemisphere to the northern (or vice versa), or successive crossing of a given right ascension or ecliptic longitude. The moon rises at the North Pole once every tropical month, and likewise at the South Pole.