"A month is a unit of time, used with calendars, which is approximately as long as a natural period related to the motion of the Moon; ...
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month and Moon are cognates. The traditional concept arose with the cycle of Moon phases; such months (lunations) are synodic months and last approximately 29.53 days. From excavated tally sticks, researchers have deduced that people counted days in relation to the Moon´s phases as early as the Paleolithic age. Synodic months, based on the Moon´s orbital period with respect to the Earth-Sun line, are still the basis of many calendars today, and are used to divide the year." - (en.wikipedia.org 23.09.2019)