<P> 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; 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 . </P> <P> The following types of months are mainly of significance in astronomy, most of them (but not the distinction between sidereal and tropical months) first recognized in Babylonian lunar astronomy . </P>

Where do you think the length of a month came from