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.