Lunar calendar

[4][5] Scholars have argued that ancient hunters conducted regular astronomical observations of the Moon back in the Upper Palaeolithic.

Thus, to minimise uncertainty, there have been attempts to create fixed arithmetical rules to determine the start of each calendar month.

The algorithm was introduced by Muslim astronomers in the 8th century to predict the approximate date of the first crescent moon, which is used to determine the first day of each month in the Islamic lunar calendar.

Their months are based on observations of the lunar cycle, with periodic intercalation being used to restore them into general agreement with the solar year.

An example of this is the lunisolar calendar of the Banks Islands, which includes three months in which the edible palolo worms mass on the beaches.

These events occur at the last quarter of the lunar month, as the reproductive cycle of the palolos is synchronized with the moon.