It is unknown who invented the first calendar, but notched bones used to record moon phases date back to 20,500 BC. Now we use days and weeks and to keep track of time.

About Calendars

A calendar is a system of organizing days for social, religious, commercial, or administrative purposes. This is done by giving names to periods of time, typically days, weeks, months, and years. A date is the designation of a single, specific day within such a system. Periods in a calendar (such as years and months) are usually, though not necessarily, synchronized with the cycle of the sun or the moon. Many civilizations and societies have devised a calendar, usually derived from other calendars on which they model their systems, suited to their particular needs.

Contributions by Joe Kress, Karl Palmen, and Patrick.

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