Calendars and years: astronomy and time in the ancient near east

Dates form the backbone of written history. But where do these dates come from? Many different calendars were used in the ancient world. Some of these calendars were based upon observations or calculations of regular astronomical phenomena, such as the first sighting of the new moon crescent that defined the beginning of the month in many calendars, while others incorporated schematic simplifications of these phenomena, such as the 360-day year used in early Mesopotamian administrative practices in order to simplify accounting procedures. Historians frequently use handbooks and tables for conv