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|Ivars Peterson (MathTrek)|
|Calendars represent our efforts to create frameworks that allow us to reckon time over extended periods. We normally count the day - the time it takes Earth to rotate once on its axis - as the smallest unit of calendrical time. The measurement of fractions of a day fits, by convention, into the category of timekeeping. Of the 40 or so calendars presently used in the world, the most common ones group days into weeks, months, and years. They follow two astronomical cycles in addition to the day: the year (based on the revolution of Earth around the sun) and the month (based on the revolution of the moon around Earth). The trouble is that the cycles of revolution do not comprise an integral number of days...|
|Levels:||Middle School (6-8), High School (9-12), College|
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