Today can be purchased by anybody in thousands of stores as well as on the Internet. That hasn’t always been the case, however. In ancient times, the high priests or wise men guarded the sacred records of time.
All calendars, even the modern ones that hang on our walls, are based on astronomy. In the earliest times, the passage of time was measured according to the moon. The time between full moons was the basis of the calculation of passing time, months, and seasons.
There are man-made lunar calendars that have been discovered by scientists that have date back to 32,000 years ago. There are holes in rocks, notches in reindeer bones, and tusks of mammoths that denote the days between moon phases that date back to the ice age. There are also astronomical records that are inscribed on oracle bones that date back to the Shang dynasty of the fourteenth century B.C. that show a Chinese calendar that includes intercalation of lunar months.
Because there was a need to plan for planting and harvesting crops, records needed to be kept and observatories needed to be built to precisely measure these cycles or time and seasons.
There are three basic types of astronomical calendars that have been developed and used over the centuries:
1. The lunar calendar: It was the first calendar, and it was based entirely upon the moon and moon phases.
2. The lunisolar calendar: This calendar was based upon the lunar phases, but every few years a 13th month was added to bring the calendar back into phase with the tropical year.
3. The solar calendar: This is the one that we use today. It is based upon the sun, but a correction is made once every four years to correct it. A day is added at the end of February and we call that year “leap year.”
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