- Acoreus
Acoreus was a wise man consulted by
Julius Caesar , according to the Roman writer Lucan, asking him many questions aboutancient Egypt ’s history and its calendar. Caesar learned that the Egyptians based their year on thesolar year , that is, on the apparent motion of theSun through all of thezodiac al constellations, and that the Egyptians knew that such a year averaged 365 1/4 days.The
Egyptians were the first people to base their calendar on the solar year, though in a form that caused it to wander through all the seasons, based on the annual flooding of theNile . Their calendar year had just 365 days, organized into 12 months of 30 days each with fiveepagomenal day s added to the end of each year. Although they realized that their year wandered, they did not attempt to stop it until238 BC , when the pharaoh Ptolemy III attempted to add an extra day to every fourth year, but these leap days were apparently never implemented. He may have based hisintercalation frequency on theCallipic cycle , which consisted of 76 solar years averaging 365¼ days each, invented about a century earlier by the Greek astronomerCallippus . Although that cycle was never used in any calendar, knowledge of it would have resided in the greatlibrary at Alexandria , established byPtolemy II several decades earlier.Julius Caesar based his calendar on this Egyptian knowledge of the average solar year supplied by Acoreus and Sosigenes.
ee also
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Julian calendar
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