Submitted by Slokkkk t3_11dm4k6 in explainlikeimfive
annomandaris t1_jaapimo wrote
Reply to comment by DarkAlman in Eli5: How did people know how long a year was in olden times? by Slokkkk
Long before calendars, farmers knew the lunar schedule of 13 months of 28 days which is 364 days, and they knew it was off so every few years you had to adjust it. This would have been relatively common knowledge around 10-20K years ago.
Babylonians knew 360 was off when they made their calendar, but they didn't care. 360 was just too perfect for dividing stuff. So they just had a 4-5 day holiday after the harvest that didn't go on a calendar. People got a vacation after all that work, and the rest of the year you could divide days in your head. everyone wins.
AliMcGraw t1_jabc0b8 wrote
Lunar months are actually about 29 1/2 days; most ancient lunar calendars that don't correct for the sun use 12 months and come out with 354 days ... which is why Ramadan moves back 11 days every year (purely lunar calendar).
Most ancient calendars do correct for the sun. :) They stick in bonus days in various ways -- whole bonus month every couple years, bonus week somewhere, etc.
jaa101 t1_jab6ayb wrote
> the lunar schedule of 13 months of 28 days which is 364 days
Except that synodic months actually last 30 days, not 28, and there are nearer 12 of them per year than 13.
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