Eli5: How did ancient civilizations in 45 B.C. with their ancient technology know that the earth orbits the sun in 365 days and subsequently create a calender around it which included leap years?

Question

Eli5: How did ancient civilizations in 45 B.C. with their ancient technology know that the earth orbits the sun in 365 days and subsequently create a calender around it which included leap years?

In: 6494

Answer 1

Ancient civilizations didn’t have leap years included.

Ancient calendars like the first Roman calendar didn’t much care about being precise, it only had 304 days in it and the ruler added extra days as holidays whenever they felt like it to make up for rest of the year. Is it summer but calendar is already October? Just add a bunch of holidays to sync back up.

Republic calendar already had leap years, but they didn’t count it the same, the error was too much. We didn’t get current Gregorian calendar until 1582. When the switch happened after centuries of calendar drift, 10 days were lost. Next date from October 4 1582 was October 15, the days between did not happen. Unless you were British, then you kept using Julian calendar until 1752 when you lost 11 days.