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

You don’t need to know that the Earth orbits the Sun to create a calendar. All you need is the length of the year, and you can get that by observing the sun and stars.

You can tell if your calendar is drifting out of sync with the seasons, again using observations of the stars.