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

Without modern technology and our busy, regimented lifestyle, you have a lot of time to notice the changing of the day length, the seasons, the night sky, etc. There were detailed calendars well before 45 B.C. That said, they believed that the sun orbited the Earth, but the ancient Greeks had already even calculated the size of the Earth by around 200 B.C.