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

If you mark the ground or cave where specific shadows or sunbeam hits, those markings move and change through the year very very predictably to the inch. Each year specific points are marked and future validated. They also saw same star constellations and moon paths in same place through year, each year repeating

Oldest lunar calendar https://sservi.nasa.gov/articles/oldest-lunar-calendars/