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

45 BC is not really that ancient – the last year of Julius Caesar’s life. The period known as classic antiquity. We are closer in time to Julius Caesar (100 – 44 BCE) than Caesar was to the first Egyptian dynasties (~3000 BCE).

Keep in mind that ancient humans were just as intelligent as modern humans – they developed the foundations of math, writing systems, structural engineering, understood agriculture, basic metallurgy, pottery/ceramics, etc. all of which they bootstrap without the benefit of widespread, efficient knowledge transfer (literacy, common education, etc.).

Since many things of very high importance to ancient people were dependent on seasons they learned over thousands of years to observe the sun, moon, planets and stars, the length of days, etc. and developed developed instruments to track these important cycles. There is evidence of early calendars going back to the neolithic (10,000 – 4500 BCE) – numerous monoliths, stones or structures that were used to track the solar year and/or lunar month. The Sumerians (~ 2000 BCE) had a solar year of 365 days with 12 months. Leap years were accounted for by periodically inserting days or months.