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
Ancient peoples were as intelligent as we are and had lots of tools. For example, they could count the days of the year, and could measure the height of the sun in the sky using things like the length of the shadow cast by a pole or tower, so they could see it was about 360+ days from when the shadow was longest, until the next time it got that long and they could see that it was always summer when the shadow was shortest and winter when it was longest, so clearly the seasons were linked to how high the sun was in the sky, and to how many days had passed since the previous winter. And this was very useful information as it helped them figure out when to plant, or when to hunt migrating herds or seasonal wild food plants and so on.
So over many years of observation and record keeping they would have figured out that the length of the year was 365 days, but you had to add a day now and then to keep it working.
Most ancient civilizations did not know the earth orbited around the sun. However some ancient thinkers might have suspected it. We don’t know who first came up with the idea, but Copernicus pretty much proved it, so he gets the main credit. As well we don’t know who first suspected the earth was a sphere but it’s possible it was thought of by some ancient thinkers long before the ones we credit. The clues were there, for example ships or mountains seeming to drop below the horizon, the farther away they were.
And all this would have happened long before 45 BC – maybe thousands of years earlier. Stonehenge might have been started around 3000 BC and it contains a fair amount of advanced astronomical features, that would have been based on knowledge people might have been developing from even much earlier.
Edit: Okay people, Galileo, Newton and probably others provided proof of Copernicus’s model.
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