Eratosthenes calculated the circumference of the Earth about 220BC, he was out by <50 miles on the modern accepted value.

He pre-dated Copernicus by a mere 1500 years.

Educated people have known for a long time that the earth is spherical is what I'm getting at, For many hundreds/thousands of years what the educated class knew and what the rest of society knew was often wildly divergent - as you'd expect in a society with no formal education system where only the wealthy or the sons of the wealthy could afford to spend the time educating themselves/tinkering.

Hu? This is completely unrelated.

The overall idea of a spherical earth is a consensus since ancient Greece, and has been considered a fact since then.

Copernicus more or less established that the earth revolves around the sun, and not the other way around.

I use "more or less" here because

1) The idea of the earth revolving around the sun was not _new_, it was already discussed and debated in ancient Greek texts. Part of the renaissance movement is based on the re-study of ancient Greek texts, which was influential to Copernicus and his ideas.

2) There is no universal truth behind what revolves around what. It's just a matter of perspective, and having the earth rotate around the sun did had the advantage of making calendar computations much simpler, since you don't have to deal with intricate planet retro-cessions. That was the reason that led Copernicus to choose this perspective.

Just about the point that it was a consensus since ancient Greece: it certainly wasn't a consensus around the world until somewhat recently

According to Wikipedia: "Many ancient cultures subscribed to a flat Earth cosmography, including Greece until the classical period, the Bronze Age and Iron Age civilizations of the Near East until the Hellenistic period, India until the Gupta period (early centuries AD), and China until the 17th century.

The idea of a spherical Earth appeared in Greek philosophy with Pythagoras (6th century BC), although most pre-Socratics (6th–5th century BC) retained the flat Earth model."

Interestingly, it seems nobody but the Greeks independently discovered the spherical earth model

But it was certainly a consensus in educated Western Europe, or Columbus wouldn't have been heading west to get to the East Indies (his innovation was to be obstinately wrong about the diameter of the Earth, which would have doomed the voyage but for the fortunate collision with the Carribean)

https://www.youtube.com/watch?v=Df-uemc-e3w

I wonder what he was really thinking:

a) "I believe the distance is smaller and that we'll be able to get there no problem (as much as a trip like that could be ""no problem"")"

b) "distance is bigger but there might be something in between, etc, and I like adventures"

c) "distance is (or might be) bigger and this will be a very boring trip but we'll eventually get there but might have to wing it.

We don't have to wonder, because he wrote it down.

Ptolemy estimated that the continents of Europe and Asia collectively spanned 180 lines of longitude, leaving 180 to travel by sea. Most contemporary scholars believed this too. In actuality, the continents span about 130 from China to Spain, leaving 230 that would need to be travelled by sea. The best sources available to Columbus were wrong, and the other available sources typically erred on the ocean being too small. Few, if any, people thought Europe and Asia spanned less lines of longitude than estimated by Ptolemy.

Additionally, he read that each line of longitude spanned 56 2/3 miles at the equator. Unfortunately, his source was quoting Arabic miles, but Columbus was only familiar with Roman miles, which are shorter.

He didn't believe that he discovered something the scholars of the day didn't. The fragmentation of the Mongol Empire meant that overland trade was growing more expensive, meanwhile nautical technology and seamanship was rapidly advancing. It would have been impossible to have made Columbus' planned (as he understood it) sea voyage in, say 1300. But now, the overland route wasn't well run, and the caravels used by Columbus were much better suited to ocean travel.

If Columbus hadn't done it, the economic necessity of the rising price of goods and dropping costs of sea travel would have resulted in someone else doing the same thing. Some people say he was a unique visionary, other people say he was dumb and lucky. Neither were true. He did his research and came to the natural (if wrong) conclusion. (he was lucky though)

https://en.wikipedia.org/wiki/Christopher_Columbus#Geographi...

> The fragmentation of the Mongol Empire meant that overland trade was growing more expensive, meanwhile nautical technology and seamanship was rapidly advancing.

The fall of Constantinople and the the Ottoman Empire Also made trade routes more expensive

There were also efforts to circumnavigate Africa for this reason

Thanks for this comment, I didn't know about those details.

And yes if it wasn't him it would have been someone else.

d) I will open up a new commercial route starting directly from western Europe to reach India without the hassle of crossing the whole Europe on ground.

Yes but you have to get there first.

Going west from Europe to India doesn't make sense today, it seems the Cape of "Good Hope" was reached (but not crossed) before Columbus's voyage.

It's still a very popular route for sailing. You essentially ride the tropical conveyors from the Azores until the Indian Ocean. The Americas are a minor inconvenience, solved by the Panama Canal.

It's getting back which is the issue - your have the disastrously weathered cape of good hope, or the pirate-infested Aden. It's quite ironic that if you want to sail around the world, it's the ancient routes that are the worst parts.

If Columbus had discovered the Americans were an archipelago, or if the gulf of mexico had properly separated north and south, the discovery would have been a very popular trade route - even today.

What if rising sea level puts Panama under water?

A bit out of my wheelhouse, but I tend to believe the drawbacks would outweigh the benefits.

My bad, I was just commenting on it because it seems like a very primitive model of physics developed by islanders. It makes me wonder why people are still debating about these things even if they are facts. Maybe it's because most people can hardly math. You can blame half the bullshit on conspiracy mongers.

Damn though, engineering mishaps are bad :/

I think you may be confusing heliocentrism with "round" earth? The ancient Greeks and (nearly) everyone since believed in a round earth. They also believed in geocentrism. And Copernicus had the broadly right idea, but convinced very few people since his idea was wrong. Kepler is the one who really convinced people that heliocentrism, because his model was quite accurate in its predictions and was thus able to overcome Aristotle's arguments for geocentrism.

Kepler's boss, Tycho Brahe, had a charmingly incorrect model that had the sun and moon orbiting the Earth while the other planets orbited the sun. It's like heliocentrism with the frame of reference locked on the Earth.

Models are supposed to have a purpose. They give you a way to better understand, visualise, stimulate etc. I don't think an isolated tribe would really have any need to create models in this way. And the curiousities of creation can be explained using myths and legends. Those kind of stories are more compelling and apparently useful than a mundane physical understanding or reality. Particularly when those people already have an intimate understanding of the physical world ingrained.