Who Discovered the Earth Was Round?

I was on YouTube the other day and the algorithm recommended to me a video about someone trying to understand how people can still think that the Earth is flat. Flat Earthers is a thing I just can understand myself. It just makes no sense. But this led to the question of the day:

Who Discovered the Earth Was Round?

Yes, at one point in time, all of humanity was composed of Flat Earthers. But it didn’t last as long as you may think. In fact, the idea that the Earth was round has been around since the time of the ancient Greeks.

It was around 500 B.C. that Pythagoras—Ionian Greek philosopher and the eponymous founder of Pythagoreanism—introduced the idea of a spherical Earth. At that time, it was just that, an idea. He didn’t have any scientific proof to back it up. How did he arrive at that conclusion then? He looked at the Moon and deduced that Earth might also be round.

Greek philosopher and polymath Aristotle, around 350 B.C., added more value to the theory by observing lunar eclipses—more precisely, how the shadow of the Earth is cast on the Moon. He also noted that, if the Earth was flat, we would see the same sky as we move around.

Aristotle. Line engraving by Beyssent after Mlle C. Reydelle.

Who calculated the circumference of the Earth?

Another Greek polymath, Eratosthenes of Cyrene, went even further. Around 240 B.C., he became the first person known to calculate the circumference of the Earth. Even if the tools of that time did not allow as much precision as those of today do, his result was quite good.

The story goes like this, Eratosthenes had heard that in a city south of Alexandria named Syene (now called Aswan, in Egypt), no vertical shadows were cast at noon on the summer solstice (June 21st). This observation led him to check in Alexandria to see if it was the same. It was not. If the Earth was flat, why did the sun’s rays not come in at the same angle at the same time of day? Being familiar with the idea of a spherical Earth, he knew well why.

Eratosthenes started to measure the difference in shadow length in the two cities. The result was 7°. He then paid a man to go from Alexandria and Syene in order to measure the distance between the two—5,000 stadia apart (~800 km). He then did some simple maths and obtained a result: the circumference of our planet is 40,000 kilometers.

It’s quite impressive, especially now that we know for sure that the circumference of the earth is 40,075 km! Truth is, Eratosthenes may not be as accurate as it appears, because the length of a stadia changed depending on the country of origin (not unlike the metric system for a time), but it makes for a better story to think his result was this close to the reality.

Who was the first person to sail around the world?

Knowing the Earth was round is one thing, sailing around the world is another. Ask Ferdinand Magellan! It wanted to. He planned for it. He started from Spain but didn’t go beyond the Philippines. He was killed before the end of the trip, contrary to his slave, Enrique of Malacca, possibly.

It’s not sure he made it home, unlike Juan Sebastian Elcano, captain of the Victoria, the only vessel from Magellan’s expedition to return to Spain after their trip around the globe. Therefore, Elcano deserved recognition for having officially completed the first circumnavigation of the Earth.

You can read more about Magellan’s travel in this National Geographic article. And if you’re interested in the creation of the GPS, I wrote an article about it!

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