How and when was it first discovered that the Earth is not flat?
(ORDO NEWS) — Long before Magellan circumnavigated the Earth, and before the Greek philosopher Pythagoras confirmed that the Earth was round (500 BC), and before Aristotle declared the Earth to be a sphere, based on his constellation observations (350 BC), we should go back in time a little earlier, to 200 BC. and remember the Greek mathematician and astronomer Eratosthenes of Cyrene, who was the first to measure the circumference and diameter of the Earth.
Interestingly, he did not leave the city of Alexandria. He had no other tools than mathematics. What is surprising is that the data obtained is incredibly accurate for that time, given the available technology.
While in the Library of Alexandria, he found an observation report of Syene, a city located about 800 km south of Alexandria (although he did not know how far it was at the time), which stated that on the day of the summer solstice ( June 21) in Siena, located about 800 km south of Alexandria, at noon objects did not cast a shadow, and sunlight could be seen at the bottom of the pits.
Thinking about it in Alexandria on the same day and at the same time, he noticed that this very fact had not happened. He could not reproduce what was stated in the library document. Why?
His reflections led him to speculate that the reason is that the Earth is curved and therefore there is a difference in shadows in the two cities.
Thus, if the shadow in Syene were a certain length, and the shadow in Alexandria were the same length, then this would also mean that the Earth was flat. But it wasn’t.
To test this, Eratosthenes conducted a very simple but effective experiment.
By measuring the length of the shadow cast by a vertical stick at the noon solstice (when the shadow was shorter) in Alexandria, he was able to calculate what angle the Sun would make with the vertical direction in Alexandria.
The answer was: one fiftieth of a circle, or 7.2 degrees. At that time in Siena, the angle formed by the Sun with an identical vertical stick was zero degrees.
Given these data, and taking into account the distance between the two cities, he calculated that the radius from one city to the other was approximately equal.
Eratosthenes paid a man to walk from Syene to Alexandria to find out how many kilometers between cities.
The distance from the center of the Earth must have been about 6,000 kilometers (estimated at 6,244 to 7,358 km).
When measuring it, the scientist was slightly wrong by a small percentage of the value accepted today (the accepted radius of the Earth is 6371 km).
In conclusion, he concluded that the circumference of the Earth is 250,000 stadiums, with the average stadium being 160 meters, giving a figure of 40,000 km.
This figure is more than close to the real one, which is 40,075 kilometers. Regardless of the chosen average stadium size, the accuracy remains stunning.
The conclusion of the mathematical experiment is impressive, and thanks to the fact that he became the first geographer on the planet, we had the concepts of latitude and longitude that we still use today.
The only tools the Greek sage used were sticks, eyes, legs, and brains. With the help of these objects, he determined the circumference of the Earth with a small error.
Simply by observing the differences in the angles of the Sun from two different locations, he was able to calculate the circumference of the Earth and at the same time show that it was indeed round and not flat.
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