Already 2000 years ago there was the thesis that the earth is a sphere. Not only Aristotle observed phenomena that supported this idea.
Kassel – It has been known for centuries that the earth is spherical and not flat. As early as the fourth century BC, the well-known philosopher Aristotle observed a lunar eclipse in which the earth cast a circular shadow on the moon. Based on this observation, he made the claim that the earth must be a sphere, as Planet Knowledge explains. Eratosthenes, a Greek mathematician, came up with the same thesis as Aristotle, but for a different reason.
Eratosthenes heard that in Syene, modern-day Aswan in southern Egypt, the sun was reflected in the water of a well. However, this only happens on one day a year, on the day of the summer solstice on June 21st. This observation meant for the scientist that the sun must be directly above the well. In order to check whether the sun is also vertically above the ground in Alexandria, in northern Egypt, on the same day and time, Eratosthenes merely stuck a stick into the ground – and it actually cast a shadow. The mathematician concluded that the earth’s surface must be curved and the earth a sphere.
Greek mathematician knew the earth was round – and calculated its circumference
In addition, with the help of his observation, Eratosthenes was now able to calculate the circumference of the earth. Based on the length of the shadow and the angle of incidence of the sun on earth (seven degrees) in Alexandria, he calculated a circumference of almost 40,000 kilometers. Since the actual circumference of the earth is actually 40,077 kilometers according to the current state of knowledge, the mathematician was not far away.
Eratosthenes arrived at this number by first measuring the distance between the two cities of Syene and Alexandria. “One is not quite sure how Eratosthenes actually did it. The most obvious method at that time was a pedometer,” explains Benjamin Männel from the German Research Center for Geosciences in Potsdam on Deutschlandfunk. Pedometers are people who walk particularly evenly. The result: 5000 stadiums. This result corresponds to about 800 kilometers.
The earth is round: A Greek mathematician calculated the circumference of the earth using a stick
Even then circles were divided into 360 units. According to the findings, Syene and Alexandria are seven degrees apart on the “circle of the earth”, which is one-fiftieth of the entire circumference. Since the distance between the two cities was 5,000 stadia, the mathematician only had to multiply this distance by 50 and thus came up with a circumference of 250,000 stadia.
Various values for stadiums were in use at the time. Since the original records of Eratosthenes no longer exist, it is not known exactly what value he calculated with. In the best case, the mathematician came up with a circumference of almost 40,000 kilometers, which corresponds to a deviation of around one percent from the value measured today, as reported by Deutschlandfunk. In the worst case, Eratosthenes calculated the earth’s circumference a little too high – with a deviation of almost 16 percent. Either way, Benjamin Männel appreciated the mathematician’s research, considering the resources he had at the time: “I don’t think you can rate this achievement highly enough.” (Feehalberstadt)
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