What is the diameter of the Earth and how did you first measure it? The discovery of Eratosthenes was undoubtedly an achievement if we consider that he was able to measure the diameter of our planet in the year 240, but how did he do it? Keep reading that we explain it to you below.
What is the diameter of the Earth and how did you first measure it? The discovery of Eratosthenes
What would you do with a well, a stick, and a camel? The philosopher Eratosthenes of Cyrene (276 BC -194 BC) used them to measure, more than two thousand years ago, the circumference of the Earth.
At that time there was already awareness that the Earth was spherical , and Eratosthenes learned that on the day of the summer solstice (June 21), in the city of Siene in southern Egypt (today Aswan), the Sun, at noon , was reflected in the waters of a deep well ; the Sun, therefore, was exactly perpendicular to the well and a stick planted in the ground produced no shadow.
On the same day that it shone at the well of Siena, the Sun was not perpendicular to Alexandria , the city where Eratosthenes lived, and where, therefore, a stick planted perpendicular to the ground cast a shadow , albeit a small one. Eratosthenes measured the angular distance of the sun with respect to the point where it should have been in order not to cast any shadow even in Alexandria and estimated this distance at 7.2 degrees, that is, one fiftieth of a circle, out of 360 degrees.
To identify the circumference of the earth, it only remained to measure the distance between the two cities … but at that time there were no navigators or satellite odometers, but yes … camels . These animals had an almost constant gait that covered an average of about 100 stages per day, and since a caravan took 50 days to travel the distance was about 5000 stages, equivalent to the length of a sports stadium , and it was also the unit distance used in Greece.
To get the circumference of the Earth all that was left was to multiply 5000 stadia (the distance between the two cities) by 50 (7.2 ° by 50 is 360 °, therefore a “circumference”) and this multiplication results in 250,000 stadia. which, translated into km, is equivalent to a variable value between 39,690 km and 46,000 km depending on the different definitions of stadium present among the old sources but, in any case, very close to the real value, which is about 40,000 km.
Curiosities about the measurement of Eratosthenes
The results of Eratosthenes were known by the commission of experts appointed by the King of Spain Ferdinand to examine Columbus’s proposal to finance the trip to the Indies . The experts rejected Columbus’s proposal precisely because, using the original value of Eratosthenes, they concluded that the distance was too great. However, Queen Elizabeth overruled the opinion of the experts and the rest is history.
On the other hand , Eratosthenes was also director of the royal library of Alexandria , the largest and most famous library of antiquity. Officially, the library was called “the Temple of the Muses,” hence our modern term “museum.”
