Who was the African genius who proved that the Earth was round using a stick 2,000 years ago?
Eratosthenes of Cyrene (276 BC-194 BC) based his theory on the summer solstice, as well as on a scientific manuscript from the Library of Alexandria.
Born in the ancient city of Libya, Eratosthenes of Cyrene (276 BC-194 BC) was able to calculate the diameter and circumference of the Earth without the help of high-tech tools. He was a mathematician, astronomer, geographer, historian and philosopher, among other professions, and received the nickname Pentathlos.
The scientist calculated what the axis of inclination of our planet was. To do this, he used a stick perpendicular to the ground on the summer solstice, in order to measure the length of the shadow that the instrument cast on the ground at noon. The result, a shadow of seven degrees. It was an experiment that he carried out in Alexandria, and that he could not demonstrate in Siena (present-day Aswan, in southern Egypt). At noon and during the summer solstice, there were no shadows there.
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Flat earth dispelled
At that time, he already deduced that the Earth was round. To carry out the calculation of the circumference, he studied the existing distance between Siena and Alexandria by means of the time it took to cover the distance traveled by the camels. In a straight line, the distance between the two cities was 5,040 stadia, or 800 kilometers. With this, he established the following direct relationship. If the seven degrees of difference are equivalent to 800 kilometers, the 360 degrees of the Earth are about 39,750 kilometers; that is, close to the 40,000 kilometers that the circumference of the planet measures.
Eratosthenes: Nearly accurate calculations
He became the first person to establish for the first time the circumference of the Earth with a margin of error of just 90 kilometers, compared to the current size estimated by scientists. Eratosthenes lived for most of his life in Athens until he later moved to Alexandria in 245 BC. to educate the children of Ptolemy III, and to direct the city library.
In addition to his knowledge of the dimensions of our planet, in the field of mathematics he was known for creating the so-called Eratosthenes Sieve, which made it possible to obtain prime numbers. Another of the reasons why this mathematician is remembered was for the creation of the armillary sphere, which is an astronomical instrument used in Antiquity and the Middle Ages to determine the position of celestial bodies.
Earth dimensions
As for its current characteristics, the Earth has an inclination of 7.155°, that is, very similar to that projected by Eratosthenes. Its average orbital speed is about 29.78 km/s, or 107,200 km/h. Formed 15 billion years ago, its distance from the Sun is 150 million kilometers. The diameter that passes through the poles is 12,714 kilometers.