The shape and size of the Earth

In the first, childish ideas, the earth is flat all around, from all sides washed by water, but already at the classical peoples, at least among scholars, gradually evolved belief in the sphericity of the Earth. With the names of Pythagoras, Parmenides, Archimedes, Ptolemy binds the thought of his first appearance. In the Renaissance of Sciences in the west this idea was resurrected, and a deep belief in the certainty of its forces Columbus to go on a long journey to the unknown West and find a new way to India and finally, the first trip around the world Magellan was undeniable and compelling evidence of the sphericity of the Earth. But this curiosity of a man was not yet satisfied: he set out to determine the magnitude of the globe. Already over 200 years before Christ. this important task by scientists whose work belong to the brilliant studies of antiquity and whose name in the history of science is surrounded with undying glory. This - Athenian Eratosthenes, the librarian at Alexandria. With the most insignificant means, exclusively guided by his genius, he first took measurements, which we now call the measure a degree meridian. Determine the magnitude of the Earth by measuring one of the great circles of her all over, of course, impossible to find astronomical by geographic location of the two seats and the distance between them to measure directly. Based on these data will be possible to calculate the magnitude of one degree. Eratosthenes measured the length of the shadows that cast on the ground perpendicular to the pole (gnomon) measurement was performed in Alexandria, the longest day of the year at about noon, it was already known that at the same time under the Tropic of Siena (now Aswan) in Upper Egypt, the sun is at its zenith, and so upright standing subject does not cast shadows. For these two data Eratosthenes found the distance between Alexandria and the Tropic is 7 ° 12 '. On the other hand, careful measurements taken by the Egyptian government, led to the direct determination of the distance between Alexandria and Siena, so were there any data to find the value of a degree meridian. According to the calculations of Eratosthenes, he is 700 stages, hence the circumference of the Earth = 700. 360 = 252 000 steps; Alexandria Stage 74 = 158 m; expressing Eratosfenom calculated value in today's action, we find that it = 5323 geogr. miles, this number is so little different from the true size of meridian (5400 miles), we can only wonder at the accuracy that has been reached so imperfect means. Of course, the result was correct, thanks to a fluke: the errors made in determining the latitude and distance measurement, cancel. Nevertheless, the striking closeness, the value found for the real causes could not help question the validity of posts Kleomeda, from which we learn that to determine the latitude of Alexandria Eratosthenes used only by measuring the shadows thrown gnomon.