# Earth radius: interesting facts

To date, the length of the equator and the meridian are determined fairly accurately. Fortunately, science has reached such a level of development that now it’s easy to find out the basic parameters of any celestial body. However, the story contains many interesting facts about how the first important discoveries were made. In particular, we will tell about how people learned that, on average, the Earth’s radius is 6,371 kilometers.

Who first made the calculations?

Many discoveries are made by virtue of great curiosity and curiosity. These qualities were inherent in man at all times, and, at least, in their absence it was impossible to reproach the ancient Greek Eratosthenes of Kirensk. This pundit became famous as a talented mathematician, geographer, astronomer and poet, as well as the first person who determined the radius of the Earth. It happened around 240 BC. One day, Eratosthenes, who worked in the Library of Alexandria, found a papyrus, which reported an interesting observation by the Egyptians.It was said that in the southern part of Egypt, in Siena (now this city is known as Aswan), on June 21, exactly at noon, a vertical pole set to the earth’s surface ceases to cast a shadow, and the sun’s rays reach the bottom of the deepest wells. In other words, the sun is directly overhead. Curious Eratosthenes decided to check this information in Alexandria, for which, having waited on June 21, he conducted a similar experience with the sixth.

And what do you think? The shadow of the pole was. Our contemporary in his place, most likely, would have shrugged his shoulders and decided that the Egyptians had messed up or slightly exaggerated, and would continue to go about their daily business. But Eratosthenes did not give up so easily: he measured the length of the shadow and, on reflection, came to the conclusion that the earth's surface was curved. In fact, if it were flat, the sunlight on the same day would fall everywhere at the same angle. Having decided to test his guesses, the Greek hired one person to calculate the number of steps from Alexandria to Siena. Thus, he was able to make calculations and found out that the radius of the Earth is 40,000 stages. If you translate this value in kilometers, you get 7000 km.Surprisingly, given the method of determination, the error was only 629 km - at that time it was quite accurate.

Modern Theories

Despite the fact that the average equatorial radius of the Earth (6378.137 km), the radius of the orbit, the distance to the Sun and other parameters of our planet are now calculated with very high accuracy, scientists are not in a hurry to completely switch to space exploration.In particular, in the XIX century a curious hypothesis was put forward regarding the factors that influenced the formation of mountains and oceans. Scientists have suggested that the probable cause was the radius of the Earth’s orbit changing as a result of the displacement of tectonic plates. Until recently, many researchers adhered to this point of view, and only recently (in 2011), the results of a new study conducted by specialists of the Jet Propulsion Laboratory, completely refuted this hypothesis. Experts have built a detailed model of the movement of geographical objects on the earth's surface, focusing on the data obtained using satellites. It turned out that even if the radius of our planet changes, the rate of such a change in a year does not exceed 1/10 of a millimeter.