When and how did scientists measure the radius of the earth?

In 200 B.C., the size of the earth was actually calculated. Eratosthenes used the Angular Displacement method to find the size of the earth and he used the methods of Aristotle’s idea.

The diameter of the earth at the equator is 12,756 Km. in modern times we have developed technologies that can measure it in seconds. But in ancient times, there was no such technology and the ancient methods were used by our great scientists. One of those was Eratosthenes who used the old technique to find out the radius of the earth. He has known the facts that in summers, the first day of summer the Sun passed directly overhead at Syene, Egypt. And on the same day in mid-time of the day he measured the angular momentum of the Sun from the overhead at the city of Alexandria which was 5000 stadia away. He found with the angular displacement that there is 7.2 angular displacement and at last he calculated the circumference of the earth was 40,000.

Eratosthenes also knows the fact that the circumference is equal to the two times the multiplication of the pie and radius. And hence with the help of these formulae, he inferred that the earth’s radius was 6,366 Km. the interesting fact is that this distance is approximately matching the modern distance of radius as the circumference is 40,070 and the radius is 6,376 km and it is measured by the spacecraft using the orbit of the earth.

The radius of the earth in its equator is 6,378 Km and but in another case in the polar of the earth is 6,357 Km.

The average distance from the Sun is 149,598,262 Km.

The perihelion is 147,098,291.

The aphelion of the earth is 152,098,233.

The length of the solar day is 23.934hrs

The length of the year in the earth is 365.26days.

The inclination of the equatorial is 23.4393 degrees.