What is geodesy?

            Geodesy is the science of measuring the circumference of earth. When people came to know that the earth was round, they made use of geometry related to circles and angles. Nowadays, geodimeters can measure long distances very accurately by using light rays.

The traditional method used  by eratosthenes to calculate the circumstance of Earth

            The diagram shows how, in about 250 B.C., Eratosthenes measured the earth’s circumference. At noon in midsummer, the sun shone straight down a well at Syene, near Aswan in Egypt. At the same time in Alexandria, monument showed that the sun made an angle of 72 degrees.

            Using geometry, Eratosthenes knew that the angle at the centre of the earth would be the same. He calculated that the earth’s circumference was 46,300 kilometers.

            Eratosthenes was not very inaccurate in his measurements. In fact, the distance around the equator is 40,076 kilometers.

            Geodimeters are very useful and accurate devices for taking earth measurements.