Eratosthenes Measures the Earth Over 2200 years ago Eratosthenes read in the Alexandria li...

Eratosthenes Measures the Earth Over 2200 years ago Eratosthenes read in the Alexandria library that at noon on June 21 a vertical stick in Syene cast no shadow. So on June 21 at noon Eratosthenes set out a vertical stick in Alexandria and found an angle of 7° in the position shown in the drawing. Eratosthenes reasoned that since the sun is so far away, sunlight must be arriving at the earth in parallel rays. With this assumption he concluded that the earth is round and the central angle in the drawing must also be 7°. He then paid a man to pace off the distance between Syene and Alexandria and found it to be 800 km. From these facts, calculate the circumference of the earth (to the nearest kilometer) as Eratosthenes did and compare his answer with the circumference calculated by using the currently accepted radius of 6378 km.

Figure