Greek Mathematician Eratosthenes measured the circumstance of the Earth in 240 B.C.
He put two vertical sticks of the same length in the ground and measured their shadows in Alexandria and Syene that were 800km apart at the same day and time.
The shadow was absent in Alexandria. The shadow corresponded to angle of 7.2° in Syene.

Based on the information can you calculate the circumstance of the Earth?