What is erasthosthenes?

Answer 1

Eratosthenes was a Classical Greek mathemtician, who lived in Alexandria, Egypt.

He was the first person to theorise that the Earth is spherical.

He sent a friend to Syene(Aswan), which is approximately 500 miles ( a circular arc) due south of Alexandria. He asked his friend to dig a big hole, and measure the angle of shadow on the longest day. The angle was found to be zero (no shadow ; Sun directly overhead). He did the same at Alexandria on the same day , and found a shadow of 7.5 degrees.

From this and knowing the arc length (500 miles) and the two angles 0 degrees and 7.5 degrees. , and using the circle equation ( C = 2 pi r)

He was able to calculate the Earth's circumference to a high degree of accuracy.

Have look in Wikipedia under 'Eratosthenes' . It will give a diagram of Earth's circular measure.

All this occured some 1500 yers before Columbus proved tha fact by making a voyage to the Americas.

Answer 2

Eratosthenes of Cyrene was a Greek mathematician, geographer, poet, astronomer, and music theorist.