Question

How was the size of earth first measured?

Answer 1

Eratosthenes an Egyptian mathematician was first to estimate Earths circumference. about 2200 years ago.

Explanation:

He found that on summer solstice day Sun was visible in a deep well..He knew that on the same day in his hone town that day Sun made a n angle. THe town was about 800 KM from the place were the well was located. He measured the shadow the sun made on a vertical stick tio be 7.2 degree.
So the angle 7.2 for 800 kilometers.
The cities were Syene and Alexandrai

Angle 7.2 degree was 1/50th of 360 degree. So total will be 800 x 50=40,000 kilometers.
He used different units at that time.But we consider kilometers in equivalent size.
Picture credit Geohunter cunny edu.