Eristothenes measured the circumference of the earth by measuring the shadow of two poles, miles apart, at the exact same time. So how did he know the poles were being measured at exactly the same time in an era when people used the sun for timekeeping?

Question

Eristothenes measured the circumference of the earth by measuring the shadow of two poles, miles apart, at the exact same time. So how did he know the poles were being measured at exactly the same time in an era when people used the sun for timekeeping?

In: Mathematics

Answer 1

He didn’t. And he didn’t have to.

North of the tropics, the tip of an object’s shadow is the furthest south at the moment of solar noon. All you have to do is trace the path of the tip of the shadow and note where it is the furthest away.