We know that our Earth is massive and has a circumference of just over 40,000 kilometers. But spare a thought to how we actually found out this number. Did we measure it? Did we guess it? Is it an approximation? and when did we actually come to a conclusion about this number. We knew about this number well before we sent out rockets in the sky and high resolution cameras in space. Here is a short video explaining who calculated the Circumference of the Earth and How?