Truth is, we (mankind) have been making maps and studying the size and shape of the earth for hundreds of years. To begin with, we were concerned with the area around our homes, and later, as we traveled farther from home, our interest grew to include larger and larger areas. The size of the world we lived on began to be of interest.

The early Greek mathematicians and thinkers such as Homer, Plato and Pythagoras all had ideas on the shape and size of the earth. While a few thought the earth to be flat (One guy even thought the earth was rectangular in shape!) most agreed that the earth was round or 'spherical'.

Support for the 'round earth' theory came from the sailors of ancient Greece. They noticed that as they approached their home port they could see only the high points. As they got closer, the land appeared to 'rise' from the sea.

The Greeks made many estimates of the size of the earth. These estimates were pretty good for the times, but were guesses all the same.

Eventually, one curious fellow had an idea about how he could not only prove the earth was round, but measure the size as well.

His name was Eratosthenes. (Pronounced like "Era tossed the knees"). He was a Greek mathematician and while he was living and working in Egypt he came up with an idea to make a more accurate measurement of the size of the earth.

Eratosthenes wondered if a second stick stuck in the sand in a different place would cast a shadow. If the second stick cast a shadow, then the earth could not be flat (as some presumed) but must be round. Knowing what he did about mathematics (mathematics does come in handy every now and again!), he figured out that if he could measure the distance between the two sticks, and the shadow cast at the second stick, he could work out the size of the earth. He'd be famous!

Eratosthenes raced off to Alexandria, 800 km away and placed a second stick in the sand. Sure enough, this time the sun cast a shadow.

Eratosthenes measured the shadow and using the distance between the two sticks figured the earth's circumference to be 40,234 km (25,000 miles). The currently accepted value for the earth's circumference at the Equator is 40,074 km (24,901 miles). A difference of only 160 km (99 miles)!

Eratosthenes lived in a place called Syene (now called Aswan). He noticed that on the longest day of the year (the summer solstice) when the sun reached it's very highest point in the sky, that a stick placed straight up and down in the sand did not cast a shadow. In fact, he looked down into a dry well and noticed that the midday sun shone straight to the bottom, and the walls of the well were in sunlight. It was as if the sun was directly overhead.

That's like guessing the size of a soccer pitch and missing by the width of 2 soccer balls.  Pretty amazing for guy who measured distances by how far his camel can travel in a day!