Eratosthenes?

Question

Please help. I need to write a scientific report on Eratosthenes method for finding the diameter of the earth. I've been on wikepedia just help help help me.

Answer 1

Look for references for Eratosthenes, Syene, and Alexandria. He knew that when the sun was directly overhead at Syene its shadow made a certain angle at Alexandria. He also knew the distance between the two cities and figured that the earth was spherical. He then knew that the distance from Syene to Alexandria was a certain part of a complete circle, and multiplied the distance to get the circumference of the earth. He measured in units called stadia. Though it's not known exactly how long they were, it's believed today that he came up with an answer of about 25,000 miles, close to the actual value.

Answer 2

Eratosthenes lived in Alexandria Egypt. He knew of a well in the town of Syene where the suns rays went straight to the bottom on a certain day each year. He hired someone to walk between the two cities and record the distance.
On the day of the event he measured the angle of the suns rays to see how far they were from the vertical in Alexandria at the same time.
He assumed that angle in degrees when related to a circle had the same proportions as the distance around the globe would be to the distance from Alexandria to Syene. Plugging in his numbers to the proportion gave the answer.
The problem that we have with his work is that he used the unit of the "stadia". This was related to the size of the ancient race tracks found in those great cities. The problem is, they were not all the same size. As a result we don't really know what his results were in modern terms. Many sources state how 'accurate' his results were, but in truth, we really don't know.

Answer 3

As per Isaac and a point of interest on the unit of measurement, many scholars now believe he used base 20 math and not the base 10 we normally use now.