Who was the first to measure the Circumference of Earth?

Question

Who among the old Greek Philosophers/Scientists was the first to measure the Circumference of Earth?

Answer 1

Erasthenes of Cyrene.  Actually Cyrene is not in Greece, it's in North Africa.  He's the same guy who invented the 'sieve of Erasthenes' which you would be familiar with if you ever took a beginning course in computer programming.

Erasthenes played around with gnomons.  A gnomon is basically a stick in the ground.  The stick casts a shadow based on the position of the sun, and you can learn about the relative movements of the sun and earth by tracing the path of the end of the shadow.  By doing this, then moving a specified distance and doing it again, Erasthenes came up with a diameter for the earth that was more accurate than anyone would have for more than 1000 years.  Columbus thought he had reached India because he greatly underestimated the distance because he had bad data on the circumference of the earth.  Erasthenes could have helped him!

Answer 2

It was Eratosthenes:

http://en.wikipedia.org/wiki/Eratosthene...

Answer 3

God  ... He wanted it a little bigger but took a day off and this is what we got.

Answer 4

Eratosthenes, in Egypt under the Ptolemies.

He knew the distance between Alexandria (where he lived) and Syene (the modern Aswan) and he knew that the direction between them was pretty close to north-south. He had heard that on the summer solstice, a verticle stick cast no shadow at noon, so he knew that Syene was on the Tropic of Cancer. On the same day and time, he measured the altitude of the sun at Alexandria and thus knew the latitude of both places. It was then simple trigonometry to use the distance between them to calculate the circumference of the earth.

Answer 5

Copied from "rhsaunders"

A chap named Eratosthenes. He was the curator of the great library at Alexandria about 250 BC. While traveling in the south of Egypt one summer at the town of Syene (now Aswan), he noticed that the midday sun at the solstice shone directly down a well, illuminating the bottom. He had noticed that this did not happen at home. He measured the distance between Syene and Alexandria, and noted that at Alexandria the sun was off vertical by 7.2 degrees - 1/50 of a circle. Multiplying the distance from Syene to Alexandria by 50, he came up with a number which was nearly correct. We don't know exactly how close he was, because the exact length of his unit of measurement has been lost. But his method was sound and his measurement was good.