How did Eratosthenes measure the circumference of the earth? - Answers

HERE ARE SOME SITES YOU MIGHT WANT TO TAKE A LOOK AT... WITH A SHORT DESCRIPTION OF WHAT INFORMATION IT HAS ON THE WEBPAGE. * http://en.wikipedia.org/wiki/Eratosthenes- This is the Wikipedia page for Eratosthenes. It has a lot of information about him as well as how he measured the circumference of the Earth. It also lists reasons why Eratosthenes's calculation of the Earth's circumference has limited accuracy. * http://www.juliantrubin.com/bigten/eratosthenes.html - This site has all the information about how Eratosthenes measured the circumference of the Earth. It has a diagram to illustrate and explain further. This site also lists other sites and books relating to the math topic. * http://outreach.as.utexas.edu/marykay/assignments/eratos1.html - This is a webpage with information on how to do an activity related to Eratosthenes and his calculation of the Earth's circumference. It has some diagrams, some that show how Eratosthenes measured it, and some show real-world examples of how you can calculate the Earth's circumference just like Eratosthenes. Along with the drawing, this webpage has instructions on how you can measure the circumference of the Earth in real-life situations. * http://www.astro.cornell.edu/academics/courses/astro201/eratosthenes.htm - This webpage shows how the Earth's circumference was measured by Eratosthenes using geometry. It has a nice, easy-to-understand diagram to further explain Eratosthenes's calculation. The information on the webpage is probably very reliable since it's from a university. * http://mathforum.org/library/drmath/view/58988.html - This webpage is from Dr. Math's website. It has a very detailed explanation of how Eratosthenes measured the circumference of the Earth. There are no diagrams though. * http://eduwww.mikkeli.fi/opetus/myk/kv/comenius/erathostenes.htm - This webpage has a short summary of Eratosthenes's life. It has information on how the sieve of Eratosthenes, another thing Eratosthenes worked out in during his lifetime, worked. This page also has a lot of information about Eratosthenes and his calculation of the Earth's circumference, with a couple of drawings to make it easier to understand. * http://maps.unomaha.edu/Peterson/carta/Notes/eratosthenes.html - This website has a short biography of Eratosthenes and also how he measured the circumference of the Earth. The explanation is very detailed and easy to understand even without the support of diagrams. This site has a .edu in the address, so I think it will be very reliable. * http://www.pbs.org/wnet/hawking/cosmostar/html/cstars_eratho.html - This PBS webpage has a short summary of Eratosthenes's life. This webpage has a little bit of information of Eratosthenes measure of the circumference of the Earth. It also tells how other great mathematicians, like Posidonius and Ptolemy, tried to measure the circumference of the Earth.