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How did Eratosthenes know the Earth was round?

Greek philosopher Eratosthenes is said to have calculated the Earth's circumference in 240 BC. How did he do it? Was the Earth being round common knowledge at that time?

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Michael Scalise

Lvl 12
3y ago
Updated: 11/4/2022

Eratosthenes' method requires that one know or determine the vertical angle of the sun above the horizon or from the zenith (a point directly overhead) at solar noon at two locations along the same line of longitude. The distance between the two locations must also be known.

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Eratosthenes' method requires that one know or determine the vertical angle of the sun above the horizon or from the zenith (a point directly overhead) at solar noon at two locations along the same line of longitude. The distance between the two locations must also be known.

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Q: How did Eratosthenes know the Earth was round?
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How did Eratosthenes measure the circumference of the earth?

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.


Who said that the earth is a sphere?

Columbus said the earth was sphere when he traveled to America


Who was first mathematician to have measured the circumference of the earth?

Eratosthenes of Cyrene using shadows at two different places in Egypt. An amazing achievement for those times (about 200-250BC)


When did euratosthenes calculate the circumference of the earth?

It is not known when, or even if, Euratosthenes did calculate the circumference of the earth. However, it is known that a very accurate estimate was obtained by Eratosthenes in the early years of the third century BC.


What song has the lyrics up down round and round?

Who know maybe round and round by Selena gomez I don't know