# Tweet by [@keefmoon](http://twitter.com/keefmoon) on 2019-09-15 07:38:44 > [!INFO] Archived from [original tweet](http://twitter.com/keefmoon/status/1173139069125238784) RT @wonderofscience: Carl Sagan explains how the ancient Greeks knew the Earth was round and calculated its circumference over 2,000 years…