What is the shape and size of the Earth? This lecture traces historical

ideas about the shape of the Earth, from ancient flat-Earth models to

the compelling demonstrations by Aristotle in the 3rd century BC that

the Earth was a sphere. We then discuss ways people measured the size

of the Earth, describing the results of Eratosthenes of Cyrene in the

2nd century BC and Claudius Ptolemy in the 2nd century AD, and their

impact. Recorded 2006 Sep 25 in 100 Stillman Hall on the Columbus

campus of The Ohio State University.