Lecture 4: Measuring the Earth

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.