In this photo taken Nov. 15, 2012, Peter Struck, Associate Professor of Classical Studies at the University of Pennsylvania prepares to record a lecture on Greek Mythology in

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In this photo taken Nov. 15, 2012, Peter Struck, Associate Professor of Classical Studies at the University of Pennsylvania prepares to record a lecture on Greek Mythology in Philadelphia. In 15 years of teaching, Struck has guided perhaps a few hundred students annually in his classes on Greek and Roman mythology through the works of Homer, Sophocles, Aeschylus and others — "the oldest strands of our cultural DNA." But if you gathered all of those tuition-paying, in-person students together, the group would pale in size compared with the 54,000 from around the world who, this fall alone, are taking his class online for free — a "Massive Open Online Course," or MOOC, offered through a company called Coursera. (AP Photo/Matt Slocum) less