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Eratosthenes
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Eratosthenes (276-197 BC) was born in Cyrene (now Shahhat, Libya). After studying in Alexandria and Athens he became the director of the Library in Alexandria. (The Library at Alexandria, while functioning as what we think of as a library today... had elements of what we think of as a research laboratory.) He is best known for his accurate calculation of the Earth's circumference, within 15% of the modern day value, and this work is often referenced in introductory astronomy textbooks. One of the great beauties of his observation and measurement is the combination of clever insight, or the "Aha moment" and careful measurement. The "Aha moment" is in his realization that since the rays of the Sun striking the Earth can be taken as parallel, that on any given day the solar zenith angle at solar noon of a point, A, on the Earth is the same size as one with its vertex at the center of the Earth with one ray pointing to point A and the other pointing directly to the Sun (i.e. the point on the Earth where the Sun is at the zenith, the overhead point O on diagram).
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Eratosthenes was born around 276 B.C.E. at a Greek colony in Cyrene, Libya. He was educated at the academies of Athens and was appointed to run the Great Library at Alexandria in 240. While serving as head librarian and scholar, Eratosthenes wrote a comprehensive treatise about the world, called Geography. This was the first use of the word, which literally means "writing about the earth" in Greek. Geography ... introduced the climatic concepts of torrid, temperate, and frigid zones.
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