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Eratosthenes: Earth
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Eratosthenes was an important mathematical figure of ancient Greece. Among his accomplishments was the accurate measurement of the earth's circumference. He ... wrote works on mathematics, geography, philosophy, and astronomy. Although many of his works have been lost, historians have uncovered a substantial amount of information about important events in his life and his accomplishments.
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Eratosthenes' estimate was the most accurate in ancient times, and the climactic feat of the ancient practical art of geometry, or earth measurement. Yet his contemporaries thought of him as a second-string man," for around the same time, and in the same city of Alexandria, there lived another geometer whose name is more widely known than any mathematician's in history.
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The World Year of Physics project "Measure the Earth with Shadows," commemorates Eratosthenes' many outstanding accomplishments by giving high school students a chance to duplicate the brilliant scientist's most famous experiment, on the largest scale ever attempted. In 2005, participating students will use shadows to measure the position of the sun at high noon. By comparing their measurements with those of students at other latitudes, they will be able to calculate the size of the Earth, just as Eratosthenes did more than two thousand years ago.
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When Eratosthenes returned to Alexandria, being a good astronomer, he knew he could wait until next year on the first day of summer and measure the altitude of the noon sun. Then since he had kept track of how far he had traveled from Syene to Alexandria, he could determine the circumference and the diameter of the earth.
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Eratosthenes is ... known as a great geographer. He sketched the route of the Nile and suggested that its source is in lakes, and that the floods lower on the river occur when heavy rainfall hits those lakes. He was the first one to get this essentially right answer, even though many scientists of his time had worked on this problem. Eratosthenes also divided the Earth with lines going north, south, east, and west.
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Eratosthenes was called "Beta" (the second letter of the Greek alphabet) because he was never first, but he is more famous than his "Alpha" teachers because his discoveries are still used today. Chief among these are the calculation of the circumference of the earth (note: the Greeks did know the earth was spherical) and the development of a mathematical sieve named after him. He made a calendar with leap years, a 675-star catalogue, and maps. He recognized the Nile's source was a lake, and that rains in the lake region caused the Nile to flood.
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