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Hipparchus was born around 190 BC in a town called Nicaea, in what is now Turkey. Later he spent time in Alexandria, near the famous library, and on the island of Rhodes. Today Hipparchus is most famous as an astronomer. He made many measurements and maps of the sky. He also studied trigonometry and was the first Greek philosopher to divide the circle into 360 degrees.

Hipparchus wrote many books about the things he studied. One of his books was called Against the Geography of Eratosthenes. In this book, Hipparchus criticized Eratosthenes' grid system. Hipparchus thought Eratosthenes' grid was arbitrary: the reference lines were set down without any consideration of the shape of the earth. Hipparchus used his knowledge of trigonometry and angles to suggest a different system. He measured distances in degrees north and south of the equator, and east and west of a reference line through Rhodes. Except for the fact that his reference line was through Rhodes, Greece, and not through Greenwich, England, Hipparchus' system was just like the system of latitude and longitude we use today.


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