Who determined the circumference of the Earth and was keeper of the Library of Alexandria?

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Multiple Choice

Who determined the circumference of the Earth and was keeper of the Library of Alexandria?

Determining Earth’s circumference through simple geometry and observation, while also being the head librarian at the Library of Alexandria. Eratosthenes noticed that at noon on the solstice the sun was directly overhead in Syene (now Aswan), producing no shadow, while in Alexandria it cast a measurable angle. The angle between the two locations’ sun rays was about 7.2 degrees, which is roughly 1/50 of a full circle. If the distance between Syene and Alexandria was about 5,000 stadia, he concluded that the Earth’s circumference was 50 times that distance—about 250,000 stadia. Translating stadia into modern units gives roughly 39,000–40,000 kilometers, quite close to the real circumference. He also held the role of Librarian at the Library of Alexandria, a prestigious position in the Hellenistic world. The other figures are known for different contributions: Archimedes for mechanics and buoyancy, Aristotle for broad philosophical and scientific work, and Ptolemy for geography and astronomy, but Eratosthenes uniquely fits both the measurement achievement and the library leadership.

Determining Earth’s circumference through simple geometry and observation, while also being the head librarian at the Library of Alexandria. Eratosthenes noticed that at noon on the solstice the sun was directly overhead in Syene (now Aswan), producing no shadow, while in Alexandria it cast a measurable angle. The angle between the two locations’ sun rays was about 7.2 degrees, which is roughly 1/50 of a full circle. If the distance between Syene and Alexandria was about 5,000 stadia, he concluded that the Earth’s circumference was 50 times that distance—about 250,000 stadia. Translating stadia into modern units gives roughly 39,000–40,000 kilometers, quite close to the real circumference. He also held the role of Librarian at the Library of Alexandria, a prestigious position in the Hellenistic world. The other figures are known for different contributions: Archimedes for mechanics and buoyancy, Aristotle for broad philosophical and scientific work, and Ptolemy for geography and astronomy, but Eratosthenes uniquely fits both the measurement achievement and the library leadership.

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