Humanities › History & Culture The Greek Mathematician Eratosthenes Share Flipboard Email Print Public Domain. Courtesy of Wikipedia. History & Culture Ancient History and Culture Figures & Events Ancient Languages Greece Egypt Asia Rome Mythology & Religion American History African American History African History Asian History European History Genealogy Inventions Latin American History Medieval & Renaissance History Military History The 20th Century Women's History View More By N.S. Gill Ancient History and Latin Expert M.A., Linguistics, University of Minnesota B.A., Latin, University of Minnesota N.S. Gill is a Latinist, writer, and teacher of ancient history and Latin. She has been featured by NPR and National Geographic for her ancient history expertise. our editorial process N.S. Gill Updated January 14, 2020 Eratosthenes (c.276 to 194 B.C.), a mathematician, is known for his mathematical calculations and geometry. 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 is the calculation of the circumference of the earth and the development of a mathematical sieve named after him. He made a calendar with leap years, a 675-star catalog, and maps. He recognized the Nile's source was a lake, and that rains in the lake region caused the Nile to flood. Eratosthenes: Life and Career Facts Eratosthenes was the third librarian at the famous Library of Alexandria. He studied under the Stoic philosopher Zeno, Ariston, Lysanias, and the poet-philosopher Callimachus. Eratosthenes wrote a Geographica based on his calculations of the circumference of the earth. Eratosthenes is reported to have starved himself to death at Alexandria in 194 B.C. Writing of Eratosthenes Much of what Eratosthenes wrote is now lost, including a geometrical treatise, On Means, and one on the mathematics behind Plato's philosophy, Platonicus. He also wrote the fundamentals of astronomy in a poem called Hermes. His most famous calculation, in the now lost treatise On the Measurement of the Earth, explains how he compared the shadow of the sun at Summer Solstice noon in two places, Alexandria and Syene. Eratosthenes Calculates the Circumference of the Earth By comparing the shadow of the sun at Summer Solstice noon at Alexandria and Syene, and knowing the distance between the two, Eratosthenes calculated the circumference of the earth. The sun shone directly into a well at Syene at noon. At Alexandria, the angle of inclination of the sun was about 7 degrees. With this information, and knowing that Syene was 787 km due south of Alexandrian Eratosthenes calculated the circumference of the earth to be 250,000 stadia (about 24,662 miles).