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Eratosthenes

Eratosthenes
An etching of a man's head and neck in profile, looking to the right. The man has a beard and is balding.
Born 276 BC
Cyrene
Died 194 BC
Alexandria
Occupation
  • Scholar
  • Librarian
  • Poet
  • Inventor
Known for Sieve of Eratosthenes

Eratosthenes of Cyrene (/ɛrəˈtɒsθənz/; Greek: Ἐρατοσθένης ὁ Κυρηναῖος, IPA: [eratostʰénɛːs]; c. 276 BC – c. 195/194 BC) was a Greek mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandria. He invented the discipline of geography, including the terminology used today.

He is best known for being the first person to calculate the circumference of the Earth, which he did by applying a measuring system using stadia, a standard unit of measure during that time period. His calculation was remarkably accurate. He was also the first to calculate the tilt of the Earth's axis (again with remarkable accuracy). Additionally, he may have accurately calculated the distance from the Earth to the Sun and invented the leap day. He created the first map of the world, incorporating parallels and meridians based on the available geographic knowledge of his era.


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