Eratosthenes

Eratosthenes of Cyrene (/ɛrəˈtɒsθəniːz/; Greek: Ἐρατοσθένης, 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, which was 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 geographical knowledge of the era.

Eratosthenes was the founder of scientific chronology; he endeavored to revise the dates of the chief literary and political events from the conquest of Troy. In number theory, he introduced the sieve of Eratosthenes, an efficient method of identifying prime numbers.

Eratosthenes (statesman)

Eratosthenes of Athens (Greek: Ἐρατοσθένης) was one of the Thirty Tyrants elected to rule the city of Athens after the Peloponnesian War (431–404 BC).

Having lost the war to the Spartans, the citizens of Athens elected thirty men as oligarchs. The Thirty instituted oppressive and highly exclusionary laws and instituted a political purge against Athenians who had been Spartan informers and collaborators during the long war. Eventually open hostilities between the Thirty and disenfranchised or disaffected Athenian citizens led to a coup d'etat in 403 BC that deposed them.

He is the subject of a legal oration by the orator Lysias, entitled Against Eratosthenes (Speech 12). According to some critics he is also the subject of another of Lysias' speech, On the Murder of Eratosthenes (Speech 1). However, the age of the Tyrant does not fit with the context of the latter speech: he must have been aged at least 18 in 411 BC to have served as a trierarch, and at least 30 by the time of the Thirty Tyrants period in 403/2 BC. But On the Murder of Eratosthenes suggests that the Eratosthenes referred to in that speech was younger than 30 at the time of his death – he is described as 'neaniskos', a word which Lysias elsewhere uses to refer to younger men.

Eratosthenes (disambiguation)

Eratosthenes may refer to: