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'''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]].

== Biography ==

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 number|prime number]]s.

He was a figure of influence who declined to specialize in only one field.

According to an entry in the [[Suda]] (a 10th-century reference), his critics scorned him, calling him ''Beta'', from the second letter of the Greek alphabet, because he always came in second in all his endeavors.

Nonetheless, his devotees nicknamed him ''Pentathlos'', after the Olympians who were well rounded competitors, for he had proven himself to be knowledgeable in every area of learning.

Eratosthenes yearned to understand the complexities of the entire world.

== See also ==

* [[Astronomical unit]]
* [[Early world maps]]
* [[Sieve of Eratosthenes]]

== External links ==

* [https://en.wikipedia.org/wiki/Eratosthenes Eratosthenes] @ Wikipedia



[[Category:Astronomers]]
[[Category:Geographers]]
[[Category:Mathematicians]]
[[Category:Music theorists]]
[[Category:Poets]]