Eratosthenes o Cyrene (/ɛrəˈtɒsθənz/; Greek: Ἐρατοσθένης, IPA: [eratostʰénɛːs]; c. 276 BC[1] – c. 195/194 BC[2]) wis a Greek mathematician, geografer, poet, astronomer, an muisic theorist. He wis a man o learin, acomin the chief leebrarian at the Leebrar o Alexandria. He inventit the discipline o geografie, includin the terminology uised the day.[3]

An etchin o a man's heid an neck in profile, leuking tae the richt. The man haes a beard an is baldin.
Born276 BC
Died194 BC
  • Scholar
  • Librarian
  • Poet
  • Inventor

He is best kent for bein the first person tae calculate the circumference o the Yird, that he did bi comparin angles o the mid-day Sun at twa places a kent North-Sooth distance apairt.[4] His calculation wis remerkably accurat. He wis an aw the first tae calculate the tilt o the Yird's axis, again wi remerkable accuracy.[5] Additionally, he mey hae accuratly calculatit the distance frae the Yird tae the Sun an inventit the leap day.[6] He creatit the first map o the warld, incorporatin parallels an meridians based on the available geografic knawledge o his era.

Eratosthenes wis the foonder o scienteefic chronology; he endeavoured tae revise the dates o the chief leeterar an poleetical events frae the conquest o Troy. Eratosthenes datit The Sack o Troy tae 1183 BC. In nummer theory, he introduced the sieve o Eratosthenes, an efficient method o identifeein prime nummers.

He wis a feegur o influence in mony fields. Accordin tae an entry[7] in the Suda (a 10t-century reference), his creetics scorned him, cryin him Beta (the seicont letter o the Greek alphabet) acause he ayeweys cam in seicont in aw his endeavors.[8] Nanetheless, his devotees nicknamed him Pentathlos efter the Olympians that war weel roondit competitors, for he haed pruiven himsel tae be knawledgeable in ivery aurie o learin. Eratosthenes yearned tae unnerstaund the complexities o the entire warld.[9]


  1. The Suda states that he wis born in the 126t Olympiad, (276–272 BC). Strabo (Geography, i.2.2), tho, states that he wis a "pupil" (γνωριμος) o Zeno o Citium (who died 262 BC), that wad implee an earlier year-o-birth (c. 285 BC) syne he is unlikely tae hae studied unner him at the young age o 14. However, γνωριμος can an aa mean "acquaintance", an the year o Zeno's daith is bi no means definite. Cf. Eratosthenes entry in the Dictionary of Scientific Biography (1971)
  2. The Suda states he died at the age o 80, Censorinus (De die natali, 15) at the age o 81, an Pseudo-Lucian (Makrobioi, 27) at the age o 82.
  3. Roller, Duane W. Eratosthenes' Geography. New Jersey: Princeton University Press, 2010.
  4. Ridpath, Ian (2001). The Illustrated Encyclopedia of the Universe. New York, NY: Watson-Guptill. p. 31. ISBN 0-8230-2512-8.
  5. "Eratosthenes (276 - 195 B.C.)". Cornell University. Accessed 28 Julie 2019.
  6. Alfred, Randy (19 Juin 2008). "June 19, 240 B.C.: The Earth Is Round, and It's This Big". Wired. Retrieved 22 Juin 2013.
  7. Entry ε 2898
  8. See also Asimov, Isaac. Asimov's Biographical Encyclopedia of Science and Technology, new revised edition. 1975. Entry #42, "Eratosthenes", Page 29. Pan Books Ltd, London. ISBN 0-330-24323-3. This was also asserted by Carl Sagan 31 minutes into his Cosmos episode The Shores of the Cosmic Ocean
  9. Chambers, James T. "Eratosthenes of Cyrene." Dictionary Of World Biography: The Ancient World (January 1998): 1–3.