Eratosthenes of Cyrene
Sciences & Discovery • Historical Archive • 🇱🇾 Libya • 9 views

Eratosthenes of Cyrene 🇱🇾

Ἐρατοσθένης ὁ Κυρηναῖος (Known as "Father of Geography")
Chief Librarian of Alexandria, Mathematician, Geographer, Astronomer
Born c. 276 BCE 🇱🇾 Cyrene (Shahhat), Libya
Passed Away c. 194 BCE Alexandria, Egypt
Lifespan ~82 years old
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Notice / Correction
"The measurement of the earth reveals the harmony of the cosmos through the shadows of geometry."

Archival Overview

Chief Librarian of the Great Library of Alexandria who calculated the Earth's circumference with astonishing accuracy using sun shadows and invented the Sieve of Eratosthenes for prime numbers.

Biographical Record

Eratosthenes of Cyrene (c. 276–194 BCE) was appointed by Pharaoh Ptolemy III Euergetes to head the Great Library of Alexandria. A true polymath, he coined the term 'geography' (*geographia*) and mapped the known world with precise latitude and longitude grids.

By comparing the noon shadow of the summer solstice at Syene (Aswan), where the sun shone directly down a deep well, with the angle of a shadow cast in Alexandria (about 7.2 degrees), he calculated the circumference of the Earth to within a fraction of modern satellite measurements. In mathematics, he devised the famous algorithmic sieve for identifying prime numbers.

Key Life Milestones

c. 240 BCE

Calculation of the Earth's Circumference

Measured the Earth's meridian circumference to approximately 250,000 stadia using sun angles at Syene and Alexandria.

c. 235 BCE

Invention of the Sieve for Prime Numbers

Created the foundational mathematical algorithm for systematically filtering prime numbers from composite integers.

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Final Resting Place

Perpetual Memorial
Royal Quarter of Alexandria Memorial
Alexandria, Egypt
GPS: 31.2001, 29.9187
View on Memory Atlas
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