Eratosthenes
# Eratosthenes of Cyrene

### Born: 276 BC in Cyrene (now Shahhat, Libya)

Died: 197 BC in Alexandria, Egypt

**Eratosthenes** was born in Cyrene which is now in Libya. After studying in Alexandria and Athens he became the director of the Library in Alexandria.

He worked on geometry and prime numbers. He is best remembered for his prime number sieve which, in modified form, is still an important tool in number theory research.

Eratosthenes also made a surprisingly accurate measurement of the circumference of the Earth. He compared the noon shadow in midsummer between Syene (now Aswan) and Alexandria. He gave the circumference of the Earth as 250000 stadia, the distance to the sun as 804000000 stadia and the distance to the Moon as 780000 stadia.

He measured the tilt of the Earth's axis with great accuracy obtaining the value of 23 51' 15". He compiled a star catalogue containing 675 stars.

Eratosthenes became blind in his old age and is said to have committed suicide by starvation.

**References (15 books/articles)**

**References elsewhere in this archive:**

Tell me about the sieve of Eratosthenes

Tell me about Eratosthenes' part in the longitude problem

There is a **Crater Eratosthenes** on the moon. You can see a list of lunar features named after mathematicians.

**Other Web sites:**

Kansas, USA

JOC/EFR December 1996