#### Transcript of Eratosthenes

**Eratosthenes**

276 b.c - 195 b.c

made by Katelyn Ensinger

period 3

Information

Eratosthenes was born in Cyrene, Greece (which is now known as Libya, South Africa) in 276 B.C

He died in 195 B.C because he starved himself to death due to the fact that he became blind and could no longer work.

Careers/ hobbies

*Aside from being a mathematician, Eratosthenes was also a geographer, astronomer, histoarian and a poet.

*During this period of time ; the circumfrance of the earth was unknown- so many astronomeres were trying to figure it out, but it was Eratosthenes who figured it out. He figured out that the earths circumfrance was about 250, 000 miles long.

Educational Background

*Eratosthenes was sent to Athens to receive his education. While he was there he studied mathematics and philosophy at the famous Athenian academies.

*When he was in his thirties he was invited by Ptolemy III, the king of Egypt at that time, to come to Alexandria to tutor his son.

What he Invented

*He imvented the word 'Geography' which means 'Writing about the Earth'

*He drew a map of the world and made a star catologe of 675 stars.

*He developed the Sieve of Eratosthenes, which is a meathod of determing prime numbers up to any given limit.

What he invented cont.

Eratosthenes figured out that if you were to write down all the natural numbers from 2 to infinity and pick out/ seive out every second number after two ,then move to the next available number (3) and continue to "sieve out" every multiple of 3 and so on, one would end up with a list of prime numbers.

*Seive means 'to remove'.

How his invention is useful today

Prime numbers today are mainly used in Cryptography ( the art of writing or solving codes). So they are mainly used in computers to give them 'harder to crack codes' to try and prevent hackers and such from getting in.

"Why did you pick this person"

Honestly, the reason why I picked Eratosthenes is because he had the word "era" in his name. Also because he had a long name that would be difficult to pronounce, so it could be entertaining trying to figure it out.

"What did you learn?"

I learned the use of prime numbers! I never knew what they were for or why they were here or anything like that, so learning their use was interesting.

Bibliography

*http://www.odec.ca/projects/2007/fras7j2/uses.htm

*http://www.math.wichita.edu/history/men/eratosthenes.html

*http://www.saburchill.com/HOS/astronomy/005.html

Full transcript