1. Mathematician, Geographer, Astronomer 276 BC- 194 BC
Eratosthenes
Mathematician, Geographer, Astronomer
276 BC- 194 BC

2. Born in Cyrene; Died in Alexandria
Known under the name β (Beta) because he was considered to be the second most knowledgeable person in the world on many subjects

3. Contributions: Earth’s Circumference
Around 240 BC, at noon on the summer solstice, Eratosthenes measured the altitude of the sun in Alexandria and Syene. He concluded that the circumference of the Earth was 252,000 stadia or 42,000 km.

5. Contributions: The First Globe
In 255 BC, Eratosthenes created the Armillary Sphere. It was what we would now call a globe. Eratostenes’ version had a large ball in the center representative of the Earth.

6. Contributions: Sieve
The Sieve of Eratosthenes is a way to find prime numbers. Eratosthenes's method:
Take the square root of the integer you want to check and round it to the nearest whole number
List all numbers smaller than the integer and delete all even numbers
Check numbers up to the rounded square root to see if the rest of the numbers in the list are prime

7. Other Contributions
Measured distance from Earth to the Sun and to the Moon during a lunar eclipse:
Earth → Sun = 804,000,000 stadia
Earth → Moon = 780,000 stadia
Measured tilt of the Earth’s axis
11/83 of 180 = º

8. Contributions Not Preserved
Map of the Nile
Star catalogue containing 675 stars
Poem “Hermes” about Astronomy

9. Bibliography http://en.wikipedia.org/wiki/Eratosthenes