Eratosthenes
Mathematician,
Geographer, Astronomer
276 BC- 194 BC
• 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
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.
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.
Contributions: Sieve
The Sieve of Eratosthenes is a way to find
prime numbers. Eratosthenes's method:
1. Take the square root of the integer you
want to check and round it to the nearest
whole number
2. List all numbers smaller than the integer
and delete all even numbers
3. Check numbers up to the rounded square
root to see if the rest of the numbers in the
list are prime
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 = 23.855º
Contributions Not Preserved
• Map of the Nile
• Star catalogue containing 675 stars
• Poem “Hermes” about Astronomy
Bibliography
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•
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http://en.wikipedia.org/wiki/Eratosthenes
http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Eratosthenes.html
http://astrosun2.astro.cornell.edu/academics/courses//astro201/eratosthenes.htm