Definitions
from The American Heritage® Dictionary of the English Language, 4th Edition
 Eratosthenes Third century B.C. Greek mathematician, astronomer, and geographer who devised a map of the world, estimated the circumference of the earth and the distance to the moon and the sun, and constructed a method for finding prime numbers.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
 n. Greek mathematician and astronomer who estimated the circumference of the earth and the distances to the Moon and sun (276194 BC)
Etymologies
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Examples

Fragment #38  'Eratosthenes' [1729], Catast.xix. p. 124: The

"This range curves round towards the east, and finishes with a fine ringplain called Eratosthenes  some thirtyseven miles in diameter, with a floor depressed 8000 feet below the lunar surface.

Eratosthenes accurately measured the radius of the Earth by determining the minimum angle between the Sun's direction and the vertical at Alexandria on the day of the summer solstice.
Daniel Bruno Sanz: Bad Moon, Burnt Qurans, Birthers and Flat Earthers

Eratosthenes of Alexandria used stick shadows to measure its size to within 95 percent accuracy of today's accepted value.
Daniel Bruno Sanz: Bad Moon, Burnt Qurans, Birthers and Flat Earthers

Dan  Eratosthenes lived around 200BC, and provided the most solid empirical proof of the spherical nature of the Earth.

But the idea was popularized three hundred years earlier, by Pythagoras, and it was commonly accepted by the time Eratosthenes showed up.

As with The Cattle Problem, The Method of Mechanical Theorems was written in the form of a letter to Eratosthenes in Alexandria.

Around 230 BC, Eratosthenes calculated fairly accurately the circumference of the earth.

Eratosthenes used rough estimates and round numbers, but depending on the length of the stadion, his result is within a margin of between 2% and 20% of the actual meridional circumference, 40,008 kilometres (24,860 mi).
Think Progress » Inhofe’s Grandchildren Build Igloo To Mock Killer Snow Storm: ‘Al Gore’s New Home’

Eratosthenes knew that in Syene, in Egypt, the Sun was directly overhead at the summer solstice, while he estimated that the angle formed by a shadow cast by the Sun at Alexandria was 1/50th of a circle.
Think Progress » Inhofe’s Grandchildren Build Igloo To Mock Killer Snow Storm: ‘Al Gore’s New Home’
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