Eratosthenes
Eratosthenes was a prominent Greek mathematician, astronomer and geographer who lived between 276 BC and 194 BC. He was born in what is now Libya, to parents who were probably Chaldean.
Eratosthenes is famous for many things, including a mapping method that used latitudes and longitudes, and his accurate computation of the circumference of earth. To compute for the circumference of the earth, Eratosthenes used the principles of trigonometry and available data on the altitude of the sun in two specific locations at noontime. He worked on the assumption that because the sun was very far from earth, its rays could be considered parallel.
He then used the sun’s positions from two known, different locations to come up with 252,000 stadia as the size of earth. Roughly, this translates to about 40,000 to 46,000 km; the actual earth circumference is about 40,000 km.
Erathosthenes also introduced a method of finding prime numbers, which to this day bears his name (the “Sieve of Eratosthenes“). He further gave accurate measurements of the distances of the earth from the sun and from the moon. He compiled a star catalog that consisted of 675 stars. He made maps of Egypt and other important centers of civilization. He too was the first to coin the word “geography.” And he invented a device called the armillary sphere. As can be seen, he excelled in many branches of learning, especially in astronomy, arithmetic, geography and even music.
Despite his many achievements, Erathosthenes acquired the rather insulting nickname “Beta.” He was also called “Pentathlos”, which meant a wellrounded and accomplished athlete, but one who never got first place. Erathosthenes did make many important discoveries and contributions to science, but he always came up second to someone else. He never became the foremost authority on any discipline, but always the second, the runnerup, or the beta. It didn’t help that Erathosthenes had a rather eccentric and haughty character, which probably turned off some people.
Eratosthenes became blind in the latter part of his life. This must have proven to be a serious impediment to his scholarly work, discouraging him greatly. A year later, he committed suicide by starving himself to death.

http://Eratosthenes GABRIEL LEVY

http://Eratosthenes GABRIEL LEVY

http://lenz_g15@yahoo.com glena marie moreno