Erathosthenes

Eratosthenes

Eratosthenes was an ancient Greek scholar who was often called the "father of geography". He was born in "276 B.C.E. at a Greek colony in Cyrene, Libya". The only known information about his family was about his father, who was named Aglaus. He was a poor man and it is assumed that Eratosthenes was also born into poverty. However, he was educated at the academics of Athens, and was "appointed to run the Great Library at Alexandria in 240" by "the ruler of Egypt, Ptolemy III". It is said that "Ptolemy III invited Eratosthenes to Alexandria, Egypt for two reasons; to tutor his son and to be the librarian for the great Alexandrian University." He served as "head librarian and scholar" at the Library, and was the first person to use the word "geography". Even as a young man, Eratosthenes was known for his intelligence and intuitiveness.

Eratosthenes is known for two major accomplishments in the field of mathematics: calculating the circumference of the Earth and what is now known as the "Sieve of Eratosthenes". To calculate the circumference of the Earth, Eratosthenes used the "approximate distance between Syene and Alexandria, as measured by camel-powered trade caravans" and the "angle of the shadow in Alexandria on the solstice". He divided the angle of the shadow by 360 (the result was 50) and then multiplied that number by the distance between Syene and Alexandria. "Eratosthenes determined the circumference to be 25,000 miles, just 100 miles over the actual circumference at the equator (24,901 miles)". His other great mathematical achievement, the "Sieve of Eratosthenes" "determines prime numbers up to any given limit". "Eratosthenes figured out that if you were to write down all the natural numbers from 2 to infinity and "sieve out" every second number after two (or multiples of 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". Using this method, he was able to determine all the prime numbers up to a given limit. These were two of his greatest achievements.

Eratosthenes's contributions are still relevant today. Besides his accomplishments in the field of mathematics, Eratosthenes was "also a well known geographer, astronomer and historian". His experiment to calculate the Earth's circumference helped pave the way for future scientists. "A few decades later, the Greek geographer Posidonius… calculated the circumference on his own and obtained 18,000 miles, 7,000 miles too short". This, in turn, enabled Christopher Columbus to use "Posidonius'