Eratosthenes was a Greek mathematician and scholar born in Cyrene, Libya in around 275 BC. Although not considered the best in any field, he made many important contributions across several areas of science and was nicknamed "Beta" as he often came in second to Archimedes. He is best known for accurately calculating the circumference of the Earth by comparing shadows in wells in Syene and Alexandria.

1. ERATOSTHENES’ BIOGRAPHY
Eratosthenes of Cyrene lived approximately in 275-195 BC. He
was born in Cyrene which is now in Libya in North Africa. He
studied philosophy in Cyrene with some philosophers, scholars
and poets. He then spent some years studying in Athens.
Although a brilliant scholar in so many fields, he was never
considered to be the best in any subject. He was also called
Mr. Beta since he always came second as far as his
contributions to science were concerned, since he was a
contemporary and friend of the great Archimedes. This is why
people called him by the nickname of “Beta,” for the second
letter in the Greek alphabet.
Primarily a mathematician, a very important work of Eratosthenes was
Platonicus which, among other topics, discussed the mathematics which are
the basis of Plato's philosophy. Although this work is now lost, Platonicus
studied the basic definitions of geometry and arithmetic, as well as
covering such topics as music.
Despite being lost to history, we know something of Eratosthenes’ work by
the writings of others. Eutocius and other authors described the way
Eratosthenes solved the problem of duplicating the cube. Eratosthenes
later erected a column at Alexandria with an epigram inscribed on it
relating to his own mechanical solution to the cube problem.
Another area in which Eratosthenes is remembered is his work with prime
numbers. Although his original writings are lost, he is remembered for his
'Sieve of Eratosthenes' which, in modified form, is still an important tool in
number theory research
Eratosthenes is probably best known for the surprisingly accurate
measurement of the circumference of the Earth he made. Once again his
treatise, On the measurement of the Earth, is now lost, however, some
information about these calculations appear in works by other authors. He
made a surprisingly accurate estimate of the earth's circumference. In the
great library in Alexandria he read that a deep vertical well near Syene, in
southern Egypt, was entirely lit up by the sun at noon once a year.
Eratosthenes reasoned that at this time the sun must be directly overhead,

2. with its rays shining directly into the well. In Alexandria, almost north of
Syene, he knew that the sun was not directly overhead at noon on the same
day because a vertical object doesn’t cast a shadow when the light is
directly overhead. quot;Well!quot; he thought to himself, quot;everyone knows the
earth is flat! How then, could there be no shadow in Syene when there is a
definite shadow in Alexandria?quot;
Eratosthenes could now measure the circumference of the earth (sorry
Columbus) by making two assumptions - that the earth is round and that the
sun's rays are essentially parallel.
Eratosthenes hired a friend of his
to walk from Alexandria to Syene
to mark the distance.
His friend found the distance between the two
places to be about 500 miles. With this information
and his knowledge of geometry, Erastothenes
determined the circumference of the earth to be
approximately 25,000 miles. And we all know what
has a circumference? Yes!! He proved that the
earth was round. Erastosthenes had changed the
world forever with his discovery, for this led many
seafaring explorers to set sail in search of new and
exciting trade routes. And we all know what
happened after that.
Eratosthenes’ other contributions to astronomy include measurements of
the distances from the Earth to the moon and Earth to the sun and created
a star map containing 675 stars. He also wrote a poem called “Hermes”
which described the fundamentals of astronomy.

3. Eratosthenes also made major contributions to the science of Geography
and, in about 240 BC, became the third librarian at Alexandria, in the
library in a temple of the Muses called the Mouseion. The library is said to
have contained hundreds of thousands of papyrus and vellum scrolls.
Late in his life, he lost his sight. Filled with despair, that his vitality was
gone, he starved himself to death at the age of 80.
GLOSSARY:
 Despite: A pesar de deep: profundo
 Sieve of Eratosthenes: Criba de … well: pozo
 Accurate: exacto treatise. Tratado
 To cast: proyectar to hire: alquilar, contratar
 Lead, led, led: guiar, dirigir vellum scrolls. pergaminos
 Seafaring: navegante to starve: morir de hambre
COMPREHENSION QUESTIONS ABOUT ERATHOSTENES’
BIOGRAPHY
1. Where was he born?
2. Why was he called BETA?
3. What type of contribution did he do to Mathematics?
4. What did people believe about the Earth?
5. Why exactly did he discover that the solar rays were parallel in
Syene and Alexandria?
6. What did he prove?
7. What contributions did he make to astronomy?
8. You know that in Eratosthenes’ times, education was very different
to what we have today. What areas of knowledge did he study and
research on? Compare it with current university degrees.