Biography
Eratosthenes of Cyrene c. 276 BC[1] – c. 195 BC[2]) was a Greek mathematician, geographer, poet, astronomer, and music theorist.
He was the first person to use the word "geography" in Greek and he invented the discipline of geography as we understand it.[3] He invented a system of latitude and longitude.
He was the first person to calculate the circumference of the earth by using a measuring system using stades, or the length of stadiums during that time period (with remarkable accuracy). He was the first to calculate the tilt of the Earth's axis (also with remarkable accuracy). He may also have accurately calculated the distance from the earth to the sun and invented the leap day.[4] He also created the first map of the world incorporating parallels and meridians within his cartographic depictions based on the available geographical knowledge of the era. In addition, Eratosthenes was the founder of scientific chronology; he endeavoured to fix the dates of the chief literary and political events from the conquest of Troy.
According to an entry[5] in the Suda (a 10th-century reference), his contemporaries nicknamed him beta,
from the second letter of the Greek alphabet, because he supposedly
proved himself to be the second best in the world in almost every field.[6]
Eratosthenes was born in Cyrene (in modern-day Libya). He was the third chief librarian of the Great Library of Alexandria, the center of science and learning in the ancient world, and died in Alexandria, then the capital of Ptolemaic Egypt.
Eratosthenes studied in Alexandria, and claimed to have also studied for some years in Athens. In 236 BC, he was appointed by Ptolemy III Euergetes as librarian of the Alexandrian library, succeeding the second librarian, Apollonius of Rhodes.[7] He made several important contributions to mathematics and science, and was a good friend to Archimedes. Around 255 BC, he invented the armillary sphere. In On the Circular Motions of the Celestial Bodies, Cleomedes credited him with having calculated the Earth's circumference around 240 BC, using knowledge of the angle of elevation of the sun at noon on the summer solstice in Alexandria and on Elephantine Island near Syene (now Aswan, Egypt).
Eratosthenes believed there was good and bad in every nation and criticized Aristotle for arguing that humanity was divided into Greeks and barbarians, and that the Greeks should keep themselves racially pure.[8] By 195 BC, Eratosthenes became blind. He died in 194 BC at the age of 82.
