Eratosthenes

Eratosthenes Teaching in Alexandria (Bernardo Strozzi, Montreal)

Eratosthenes measure of Earth circumference

Mappa di Eratostene

Sieve of Eratosthenes animation

Eratosthenes (c. 276 BC – c. 195/194 BC) was an ancient Greek mathematician, geographer, poet, astronomer, and music theorist who is best known for being the first person to calculate the circumference of the Earth. His work laid the foundations for the field of geography and significantly contributed to the advancement of astronomy in the ancient world.

Life

Eratosthenes was born in Cyrene, an ancient Greek city in present-day Libya. He was educated in Alexandria, which was at the time a major center of learning in the ancient world. Eratosthenes studied under the philosopher Callimachus, who was a librarian at the Library of Alexandria, one of the largest and most significant libraries of the ancient world.

Contributions to Mathematics and Geography

Eratosthenes is most famous for his calculation of the Earth's circumference. He used the differences in the angle of the sun's rays at two different locations to estimate the Earth's circumference. By observing the sun's rays at Syene (now Aswan, Egypt) and Alexandria, he was able to calculate the Earth's circumference with remarkable accuracy for his time. His estimate was within a few percent of the actual value, which is approximately 40,075 kilometers.

Eratosthenes also created one of the earliest maps of the world, incorporating the information from the expeditions of Alexander the Great and other sources. He introduced the concepts of latitude and longitude, and his work in geography was a significant advancement in understanding the world's geography.

Astronomy

In astronomy, Eratosthenes made several contributions. He is credited with inventing the armillary sphere, which was used to determine the positions of the stars. He also attempted to calculate the distance from the Earth to the Sun and the Moon, and although his methods were not accurate by modern standards, his work was an important step in the development of astronomical science.

Other Works

Eratosthenes was a man of many interests and talents. He wrote on a wide range of topics, including philosophy, poetry, and music theory. However, much of his work has been lost over time, and what remains is known primarily through references by later authors.

Legacy

Eratosthenes' work had a lasting impact on the fields of mathematics, geography, and astronomy. He is often referred to as the "father of geography" for his pioneering work in the field. His method of calculating the Earth's circumference laid the groundwork for future geographers and astronomers, and his contributions to the understanding of the world and the universe continue to be celebrated today.