Who was Eratosthenes?

Eratosthenes was a Greek mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandria. He invented the discipline of geography, including some terminology that is used in the 21st century.

Eratosthenes lived from 276 BC to 194 BC. He is best known for being the first person to calculate the circumference of the Earth. His calculations were remarkably accurate. Additionally, it is held that he accurately calculated the distance from the Earth to the Sun and invented leap year. He created the first map of the world incorporating parallels and meridians, based on geographical knowledge that was available at the time.