Eratosthenes of Cyrene
Eratosthenes of Cyrene (c. 276 –194 BCE) became the head of the Library at Alexandria and was rated the most versatile scholar of his time.
He is best known for his remarkably accurate calculations of the Earth's circumference and the tilt of the Earth's axis. He is also credited with calculating the distance from the Earth to the Sun; inventing both the leap day and the discipline of geography; creating the first map of the world, incorporating parallels of latitude and meridians of longitude, and developing the 'sieve of Eratosthenes,' a method for isolating for prime numbers.
He wrote extensively, but only fragments of his work survived the destruction of the Library of Alexandria.
