Eratosthenes of Cyrene (Cyrene, -276 / Alexandria, -194) was a Greek mathematician, astronomer, and geographer known primarily for being the first person to calculate the circumference of Earth, which made using trigonometry by comparing the incidence angles of the noon Sun at the summer solstice at two locations separated by a north-south distance (Alexandria and Syene). His calculation was remarkably accurate. He was also the first to calculate the tilt of the Earth's axis (again with remarkable precision). In addition, he could have estimated the distance from Earth to the Sun and devised an additional calendar day in four calendars, producing the leap year.He created the world's first map, incorporating parallels and meridians based on available geographic knowledge of his time.
