How did Eratosthenes measure the size of the Earth?by asking Aristotle who knew everythingby walking about one-quarter of the way around its circumferenceby measuring the times of sunrise in each of the four seasonsby measuring the height of the Sun in the sky on the same day in two cities at different latitudesby determining the parallax of the Moon and finding the size of its orbit
by measuring the height of the Sun in the sky on the same day in two cities at different latitudes
Eratosthenes measured the size of the Earth by measuring the height of the Sun in the sky on the same day in two cities at different latitudes. He knew that at solar noon in Syene (now Aswan, Egypt), the Sun was directly overhead and cast no shadow. He also knew the distance between Syene and Alexandria. He measured the angle of the shadow cast by a vertical pillar in Alexandria at solar noon on the same day that there was no shadow in Syene. By using trigonometry, he determined the angle between the Sun and the vertical pillar in Alexandria, and used this angle, along with the distance between Alexandria and Syene, to calculate the circumference of the Earth. His estimation was remarkably close to the actual size of the Earth.
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