Describe how Eratosthenes first measured the size of Earth over 2,000 years ago
What will be an ideal response?
Eratosthenes used measurements of the angle of the Sun in the sky at noon on the summer solstice in two places in Egypt. It was directly overhead in Syene and cast no shadows. In Alexandria, however, there was a slight shadow, indicating that the Sun was 7 degrees away from overhead. Eratosthenes concluded that Alexandria lies at a latitude 7 degrees north of Syene. The circumference of Earth is then the distance between Syene and Alexandria divided by the fraction of the circle (7/360 ) that the two cities span.
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