Size Of The Earth |
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We don't actually know exactly the figure that Eratosthenes got because we don't know how big a "stade" was.
The Arabic scholar al-Biruni in about 990AD calculated the Earth's circumference, getting an answer remarkably close to modern value. Previously the circumference was measured by sighting the Sun simultaneously from two different locations. Instead al-Biruni developed a new method using the angle between a plain and mountain top which made it possible for it to be measured by a single person from a single location.