A Greek measured Earth's circumference in 240 BC using shadows.

Eratosthenes, librarian in Alexandria, knew that in Syene the Sun shone straight down a well on 21 June. In Alexandria, a rod cast a shadow of about 7.2 degrees that day, one fiftieth of a full circle. Distance times 50 gave roughly 250,000 stadia. Depending on the stadion's length, he was only a few percent off the true 40,000 kilometres.

Useful: Two measuring points and some geometry are enough for answers that look like high-tech.

Source: en.wikipedia.org

AegyptenAntikeWissenschaft

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