Depending on which stadion measurement he was using, his figure was either just 1% too small or 16% too large. He then concluded the Earth must be about 250,000 stadia around. He hired a survey crew, known as bematists, to measure the distance, which they found to be about 5,000 stadia. With this information, he now just needed to know the exact distance between Syene and Alexandria to get the circumference of the Earth (about 50 times the distance between Syene and Alexandria). Thus, at noon on Summer Soltice he used a rod to measure the angle of the shadow made in Alexandria and found it to be about 7 degrees or about 1/50th of a circle. How? He simply used the knowledge that at noon on the Summer Solstice there was a well in Syene where the sun shown directly down to the bottom, with no shadow. Much more definitively, the 3rd century BC head librarian at the Library of Alexandria, Eratosthenes, built on their ideas and managed to calculate the circumference of the Earth with remarkable accuracy. He also noted that during a lunar eclipse the Earth’s shadow is round. Aristotle (4th century B.C.) agreed and supported the hypothesis with observations such as that the southern constellations rise higher in the sky when a person travels south.
Hardly impressive, as noted in our BrainFood Show podcast, bees also use this fact in their own absurdly fascinating navigation and in communicating directions to other bees.Īs for humans, we took a little longer to realize this, with Pythagoras (6th century B.C.) generally credited with being the first known person to have suggested a spherical Earth, though the idea didn’t exactly catch on at this point. Contrary to popular belief, a decent percentage of the human population has known definitely the Earth was roughly spherical for over two thousand years.
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