How the Greeks Knew the Earth was a Sphere


‘As long ago as 340 BC the Greek philosopher Aristotle, in his book On the Heavens,
was able to put forward two good arguments for believing that the earth was a round sphere rather than a Hat plate. First, he realized that eclipses of the moon were caused by the earth coming between the sun and the moon. The earth’s shadow on the moon was always round, which would be true only if the earth was spherical. If the earth had been a flat disk, the shadow would have been elongated and elliptical, unless the eclipse always occurred at a time when the sun was directly under the center of the disk. Second, the Greeks knew from their travels that the North Star appeared lower in the sky when viewed in the south than it did in more northerly regions. (Since the North Star lies over the North Pole, it appears to be directly above an observer at the North Pole, but to someone looking from the equator, it appears to lie just at the horizon. From the difference in the apparent position of the North Star in Egypt and Greece, Aristotle even quoted an estimate that the distance around the earth was 400,000 stadia. It is not known exactly what length a stadium was, but it may have been about 200 yards, which would make Aristotle’s estimate about twice the currently accepted figure. The Greeks even had a third argument that the earth must be round, for why else does one first see the sails of a ship coming over the horizon, and only later see the hull?’

– Hawking. S. (1998) A Brief History of Time New York, United States: Bantam Books p. 2

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One thought on “How the Greeks Knew the Earth was a Sphere

  1. In his Acknowledgements to A Brief History of Time, Hawking wrote ‘Someone told me that each equation I included in the book would halve the sales. I therefore resolved not to have any equations at all. In the end, however, I did put in one equation, Einstein’s famous equation, E=mc^2. I hope that this will not scare off half of my potential readers.’

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