Einstein's Heroes by Robyn Arianrhod

Author:Robyn Arianrhod
Language: eng
Format: epub
Publisher: Ligature
Published: 2015-05-22T16:00:00+00:00

Armed with this information, and with the belief that the Earth is a sphere, Eratosthenes was able to calculate the circumference of that sphere in an extremely simple way. Taking the Sun to be at the centre of the cosmos, as his older contemporary Aristarchus believed—although the argument can be reversed to apply to a geocentric picture, such as Archimedes supported, and it also applies to an elliptical orbit—this is the way Eratosthenes conceived of the situation: at noon on the summer solstice, Syene and Alexandria are facing the Sun (which thus appears high overhead), and Alexandria is assumed to be due north of Syene, on a meridian of longitude. Each meridian is a complete circle around the globe, the length of the circle therefore being that of the circumference of the Earth.

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