Scholars in ancient Greece and other early civilizations believed that the earth was flat, which is how it appears to the untutored eye. The idea that the earth might be a sphere, freely floating in space, was first advanced in the sixth century B.C. by the Greek philosopher Pythagoras. Aristotle subsequently provided evidence for this notion. The height of the sun, he noted, changed as one traveled north or south. And that could only be so, he pointed out, if one were traveling along a curve that altered one's line of sight. He estimated that the earth's circumference was 400,000 stades (about 40,000 miles). Around 235 B.C., the Greek scholar Eratosthenes, who was head of the royal library in Alexandria, came up with a clever idea for actually calculating the earth's size. He had heard that there was a well in the town of Syene where the sun cast no shadow at noon on the summer solstice. That meant that the sun must be directly overhead at that moment. Alexandria was thought to be located directly north of Syene, and in Alexandria, at noon on the summer solstice, the sun cast a shadow equal to one-fiftieth of a circle (7.2 degrees). The distance between the two cities was thus one-fiftieth of the earth's circumference. Eratosthenes estimated the cities to be 5,000 stades apart-camel caravans traveling 100 stades a day took fifty days to travel from one city to the other-and thus he concluded that the earth's circumference was 250,000 stades.
From The Map Maker's Wife by Robert Whitaker. Copyright 2004 Robert Whitaker. All rights reserved.
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