Great thinkers like Aristotle and Plato may have contributed mightily to philosophy, but their ideas about astronomy were out in space. Most Greeks believed that the Earth was the center of the universe, and that all celestial bodies in the sky rotated around it. They held that the sun, stars and other planets were attached to invisible spheres around our planet. Ptolemy amended the theory by rejecting the notion that the invisible spheres were concrete objects the sun and stars were affixed to. Copernicus proposed the theory of heliocentrism - - the sun was the center of the universe and all the planets orbited around it; still, he couldn't account for planetary movements and he believed they rotated in a perfectly circular pattern. In the decades around 400 B.C., without the aid of the telescope or any of the elaborate equipment used by today's astronomers, Democritus was able to arrive at startlingly accurate conclusions. He proposed that the universe was made up of atoms. And in looking at the night sky, he deduced that our Milky Way is composed of stars that appear to be pinpoints of light because of their distance.
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