• A graphic demonstrating Ptolemy's concept of the Solar System. A smaller circle is at the center of a larger circle. The smaller circle has an X at its center and a small graphic of Earth just below the X. A third, even smaller circle is in the space between the central circle and the larger one, which encompasses both. The third, smaller circle has a planet inside of it with a dotted line that traces its orbit.

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Wikimedia Commons

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Public Domain

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Smithsonian Terms of Use