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How large did Ptolemy estimate the universe to be?
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Ptolemy
Ptolemy's theory of the solar system.
Ptolemy estimated the size of the universe to be approximately 20,000 times the radius of the Earth.12
In his work Planetary Hypotheses, Ptolemy proposed a nested-spheres cosmology where he assumed there was no empty space between the heavenly bodies. By using the known distance of the Moon as a scale and calculating the distances of the planets based on his geocentric model, he determined that the celestial sphere—which contained the stars—formed the outer limit of his universe at that distance. While this was considered an enormous cosmos at the time, it is significantly smaller than modern scientific estimates.12