Ptolemy and The Almagest
The Complete History of Science
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Ptolemy and the Armagest
In terms of his working methods, Ptolemy clearly derived much from his predecessor, Hipparchus. The Armagest contains a huge catalogue of the fixed stars, over a thousand in all. In total it gathers data taken over the previous 800 years. But its greatest original achievement is a theory of planetary motion. For example, Saturn, Jupiter, and Mars seem to undergo retrograde motion when the Earth-sun and planet are aligned with the Earth at the centre.
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