Asked by severia
Which idea did Ptolemy’s model use to explain why the planets appeared to move backward as they moved in their orbits?
The planets spun in epicycles.
The planets rotated on their axes.
The planets revolved around the Sun.
The planets were made of different materials.
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GPT-5 mini
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The planets spun in epicycles.
Ptolemy explained apparent backward (retrograde) motion by having each planet move on a small circle (an epicycle) whose center moved along a larger circle (the deferent) around Earth; when the geometry lined up, the planet would appear to move backward against the stars.
Ptolemy explained apparent backward (retrograde) motion by having each planet move on a small circle (an epicycle) whose center moved along a larger circle (the deferent) around Earth; when the geometry lined up, the planet would appear to move backward against the stars.
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