What key convention did Copernicus initially adhere to that later astronomers like Kepler had to resolve?

Answer

Insisting on perfect circular orbits for the planets

Copernicus’s initial model largely insisted on perfect circular orbits for the planets, a convention that introduced mathematical difficulties resolved later by Kepler using ellipses.

What key convention did Copernicus initially adhere to that later astronomers like Kepler had to resolve?
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