What was Galileo's single most significant observation for shifting the scientific consensus away from the geocentric view?

Answer

The observation of the phases of Venus

The phases of Venus provided the conclusive empirical refutation of the Ptolemaic cosmos because the geometry of the established Earth-centered model could not account for Venus appearing fully illuminated, a phenomenon perfectly predicted by the Sun-centered model.

What was Galileo's single most significant observation for shifting the scientific consensus away from the geocentric view?

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Galileo's Revolutionary Observation - YouTube

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