Which observation challenged Ptolemy's geocentric model of the universe prior to the Scientific Revolution?

💡 Explanation

Mars' retrograde motion challenged Ptolemy's model because it required complex epicycles to explain the apparent backward movement against background stars. Therefore retrograde motion became problematic, rather than stellar parallax, starlight aberration, or supernovae brightness variations which were not observable without more advanced technology.

• Which risk increases when a Roman aqueduct's settling tank experiences turbulent inflow?
• Which navigational outcome was critically improved by the invention of the marine chronometer?
• Which risk increases when seasonal silt deposition reduces Mesopotamian canal flow capacity?
• Which limitation arose when ancient Andean cultures cultivated maize at increasingly high altitudes?
• Which error arises when a 18th-century navigator uses a sextant without correcting for index error?
• Which outcome occurs when constructing timber-framed buildings without proper bracing connections?