Problem of the Planets
The model of the universe as the sun, moon, and a sphere containing the stars explains motion of “millions & millions” of stars. But fails for five points of light, the wanderers: Mercury, Venus, Mars, Jupiter & Saturn.
The main motion is similar to the sun moving westward with the stars, but slightly slower. Relative to the stars, they move eastward along the “Zodiac”.
These are the “anomalies” that ultimately led to a revolution in our understanding of the universe.