Built systems to conform to the ideals. Predictions of these systems were often discrepant with observations by many degrees. Nested rotating spheres fail to account for the observed changes in brightness of the planets. Puts the Sun, not the Earth, at the center. The Earth rotates and revolves around the Sun.
Stars are on an outermost celestial sphere.
The complex non-uniform and retrograde motions are now just a consequence of viewing moving planets from a moving Earth. It seems that his reasoning was the large size he found for the sun. Showed geometrically that the Sun was at least 20x further than the Moon. Makes it even more absurd that the Sun should move, if the Earth was too large to move according to Aristotle. We know none of the details of Aristarchus' Heliocentric model.