Aristotle believed that the moon’s motion was a result of natural causes. He believed that the moon was not a celestial body, but was instead a “sublunary” body that was subject to change.
In Aristotle’s view, heavenly bodies are perfect and unchanging. The motion of the planets, which he called “wanderers,” is circular and uniform, meaning it moves at constant speed in a perfect circle. However, Aristotle knew that the movement of the planets did not always appear circular and uniform. He attributed this to some kind of force acting upon them from below — in other words, from Earth. This force would cause them to deviate from their circular path, resulting in an apparent change in direction.
According to Aristotle, the moon’s natural and regular motion is circular, but he also thought that the moon sometimes moved in an irregular way. Aristotle believed that this irregular movement was caused by other celestial bodies pushing on the moon. He referred to this sublunary motion as “epicyclic” or “anomalous.”
In fact, Aristotle’s theory about epicyclic motion led him to think that it was possible for the heavenly bodies to create epicycles within epicycles indefinitely. This idea may seem strange today, but at the time it seemed like a good way of explaining how objects could move without violating any laws of physics or mathematics.