There was the notion among the ancients, although not universal, that a clear distinction had to be made between the earthly ( or sub lunar region) and the celestial heavens both in the type of matter and its motion.
These ideas were of great importance in the Arabic
and European worlds of the medieval ages. Speculations about the nature
of celestial matter, or aether, or quintessence were frequent scholarly
activities into the Renaissance.
In 1572 and 1604 two supernova appeared. The Aristotelian philosophers concluded that these were sub lunar events, since the stability of celestial matter did not allow such alterations to occur in the region of the stars. Galileo himself had written in his early career about celestial matter but latter came to regret this as a fruitless waste of his time.
Dialogue Concerning the Two Chief World Systems