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.

 Aristotle's cosmology

 Ptolemy's cosmology

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