Dialogue on the Two Chief World Systems, 1632

Galileo visited Rome to seek a revocation of the Copernican censure, and he enjoyed at least six visits with Urban VIII. It was already mentioned that as a Cardinal in 1616, Urban VIII had expressed approval of Galileo’s Letter to the Grand Duchess Christina. Yet Urban was adamant that God could have created the universe according to whatever system he wished, even a system that had not yet been discovered, and therefore one must treat Copernicanism hypothetically. Accepting this condition, Galileo privately obtained the pope’s permission to write an even-handed treatise. This is it, the famous Dialogue on the Two Chief Systems of the World: (Figure 1)

On the left side of the frontispiece (Figure 2) , Aristotle and Ptolemy hold an Earth-centered armillary sphere. On the right, Copernicus, dressed in Catholic garb, holds a Sun-centered model of the universe. Just two systems appear in the Dialogue; Galileo nowhere mentioned the Tychonic system favored by the Jesuits.

Exhibit credit: Kerry Magruder, with the assistance of , Marilyn B. Ogilvie, Duane H. D. Roller.