Jeong Chang-hoon: Galileo's Dialogue on the Two Chief Systems

Galileo is famous for muttering, "And yet, the Earth moves," as he turned to leave the court while on trial for advocating the heliocentric theory. In his work *Dialogues on the Two Chief Systems of the World*, which clearly demonstrates Galileo's unwavering conviction in the heliocentric theory, he introduces the arguments for the heliocentric and geocentric theories through a four-day dialogue involving three characters. These three figures are Salviati, Simplicius, and Sagredo; Salviati can be regarded as Galileo himself, who advocated for the heliocentric theory, while Simplicius represents the Aristotelian school that advocated for the geocentric theory. Finally, Sagredo acts as the mediator of the dialogue, but in reality, he stands on the side supporting the heliocentric theory. The "two chief systems" in the title refer to the heliocentric and geocentric theories; however, the book's content explains the importance of logical thinking and the proper attitude toward those with differing opinions rather than requiring mathematical calculations, making it easily understandable even for ordinary people without specialized astronomical knowledge. Salviati, Galileo's alter ego, presented concrete evidence during their four-day dialogue—on the first day that the matter of the Earth and the matter of the heavens are not different, on the second day regarding the Earth's rotation, and on the third day regarding the Earth's revolution—and concluded his explanation of the heliocentric theory on the final fourth day with arguments regarding tides. Galileo did not stop there but went further, stating, “God has permitted us to debate the system of the universe, but He has forbidden us from discovering His works. Therefore, we must strive to uncover the system of the universe within the boundaries established and permitted by God.”

Korean title: 갈릴레이 두 우주 체계에 대한 대화

Korean author: 정창훈

Korean publisher: 주니어김영사

ISBN-13: 9788934994404