It is a book written by Galileo Galilei comparing the Nicolaus Copernicus, published in 1632 aa his dialogue if the two chief world systems.
As in the Copernican system of the universe the earth and the other planets orbit around the sun and while in the Ptolemaic system all orbited around the earth. Simplicio which is a dedicated follower of Ptolemy and Aristotle then presented his traditional simple views.
Being a geocentric philosopher he opposed the heliocentric which proposed the sun in the center.
