Galileo Galilei's Dialogue Concerning the Two Chief …
Years: 1632 - 1632
Galileo Galilei's Dialogue Concerning the Two Chief World Systems (Dialogo sopra i due massimi sistemi del mondo), published in the Italian language in 1632, compares the Copernican system, in which the Earth and other planets orbit the Sun, with the traditional Ptolemaic system, which has everything in the Universe circling around the Earth.
Published in Florence under a formal license from the Inquisition, and dedicated to Galileo's patron, Ferdinando II de' Medici, Grand Duke of Tuscany, the book is a bestseller.
The bulk of Galileo's arguments may be divided into three classes:
* Rebuttals to the objections raised by traditional philosophers; for example, the thought experiment on the ship.
* Observations that are incompatible with the Ptolemaic model: the phases of Venus, for instance, which simply couldn't happen, or the apparent motions of sunspots, which could only be explained in the Ptolemaic or Tychonic systems as resulting from an implausibly complicated precession of the Sun's axis of rotation.
* Arguments showing that the elegant unified theory of the Heavens that the philosophers held, which was believed to prove that the Earth was stationary, was incorrect; for instance, the mountains of the Moon, the moons of Jupiter, and the very existence of sunspots, none of which was part of the old astronomy (though these are of somewhat doubtful relevance, as none of these phenomena dealt directly with the question of the motion of the earth or sun).
