De Revolutionibus Orbium Coelestium - Contents

Contents

The book is dedicated to Pope Paul III in a preface that argues that mathematics, not physics, should be the basis for understanding and accepting his new theory.

De revolutionibus is divided into six "books" (sections or parts):

• Book I chapters 1-11 are a general vision of the heliocentric theory, and a summarized exposition of his cosmology. Chapters 11-14 are a basic introduction to the mathematics of trigonometry.
• Book II is mainly theoretical and describes the principles of spherical astronomy and a list of stars, as a basis for the arguments developed in the following books.
• Book III describes the apparent movements of the Sun and related phenomena.
• Book IV is a similar description of the Moon and its orbital movements.
• Books V and VI are the concrete exposition of the new system and explain how to calculate the positions of astronomical objects based on the heliocentric model.

Copernicus argued that the universe comprised eight spheres. The outermost consisted of motionless, fixed stars, with the Sun motionless at the center. The known planets revolved about the Sun, each in its own sphere, in the order: Mercury, Venus, Earth, Mars, Jupiter, Saturn. The Moon, however, revolved in its sphere around the Earth. What appeared to be the daily revolution of the Sun and fixed stars around the Earth was actually the Earth's daily rotation on its own axis.

For philosophical reasons, Copernicus clung to the belief that all the orbits of celestial bodies must be perfect circles and to a belief in the unobserved crystalline spheres. This forced Copernicus to retain the Ptolemaic system's complex system of epicycles, to account for the observed deviations from circularity and to square his calculations with observations.

Despite Copernicus' adherence to these aspects of ancient astronomy, his radical shift from a geocentric to a heliocentric cosmology was a serious blow to Aristotle's science—and helped usher in the Scientific Revolution.