Rheticus, an enthusiastic supporter of Nicolaus Copernicus and his heliocentric theory, publishes Narratio prima ("A First Account").

Following this publication, the sixty-seven-year-old Copernicus, nearly three decades after discreetly circulating his novel heliocentric theory in manuscript form, finally substantiates his arguments with his publication of De revolutionibus orbium coelestium ("On the Revolutions of the Heavenly Spheres").

Challenging the geocentric cosmology that has been accepted dogmatically since the time of Aristotle, Copernican theory is in fact in direct opposition to Aristotle and to Greco-Egyptian astronomer Ptolemy, who had enunciated the details of the geocentric system in the second century.

Ptolemy developed his system through observance of the celestial phenomena of the daily rotation of the heavens, the annual movement of the Sun through the ecliptic, and the periodic retrograde motion of the planets.

The Ptolemaic system, however, requires a complex, and ultimately arbitrary, combination of cycles upon cycles to account for these motions.

Copernicus proposes in "De revolutionibus" that a rotating Earth revolving with the other planets about a stationary central Sun can account for these same observed phenomena in a simpler way.

Copernicus, however, still follows the ancient Aristotelian doctrines of solid celestial spheres and the perfect circular motion of heavenly bodies, and remains essentially wedded to the entire Aristotelian physics of motion.

He also follows Ptolemy in representing planetary motion by means of complex combinations of cycles, although with significant innovations.

Although Copernicus realizes that his theory implies an enormous increase in the size of the universe, he declines to pronounce it infinite.

An undocumented story has Copernicus receiving a printed copy of his treatise on his deathbed; he dies at seventy on May 24, 1543.