The Ptolemaic system of the universe, with the earth at the center, was accepted since antiquity. Following his observations of the heavenly bodies, Copernicus [masked]) abandoned the geocentric system for a heliocentric model, with the sun at the center.
This remarkable work was one of the greatest intellectual revolutions of all time, and profoundly influenced, among others, Galileo and Newton.
The text can be somewhat technical at times but much can be gained from reading how Copernicus expressed his ideas.
After reading Part 1, read the background on his Letter Against Werner and then the letter itself (1 page each) in which Copernicus responds to a request to critique the work of another astronomer, revealing much about how scientists interacted in the 16th century.
On the Revolutions:
https://www.geo.utexas.edu/courses/302d/Fall_2011/Full%20text%20-%20Nicholas%20Copernicus,%20_De%20Revolutionibus%20(On%20the%20Revolutions),_%201.pdf
Background on Letter Against Werner:
http://copernicus.torun.pl/en/archives/astronomical/2/
Letter Against Werner:
http://copernicus.torun.pl/en/archives/astronomical/2/?view=transkrypcja&lang=en
