Copernicus' On the Revolution of the Heavenly Spheres

I am reading this because of how revolutionary of a book it was.  Parts are surprising: it is dedicated to the Bishop of Padua who was apparently a keen astronomy enthusiast.

Other parts are unexpected.  Many of his arguments for heliocentrism are based on the beauty and simplicity that God's Creation implies.

Latter parts of the book are awash in geometry and use of Ptolemy's observations of the planets, which he uses to calculate the inclination of their orbits to the ecliptic, and these seem pretty sound although a bit hard to enjoy, even with gobs of drawings showing triangles.

It also appears that contrary to what I have previously read, he was not insistent on circular orbits and the Ptolemaic epicycles needed to explain retrograde motion of the planets.

Oh yes "prosthapharesis":

"Of the difference in longitudinal prosthaphaeresis caused by this obliquation, consequently, clearly the maximum is also that which occurs at the greatest elongation near point B."  More reading suggests that 500 dollar word refers to greatest angular displacement from the Sun.

He calculates distance from Earth to Venus as 10,000 Earth diameters or about 80 million miles which is not far from the actual 86.28 million miles.