Around 270 B.C., the Greek astronomer Aristarchus proposed that Earth and the other planets revolved around a stationary Sun.
He was dismissed as a madman, until Copernicus.
Copernicus studied the movements of the planets in the 1,400 years since Ptolemy and found that Ptolemy’s idea of epicycles, secondary orbits within the main orbit, could not be true.
Copernicus put the Sun in the center with Earth and the planets revolving around it.
This made all his measurements of the planets’ movements make sense. The Copernican system explained the changing seasons, the apparent movement of the stars, and why stars appeared and disappeared from the sky.
It also supported the idea of Earth rotating on its axis and concluded that the stars must be much farther away than previously thought.
Copernicus explained the wandering of the planets in the sky by the different lengths of their orbit around the Sun, not Ptolemy’s epicycles.
Earth had shorter orbits than Mars, Jupiter, and Saturn, the only outer planets known at the time.
Every time Earth seemed to pass these planets in their orbits, the planets would appear to be moving backward.
Copernicus had no better instruments than the ancient world had to measure movements in the sky. His observations were still done basically with the naked eye.
When civil wars were ruining the Polish economy, Copernicus worked out a new money system for the Polish government.