Copernicus thought about how the Greeks believed that the universe was sun center(heliocentric). After 25 years of study and research, he concluded that the stars and planets revolve around the sun. Although it is some what correct today, back in the early 1500s it did not fully explain why the planets orbited how they did. Also most people would not believe him due to the on going pressure and influence of the church.
Due to his idea of the heliocentric solar system, it explained why the planets may vary in brightness because they are not always the same distance away as Earth.
Since no one wanted to go against the church, people did not approve of Coprenicus' idea of a sun centered solar system. He knew this which explains why he released his ideas close to his death because if the church wanted to kill him, he was gonna die anyways.
"To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge."
To know that we know things and to know that there are things we don't know is knowledge. By not being closed minded and say that all we know is all there is, then that's true knowledge. A song called "What You Need" the singer of this song explains in an interview and that to think all we know is all there is, it very closed minded.