Question

Why was copernicus' work controversial?

Answer 1

because people liked to believe that the Earth was at the center of the universe and the ptolemaic model of the universe had been seen as accurate for so long that any other idea was dissaproved

Answer 2

Because it contradicted things that are obvious. Anybody with eyes
in his head could go outside at any time, night or day, and see that
the sun, moon, and stars all go around the Earth.
But Copernicus said they don't.