Copernicus's Parallax

To an observer in motion, what is at rest may seem to be moving. This phenomenon is called parallax. And its absence was indeed a real mystery for copernicus. Since the fixed stars are so far from us, the changing angle of is tiny and there is no difference in their observed position. Centuries later, the parallax was actually measured using better instruments than those available at the time,. confirming that copernicus had been right.