All of this results from the same cause--namely, from the earth's motion.

The fact that nothing of this is to be seen in the case of the fixed stars is a proof of their immeasurable distance, which makes even the orbit of yearly motion or its counterpart invisible to us."(1) The fact that the stars show no parallax had been regarded as an important argument against the motion of the earth, and it was still so considered by the opponents of the system of Copernicus.

It had, indeed, been necessary for Aristarchus to explain the fact as due to the extreme distance of the stars; a perfectly correct explanation, but one that implies distances that are altogether inconceivable.

It remained for nineteenth-century astronomers to show, with the aid of instruments of greater precision, that certain of the stars have a parallax.

But long before this demonstration had been brought forward, the system of Copernicus had been accepted as a part of common knowledge.
While Copernicus postulated a cosmical scheme that was correct as to its main features, he did not altogether break away from certain defects of the Ptolemaic hypothesis.