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. Indeed, he seems to
have retained as much of this as practicable, in deference to the
prejudice of his time. Thus he records the planetary orbits as
circular, and explains their eccentricities by resorting to the
theory of epicycles, quite after the Ptolemaic method. But now,
of course, a much more simple mechanism sufficed to explain the
planetary motions, since the orbits were correctly referred to
the central sun and not to the earth.

Needless to say, the revolutionary conception of Copernicus did
not meet with immediate acceptance. A number of prominent
astronomers, however, took it up almost at once, among these
being Rhaeticus, who wrote a commentary on the evolutions;
Erasmus Reinhold, the author of the Prutenic tables; Rothmann,
astronomer to the Landgrave of Hesse, and Maestlin, the