nearer to the earth than at other times. It would also explain the
retrograde motion of planets when in opposition.

We must here notice that at this stage Copernicus was actually
confronted with the system accepted later by Tycho Brahe, with the
earth fixed. But he now recalled and accepted the views of Pythagoras
and others, according to which the sun is fixed and the earth
revolves; and it must be noted that, geometrically, there is no
difference of any sort between the Egyptian or Tychonic system and
that of Pythagoras as revived by Copernicus, except that on the latter
theory the stars ought to seem to move when the earth changes its
position--a test which failed completely with the rough means of
observation then available. The radical defect of all solar systems
previous to the time of Kepler (1609 A.D.) was the slavish yielding to
Plato's dictum demanding uniform circular motion for the planets, and
the consequent evolution of the epicycle, which was fatal to any
conception of a dynamical theory.

Copernicus could not sever himself from this obnoxious tradition.[5]
It is true that neither the Pythagorean nor the Egypto-Tychonic system
required epicycles for explaining retrograde motion, as the Ptolemaic
theory did. Furthermore, either system could use the excentric of
Hipparchus to explain the irregular motion known as the equation of
the centre. But Copernicus remarked that he could also use an
epicycle for this purpose, or that he could use both an excentric and
an epicycle for each planet, and so bring theory still closer into
accord with observation. And this he proceeded to do.[6] Moreover,
observers had found irregularities in the moon's motion, due, as we
now know, to the disturbing attraction of the sun. To correct for
these irregularities Copernicus introduced epicycle on epicycle in the