lunar orbit.

This is in its main features the system propounded by Copernicus. But
attention must, to state the case fully, be drawn to two points to be
found in his first and sixth books respectively. The first point
relates to the seasons, and it shows a strange ignorance of the laws
of rotating bodies. To use the words of Delambre,[7] in drawing
attention to the strange conception,

he imagined that the earth, revolving round the sun, ought always to
show to it the same face; the contrary phenomena surprised him: to
explain them he invented a third motion, and added it to the two
real motions (rotation and orbital revolution). By this third motion
the earth, he held, made a revolution on itself and on the poles of
the ecliptic once a year.... Copernicus did not know that motion in
a straight line is the natural motion, and that motion in a curve is
the resultant of several movements. He believed, with Aristotle,
that circular motion was the natural one.

Copernicus made this rotation of the earth's axis about the pole of
the ecliptic retrograde (i.e., opposite to the orbital revolution),
and by making it perform more than one complete revolution in a year,
the added part being 1/26000 of the whole, he was able to include the
precession of the equinoxes in his explanation of the seasons. His
explanation of the seasons is given on leaf 10 of his book (the pages
of this book are not all numbered, only alternate pages, or leaves).

In his sixth book he discusses the inclination of the planetary orbits
to the ecliptic. In regard to this the theory of Copernicus is unique;
and it will be best to explain this in the words of Grant in his great