What were the challenges for the ancients to observe the orbit of the Moon (instead of Mars)?
Wasn't it pretty obvious to a careful astrologer a thousand years ago, that the Moon does not have a circular orbit and does not describe epi-cycles?


The ancient Greek model of the motion of planetary bodies remained unchallenged for almost two millennia, so obviously not.

Hipparchus' model did a fairly good job dealing with the elliptical motion of the Moon; it did even better with the planets. The Moon's motion is tough to model because of perturbations by the Sun, Venus, and Jupiter. Ptolemy discovered what would eventually be called evection, the largest of the perturbations caused by the Sun. There was one problem with Ptolemy's model: It had the Moon swinging in and out by a huge amount. If Ptolemy's model was correct, we would see the Moon changing in diameter by a factor of two over the course of a bit over half an orbit. Copernicus much later came up with a scheme that fixed this problem and still relied on those old concepts of deferents, equants, epicycles, etc.

While Newton pointed the way to describing the Moon's orbit, it wouldn't be until 200 years after Newton's death that a decent (one that matches observations) model of the Moon's orbit was developed.