David, Your explanation is just fine. The over and under is as simple as you can get. The graphics would be helped immensely by using an orange and a small coin, exaggerating the sizes to get the feel of it across.
Technically the Moon orbits around the center of the Earth-Moon system, which is not trivial. The gravitational pull on the Moon is 53% from Earth, 47% from the Sun: we are a double-planet system, the only one in the solar system. I believe that a trace of the Moon's path with respect *to the Sun* shows it convex at (almost) all times, with very brief "dips" into concavity, mere inflection points. In view of the Earth's mass of 81 moons, the gravicenter mind you is still under the surface of the Earth, but not so close to the center of the Earth: it moves around constantly. That's not trivial either, for us! Number of eclipses: 5 maximum, 2 solar and 3 lunar. Lunar eclipses are actually rarer than solar eclipses, though: they are just visible over the entire dark face of the earth, while solar eclipses are seen only along a narrow path, so that a person's odds of seeing a lunar eclipse are much higher. Bill Thayer LacusCurtius http://www.ukans.edu/history/index/europe/ancient_rome/E/Roman
