To better understand the functioning of a thing, nothing beats simulation.
SimSolar is a program designed to simulate the solar system. It is especially designed for primary schools because of its simple explanations that make it easy to understand the solar system. It shows all the elements of the solar system that move and besides that, it is possible to select a specific date to view eclipses and planetary alignments. It has lots of other features and the easiest way to find out them is to download it.