Setting the Scene...
First we need an imaginary Earth. The Earth is called "The Blue Planet" because about 71% of its surface is covered by water, so I made my earth out of blue cardboard made circular by tracing around a CD - but you can use anything you and your Teacher/Mentor like to represent Earth.
To represent the Moon I used a cordial bottle - it is heavy enough not to be moved too much if hit by an errant Robot, and small enough that it is not too big an obstacle to get around.
Have you heard the old myth that the moon is made of green cheese? That myth goes back a long way. Cecil Adams quotes (click here) "John Heywood's Proverbes (1546): "The moon is made of a greene cheese," greene meaning new, unaged." In honour of that old rumour I used green (lime) cordial - but hey - no need to copy my whimsy, use whatever you and your Teacher/Mentor like!
How far apart you place your imitation Earth and moon will depend on your classroom - in my case I put the "Moon" and "Earth" about 60 cms (about 2 feet) apart because that fitted my room (and hence my comments will match that distance) - but if you want to choose a different distance that is fine.
To find out how we can teach our Robot space probe to leave the Earth and go towards the Moon, we can click here
The Far Side of the Moon - Tutorial - NXT-G - LEGO MindStorms NXT - www.DrGraeme.net