We're making a very simple mobile for my son's Easter egg competition - sun, moon and oeuf (ahem). Where should I put the moon - ie behind or in front of sun or earth?
If you use a pea sized moon and put it 2 cm away from the egg the sun would need to me 7 metres away and bigger than a football.
But I think you can use 'artistic licence' in this case.
And... since this is an Easter endeavor, complete accuracy would require that the Moon be on the offside from the Sun (the Earth/Oeuf between the Moon and the Sun, since Easter always occurs very near the Full Moon phase... he said pedantically...
Assuming a pea is half a centimetre in diameter (representing the moon's diameter of about 2,000miles (3,200km)) your "sun" (in reality with a diameter of 800,000 miles or 1.2million km) would need to be 2 metres across.
Representing the Earth as an egg, position a marble about 1/2 metre away to represent the Moon. The Sun might present a bit of a problem as it's 109 times larger than the Earth and about 400 times more distant than the Moon.
The Moon was full 2010 March 30 02:28GMT Tuesday and so opposite the Sun.
Orbiting in an anticlockwise direction (as viewed from above) it will return to this position at about midday on April 28.