I'd keep it pretty visual - pictures painting many words and all that...
Lots of photos
Maybe you could attempt to explain the solar system - the size of it.
You could do some work in the classroom on this and then take them out on the oval and have kids stand in the position of the planets and sun relative to each other. That way they could get a sense inside of how big say Jupiter is and yet how far away it is.
Then maybe some painting - Saturn with its rings, Jupiter with the bands, the moon and its craters
Good luck
|