I would also take them on imaginary journeys through the solar system. This requires no more than a box, or even a closet—and your imagination. Rather than just tell them about the solar system, I would “blast off” with them in our imaginary spaceship and we’d travel to each planet in order. I would describe how long it took to get there, what it looked like from orbit, and what it was like to be on the surface, gravity and all.
