Sharon,
one of our colleagues at Blackrock Castle ends her planetarium shows with “what is one difference between a planet and a star? — not sure — well, think of the old favourite ‘Twinkle Twinkle Little Planet’ — what? I said it wrong? — then there’s a difference.”
I have seen these made with star stickers or yellow plasticine stars, all can be effective. The interesting learning around mathematics will come when the children look at the models from different angles and see that the Plough Shape is only visible if you are directly above, or, if you hang these on the ceiling , directly below the model.