Obtain Styrofoam balls in various sizes. For this project -- and for all the following ones -- you should have one Styrofoam ball for each of the following sizes: 2.5, 3, 5, 6.4, 7.6, 10, and 15 cm. Also, have two balls of 3.75 cm. The 15 cm ball is for the sun, the 2.5 cm ball will be for Mercury. The two 3.75 cm balls will be for Venus and Earth, the 3 cm ball will be for Mars, the 10 cm ball will be Jupiter, the 7.6 cm ball with be for Saturn, the 6 cm ball is for Uranus, and the 5 cm ball is for Neptune. Paint the balls as you desire for the planets, and then hot glue a dowel to each planet. Glue the other end of the dowel to a piece of plywood that has been painted black.
Obtain and paint Styrofoam balls to represent the planets. Take a large cardboard box, about the size of a large box of diapers, and paint the inside black. Glue dowels to each planet. Glue the other end of the dowel to the inside of the box. You can decide if you want to place the sun in the middle and show the planets in orbit, or place the sun on one side and show the relative distance from the sun of the other planets.
Obtain and paint Stryofoam balls to represents the planets. You can either take two strips of plywood and nail them together to form an X shape and then use that to hang the planets, or you can simply use a hanger. Regardless, using clear mono-filament thread or fishing line, thread an end onto a needle and push the needle into a planet. Cover it with glue or paint to reinforce it. Repeat the process for each planet and tie the other end of the thread to the hanger or plywood.
Obtain and paint Stryofoam balls to represent the planets. Additionally, get a 12 cm ring of Styrofoam and paint it black. Glue the sun to the Stryofoam ring. Insert dowels into each planet and then into the sun. The planets will now appear to be radiating from the sun. Check to make sure you have the planets in the appropriate order. For example, the Earth should be the third planet from the sun.