When building a solar system model, decide if the model is a box model where the foam balls are cut in half and mounted inside a large cardboard box or a hanging model with the sun at the center. Next gather finger paints and Styrofoam balls of various sizes.
The scale of the planets is an important consideration when deciding how large to make the model. An appropriate sized ball for a sun is about basketball size. Use a large foam ball cut in half for a box model and an inexpensive toy ball for a hanging model. Because the Styrofoam balls are white, add the appropriate colors that represent each planet. Consider the order of the planets starting with Mercury which is the closest to the sun and ending with Neptune, the farthest from the sun.
If the model sun is basketball-sized, Jupiter is 4 to 7 inches in diameter and is painted with brown and white stripes and a light red spot representing the largest storm on the planet. Saturn is yellow with brown or red rings and is 3 to 6 inches, while Uranus is green and 4 to 5 inches in diameter. Neptune is blue and measures between 3 and 4 inches in diameter, while Venus is yellow and 2 inches. The Earth is painted blue and embellished with brown and white to represent the continents and clouds and is also 2 inches in diameter. Mars is red and 1.5 inches, while Mercury is orange and 1 inch in diameter.