When you study the solar system in school, you may be assigned to create a 3-D model of the solar system. There are several ways to make a 3-D model of the solar system. If you need an idea for how to begin, simply make a mobile that is portable and lightweight.
Cut a large circle out of cardboard. The circle should be at least the size of a dinner plate. Find the centre of this circle, and mark the spot with a pencil.
Use a compass to draw a series of smaller circles on the cardboard circle you have made. Make one that is about one or two inches away from the centre, with three more circles around this one slightly farther out. Leave a space of about an inch or so and then make four more circles radiating out toward the edges of the cardboard. Each of these circles will represent the orbit of one of the planets in the solar system.
Use an awl or a screwdriver to punch a hole in the centre of your cardboard circle. Now punch a hole at a random point on the line for each of the circles you have drawn, moving in a different position on each line so you will be able to space out the planets in your display.
Cut pieces of yarn. One piece should be about 12-inches long; the others should each be 9-inches long. Tie a knot in each strand of yarn, 6 inches in from one end. Thread the yarn through the holes from the top of the cardboard circle, putting the longest strand in the centre.
Mold spheres to represent the sun and each of the eight planets using modelling clay. It may be difficult to accurately represent the size of the planets, but do your best to make the proportions realistic. To do this, make sure that the sun is the largest circle. Jupiter, Saturn, Neptune and Uranus should be slightly smaller than the sun, with Earth and Mars slightly smaller than them and Mercury and Venus the smallest of all. Check NASA's website to see a diagram showing the planet's sizes and colours. Add a cardboard ring around Saturn to represent its rings.
Attach one strand of yarn from the top disc to each of the planets. To do this, tie a knot in the bottom of the yarn and poke a thumb tack through that knot. Push the tack into the each of the planets and then let them hang down from your 3-D model of the solar system. Position the planets so that the sun hangs from the centre yarn and each of the other planets hangs in order as they radiate out from the sun.
Use the long tail of yarn you left on the top of the solar system to hang it. Tie a loop in this yarn and hang it from a hook in the ceiling, or attach this yarn to something else such as a light fixture or a crossbeam in the ceiling structure.