Create the planets and the Sun using clay. Consider using foam balls, and covering them with clay, to reduce the amount of clay needed and for easily making perfect balls. If planning on hanging the planets, insert a paper clip or other fastener into the clay, leaving enough of a hook outside of the clay, so that a string can be inserted to hang the planet from.
Create a planet to look like Mercury. This planet is orange and gray and is covered in craters. If creating a planet to scale, use a simple scale designed by the Laboratory for Atmospheric and Space Physics as reference. Mercury would be the size of a marble on this scale. Mercury is the closest planet to the Sun.
Create a planet to look like Venus. It is a brown and yellow, almost amber, color. On the same scale, it would be the size of a walnut. Venus is the second closest planet to the Sun.
Create planet Earth. Replicate the oceans and continents with the clay. Earth would be the size of a golf ball. Earth is the third closest planet to the Sun.
Create planet Mars. Mars appears red. This planet would be the size of an acorn on the scale. Mars is the fourth closest planet to the Sun.
Create planet Jupiter. Jupiter is seen by the white, yellow, brown and red bands of clouds surrounding it. It also has a large Great Red Spot, which is an on-going hurricane and has a radius three times the size of planet Earth. Jupiter is the largest planet and is the size of a basketball on the scale.
Create planet Saturn. Saturn appears to be covered by caramel-covered bands. It also has its notorious three rings surrounding it. Cut three rings from card stock and attach them using wire. Saturn is also a large planet; a soccer ball would represent its size using the scale.
Create planet Uranus. Uranus appears to be blue-green. This planet is approximately the size of a soft ball when scaled.
Create planet Neptune. Neptune is blue and has dark blue storms hovering around it. It is the farthest recognized planet from the Sun and is the size of a small grapefruit, using the scale as reference.
Create something to hang the planets from, if not hanging them from the ceiling. If planets were scaled down even further from the scale referenced, create a large cardboard circle mobile base to hang the planets from. Use the top of a pizza pox and cut out a circle, approximately one foot across. To cut the cardboard, you may need a craft knife or box-cutter. Draw a vertical line straight through the center of the circle and then another one horizontally across the center of the circle, dividing the circle in four equal pieces. The center where the lines cross is where the Sun would be. The first four planets are close to the Sun, then there is a space and the remaining planets orbit at the outer edge. Punch holes into the cardboard, using a nail, so that the planets can be hung from the base.
Place string through the hooks on the planets and attach them to the base, through the holes in the base. Secure each end with knots. Hang the base from the ceiling by making six holes at the outer rim of the circle, spacing them equally apart, ideally at 72 degree intervals. Place strong string or rope through these holes and gather them on the top of the base, creating one handle by knotting them, from which to hang the mobile from.