List observations of various images and diagrams of the solar system taken from the Web. Use these illustrations and their understanding of orbits to begin a unit-long KWL Chart and start a guided discussion. Go to NASA's Windows to the Universe Solar System Formation web site. Click on the small image of our solar system to get one that fills the screen. Point out the orbits of each of the planets shown on the diagram.
Orbits are paths that describe dynamic phenomena.
It is hard to deduce the shapes of planetary orbits from our moving Earth, but in some cases we can directly observe objects that are orbiting the planets. The following extension activities may be helpful. There are commercial solar system simulators available as shareware. The sizes of the orbits and the orbital periods are correctly proportioned in this package. Ask students if they have observed satellites moving overhead and, if so, to describe to the class what they have seen.