Xplanet is a solar system simulator which calculates accurate positions for the major planets and satellites. It displays multiple bodies, eclipse shadows, and customizable labels and markers.
it is great!!!
Superb tool for planetary rendering (especially Earth). I recommend experimenting with the included config files and startup scripts first to get a handle on Xplanet's myriad options. Afterwards, there are several GUI tools and script collections available from other projects to automate downloading updated imagery and marker files.