Ok, this is one of the coolest toys I’ve played with in a while (or maybe I’m just a science geek). Piotr Kaczmarek has modeled the solar system using both Copernican (sun-centered) and Tychonian (earth-centered) physics. You can set the particular date you want to view, the speed that time goes by, view the zodiac, and even the phases of the moon. If you turn on the planet tracing in the Tychonian model you can see what odd orbits it requires. (via)