Re: Planetary orbit simulator. Well, there goes productivity.
Wow Johnson, that is just superb.
I used it to make this picture of the apparent geocentric orbits, showing the epicycles of Jupiter. It shows how the movement of the planets appears to us from earth, with the annual retrograde motion causing the loops as earth speeds past the outer planets. Jupiter gets back to its original position after 11.85 years, and by turning on tracing you can see this picture of nearly six years of Jupiter's apparent motion.