This reminds me of a pre-PPC app for Mac I used to LOVE. It was simpler and (if I remember correctly) had a friendlier GUI, but the current Solar System Sim by Dean Dauger is amazing for its completeness. It even has 3-D views, like another Dauger app, Atom in a Box! I found it entertaining and educational. I think Dean could improve the interface a little, by providing us with some onscreen control panels with buttons and sliders with interesting defaults. Nevertheless, if you put even a little time into this, you'll be rewarded with a greater appreciation for the universe we live in and the physics that runs it. The example universes are great. A rich little app... Encourage the author to make it more usable by high-school age kids. (Paying the shareware fee might help!) Dean, if you're reading, get PayPal! It's so much easier than sending you a check! And keep writing great stuff for the Mac. I really appreciate it!
---Shooshie