Heh, I recall back in 10th grade, writing a simple solar system simulator in BASIC on my Commodore 64.

A trivial little thing, it just assumed planetary orbits were circular and co-planar, and it knew nothing of gravity -- I just took the orbital periods out of a book. But it did show the planets as animated sprites, with some simple representation of apparent size and phase. Just geometry and algebra; I hadn't had physics or calculus yet.

Sure enough, there was Mars doing retrograde loops, and Venus going from a little disc to a big crescent and back again, all roughly where I had remembered them being in the sky (when I ran it backwards).

Nevertheless, it sure made it sink in that if you started with the Copernican model and first principles of geometry, you got what you actually could see happening out in the real night sky.