My ex-coworker Todd asked me, “What would happen if a star passed through the Solar syatem?”

I took a slug of beer, and replied thoughtfully and wetly: “I imagine all the planets would be scattered.” But I wasn’t so sure, So I figured, what the heck, I’m unemployed. I’ll just write a simulation.

So here you have it. It’s a little Newtonian gravity simulator, using a straight-up Runge-Kutta integrator of the equations of motion. It takes as input text files that describe the bodies in a planetary system, with their masses and initial positions and velocities. You can center the view on a particular body, or on the center of mass of the system. By clicking in the window you can rotate the view. By sliding the thumb you can zoom in and out.

Kepler’s third law P is period, a is semimajor axis (M₁ + M₂) P² = a³