I've written a java program to model the solar system, and I need to test its accuracy. What would be some good ways to do that? I've checked for conservation of energy and angular momentum. I'm using the velocity verlet algorithm, which seems to have perfectly conserved both of those.
I wondered if there was a way to check if they're back where they started after one orbital period, but couldn't work out how to program a check. I'd really like a way to measure the effect of changing the timestep, but I don't know what a good measure would be? Is there anything else I could do?