[LGM]

I believe that combat occurs everyday or when a unit or fleet is supposed to move. If your movement rate is 10, you move every 3rd day. If you enter an enemies position on the 3rd day, combat occurs immeditaely. If both are still there, combat will occur again at a later day (next movement cycle for either player or the next day).

There are some interesting things that happen if you have zero movement (satellites or starbases). I once put a stack of Satellites over an enemy world while we were still at peace. When war broke out, we had combat there about 30 times a turn, but we were both out of range of each other (his platforms and my satellites). It was fun trying to find the real battles every turn. It was also a bit happiness hit because of no decision in the battle, but I had lots of ships in the system at my planets, so I was not affected.