Your definately loosing floating point accuracy which explains the jittering. Other people have tried to recreate a solar system and run into the same problems due to scale.
Imagine you have spaceship flying around the solar system .. One possible way to resolve the problem is to store all the x,y,z global positions of each object, including the spaceship but positionentity each entity relative to the spaceship as it moves ... so the ship is always at world coords 0,0,0. Not sure if I explained that right but it's a bit like a tilemap in 2d - hopefully you get the jist.
Imagine you have spaceship flying around the solar system .. One possible way to resolve the problem is to store all the x,y,z global positions of each object, including the spaceship but positionentity each entity relative to the spaceship as it moves ... so the ship is always at world coords 0,0,0. Not sure if I explained that right but it's a bit like a tilemap in 2d - hopefully you get the jist.