Off- course moon orbits?

[Godofpie]

Sometimes when there is a planet orbiting a Sun and I want a moon(s) to orbit the planet e.g. Moon orbiting Earth which is orbiting the Sun, the moon will orbit the Earth for a few minutes, and then will go off-course and begin to orbit the sun and go way ahead of the Earth. I really want to fix this since I wanna make a proper galaxy. Also, the planets have the same problem. If a Star is orbiting a Galaxy center , and a planet is orbiting the star, sometimes, not just the moon will go off-course, and so will the Plantet go off course to orbit the galaxy center.
If anyone knows how to sort this out please post it   

[vh]

You probably have the time step set too high. You can slow it down manually or press 'a' to auto-timestep.

[Unreal2004]

Yep, you have to think of the timestep setting as your accuracy setting.  If you have your timestep set high to make the simulation run faster it will be less accurate, imagine it this way:  If you have a circle and you create a point each tenth of a second while drawing the circle you will have an accurate image of the circle but if you create a point every second while still moving the same speed while drawing you will have a very rough image of a circle, go up to every 5 seconds and it looks even less like a circle, thats how the program figures an orbit in laymans terms, each time you increase your timestep your decreasing the accuracy of your simulation by lowering the points at which all the bodies are measured, eventually you get things flying around randomly since the gaps between points is too large.