How to simulate gravity?

Thought it would be fun to simulate the solar system using physics.

But how to implement gravity for the planets ? One way I thought

would be to use addForce(Vector direction) for each planet and in the direction of the other planets, but problem is

how would you calculate "direction" vector. My problem is really that I suck at math !

Hey Baune, this question came up recently…

and a few years ago here…

Thanks nymon !