I believe we can use Newtonian Physics to make incredibly good predictions about the movement of celestial bodies as long as they are not too fast/massive and there are only two of them (well, we can make predictions for more bodies, but not the general case, right?)
And I think the only number we need in order to make predictions, besides the positions/speeds/masses of the bodies, is $G$ (i.e. Newton's gravitational constant), and all the math we need is what we call calculus.
But we can make even better predictions if we use General Relativity, and some mathematical objects called tensors, and the speed of light $c$, right? Or do we still need $G$ in GR?