F = G (m1*m2)/r2
F is the attractive gravitational force between two bodies.
m1 and m2 represent the masses of the two bodies.
r is the separation between the centers of mass of the two bodies.
G is Newton's gravitational constant, where
G = 6.67x10-11 (N*m2)/kg2 (Newtons)*(meters squared) over (kilograms squared).