when one of the two bodies has a mass that is much smaller, the influence of this smaller body on the larger one is very small, and can be disregarded. in such a case, the problem can be reformulated as a one-centre problem, where there is a stationary big body in the centre, and a small body orbiting around the big one. this setting is very comon. johannes kepler was the first person to formulate and solve it. for this reason, it is also known as kepler problem.