The orbital elements at a given time of a body in an orbit that is perturbed by the gravitational pulls of other bodies, such as the planets. Osculating elements describe the orbit that the body would follow if those perturbations were to cease. However, the real orbit gradually changes because of perturbations, and so the osculating elements alter. Predictions based on osculating elements are accurate only for times close to the epoch of osculation. The way in which osculating elements change with time is a useful way of demonstrating the effects of perturbations on a body’s orbit.