What is 'Perturbation'
Definition: In astronomical terms, perturbation is the complex motion observed in a massive body that is subjected to forces other than the gravitational pull by another single, massive body. Other forces can include a third body force, resistance caused by another body, as from an atmosphere, and the off-centre attraction of an oblate body.
Description: Perturbations first began to be studied in order to predict the planetary motions in the sky. The hypothetical motion that the body undergoes under the gravitational pull of just one other body is typically a conic section, and can be described in geometrical terms. This is called a two-body problem.
The difference between the hypothetical and actual motion of the body are perturbations due to the additional gravitational pull of the remaining body or bodies. The number of bodies leading to perturbations can be three, known as three-body problem or ‘n’ number of bodies, called as n-body problem.
General perturbations are seen if the forces are one order of magnitude smaller than the gravitational force of the primary body. Perturbations are noticed in Jupiter and the Sun, where Jupiter is 1/1000 of the weight of the Sun.
In our solar system, many disturbances of a planet caused by another planet are periodic, consisting of small impulses each time a planet passes another on its orbit. The orbits of many other minor bodies such as comets are also perturbed by the gravitational attraction of gas giants.