When acting as a third-body perturbation, the gravitational attraction by the Sun and its planets can be modelled by means of point mass attractions. This requires knowledge on the masses and positions of the bodies, as well as some guidelines on which effects are important. In general, for orbit computations of Earth-orbiting satellites it is sufficient to include the planetary gravity due to Venus, Mars, Jupiter and Saturn; the other planets are either too small, or too far away to have any significant impact on a satellite orbit around the Earth.