a change that will not revert on any periodic basis. See also Formation and evolution of the Solar System Frozen orbit Molniya orbit Nereid one of the outer moons of Neptune with a high orbital eccentricity of ~0.75 and is frequently perturbed Osculating orbit Orbit modeling Orbital resonance Proper orbital elements Stability of the Solar System References Bibliography Footnotes Further reading P.E. El'Yasberg: Introduction to the Theory of Flight of Artificial Earth Satellites External links Solex (by Aldo Vitagliano) predictions for the position/orbit/close approaches of Mars Gravitation Sir George Biddell Airy's 1884 book on gravitational motion and perturbations, using little or no math.(at Google books) Dynamical systems Dynamics of the Solar System Celestial mechanics