Orbits with

For centuries, humankind has sought to find order in the universe.  In the context of Western tought, in any case, beginning with the Egyptians, Persians, ancient Greeks; in the Americas the Mayans and Azteks, Astronomy evolved out of the necessity to discover a reliable predictor of the seasons for the purposes of agriculture.  In most cases, Astronomy takes on a spiritual role in culture as well.  The system of accounting that ancient peoples used to measure the seasons evolved, after a great amount of suffering and turmoil, into the physics of Gallileo and the mechanics of Newton.  And Newton's remarkable system is still used today, so long as the velocities are not close to the speed of light and the mass vs. density ratio of massive objects is not too great.  Linked above is a gravitational simulator upon which several models of celestial motion are explored.