I am wondering the following: How do one represent the orbital motion of let’s say a planet around the sun with Fourier components? I am learning about Fourier series and I still find it a bit difficult to grasp the concepts. In this case if I understand correctly there will be a frequency that represents how long it takes for the planet to orbit the sun and return to the original position. Which two dynamical variables would we have here? Position and momentum? I have read about the computation of intensities in this case but I have difficulty to understand what is an intensity in this case(since intensities come up most when talking about light where it is the amplitude squared) therefore I wonder what would represent the amplitude in my case and then the intensities? I am sorry for maybe not the clearest problem definition, but I hope you can try to shine light on it in general that would really help my understanding and take an example.