I have been trying to map the location of the sun in the sky by using three dimensional vector analysis. I can find the rectangular equations of the elliptical orbit with the sun at one of the focal points, however I don't know the function of the angular acceleration of it's orbit. I know the maximum tangential velocity is 30.287E3m/s at perihelion and the minimum tangential velocity is 29.291E3m/s at aphelion but I don't know if the acceleration is a linear function. I would assume it is not linear, or not constant acceleration. I was wondering if anyone knew the angle as a function of time equation?