the earth's spin is formed as an ellipse around the sun. so, i was wondering, it is obvious that the earth is changing its distance from the sun along the ellipse, so that means that it loses or gains potential energy along the ellipse as well, therefor, could it be said that the earth gains or loses kinetic energy along the way? because if it is, the earth is constantly accelerating up and down around the sun. also, assuming the earth accelerates tangentanly, it means that in earth reference there should be a different gravitation in different points on earth! so is it true that the earth changes its velocity?