Precessional Motion of Sommerfeld's Orbit

This animation clearly depicts the precessional motion of elliptical orbital.In Sommerfeld's elliptical orbit, the velocity of electron is not uniform, because of varying electrostatic force at different distances of it's rotation. It is greatest in closest approach to the nucleus, but gradually decreases as the electron moves farther away. So, according to the Einstein's theory of relativity, the relativistic mass of electron also changes correspondingly. As a result, the electron can not rotate in the same path. Each time the semi-major axis gradually shifts, this causes a precessional motion of the elliptical orbit.