What is precessional motion of the orbit?

Explanation

According to Sommerfeld's relativistic correction of atomic model, an electron revolves in an elliptical orbit around the nucleus, which is located at the focus of the ellipse. This results in a continual charge in the mass and velocity of the electron. the mass of the moving electron increases with its velocity. the velocity of this electron is maximum when closest to the focus of the ellipse (perihelion) and minimum when farthest from the focus (aphelion).
Because of its increased mass at the perihelion, the electron experiences a stronger force of attraction from the nucleus. this compels the electron to deviate from its original orbit to a new and identical orbit, which lie in the sama plane. the perihelion moves each time the electron completes a revolution. thus the entire electron-orbit moves about an axis passing through the nucleus. this phenomenon is known as sommerfeld's precession or precessional motion of the orbit.