This is the trajectory of a luminous pendulum caught from the bottom. The ellipse traced during each cycle undergoes a precession. As the amplitude increases, the oscillation period tends to increase and the system becomes non-harmonic. Since the amplitude of the major axis of the ellipse is greater than that of the minor axis, the periods of both axes are different, which brings the axes to oscillate out of phase and rotate. Red and blue filters were placed side by side on the lens.