If the image we obtain from Cherenkov light is actually the projection of a continuous wave front (Fig. 1) on a vertical plane, orthogonal respect to the direction of propagation of the incident particle, why we just see a ring (Fig. 2), instead of a full circle? Is it because Cherenkov light is produced only during a brief period, between the entrance of the incident particle in the radiator medium and the instant when its velocity drops below the threshold (Fig. 3)?