This animation uses an orange cone as the wave source. As the cone moves from left to right it emits wave-fronts that continue to radiate out from their position of origin. The cone moves on and establishes a new point of origin for the next wave-front and so on. In this way the waves bunch together at the front of the cone and spread out behind. The situation illustrated is similar to a jet plane approaching the speed of sound and radiating sound waves. In the case of light waves then the higher frequency at the front yields a bluer light (blue shift), while behind the light source (e.g. a star) the light undergoes a red shift.