Supersonic shock waves. Schlieren image showing the shock wave created by a supersonic jet flying in front of the Sun. Schlieren imaging is a method used to visualise density variations in transparent media. Here, it has been used to view the propagating disturbance in air created by an aircraft moving at the speed of sound. The method requires a bright light source and/or speckled background. In this case, the solar disc has been used, a technique called Background-Oriented Schlieren using Celestial Objects (BOSCO).