Fuck Yeah Fluid Dynamics

Watch closely in this high-speed video of a bomb exploding and you will see the spherical blast wave moving outward as a visual distortion. The increase in temperature caused by the leading shockwave changes the index of refraction of the air, bending the light and distorting our view of the background. The mechanism is similar to schlieren photography, which has been used for more than a century to capture images of compressible flows.