shocking

This super cool photo shows transonic airflow around the Blue Angels F-18 with superb clarity. Unlike many similar photos - popular as computer wallpaper - that reveal only condensation in the expansions following the shock waves, here we see the shocks themselves by way of background distortion. This works best when the background has strong light-dark boundaries, as in the case of the white boats against the dark water. The shock wave pattern is complicated over the wings and tail, but note the single shock which terminates a local supersonic-flow region generated by the canopy. Also the white water following the shock wave system is caused (I think) by the fact that moving shock waves drag an airflow behind them that is strong enough in this case to whip the water into froth. Finally, the shocks above and below the aircraft tail have a distinctly “glassy” appearance. To me this is the most fascinating thing about this photo. On those rare occasions when you can see them, shock waves in air look just like streaks in glass. Both are invisible unless revealed by background distortion. If you click on the photo all of this might be easier to see as it makes it bigger on your screen.