Nice picture and explanation, but probably wrong. I'm with the commenter Steffen here:<p><i>The shot is probably taken from the ground and during a (relatively) slow maneuver where the aircraft pulls hard up, causing the flow of air to become almost perpendicular to the alignment of the wings, which will cause said large pocket of low pressure which rapidly is equalized causing condensation of the water vapor in the air.</i><p>You can see a similar (very) low speed condensation effect here<p><a href="http://www.airliners.net/photo/Air-France/Boeing-777-228-ER/0981791/&sid=306820fc2c6a8a3183a42afae56afb8f" rel="nofollow">http://www.airliners.net/photo/Air-France/Boeing-777-228-ER/...</a><p>here with a fighter jet but also low speed and high angle of attack<p><a href="http://www.airliners.net/photo/USA---Air/McDonnell-Douglas-F-15E/1130381/&sid=306820fc2c6a8a3183a42afae56afb8f" rel="nofollow">http://www.airliners.net/photo/USA---Air/McDonnell-Douglas-F...</a><p>and this is rather extreme example of the same thing<p><a href="http://www.airliners.net/photo/Russia---Air/Sukhoi-Su-30.../1631566/" rel="nofollow">http://www.airliners.net/photo/Russia---Air/Sukhoi-Su-30.../...</a><p>and here is a similar rainbow effect, but behind an A340 which surely isn't supersonic.<p><a href="http://www.airliners.net/photo/Virgin-Atlantic-Airways/Airbus-A340-642/1088680/&sid=306820fc2c6a8a3183a42afae56afb8f" rel="nofollow">http://www.airliners.net/photo/Virgin-Atlantic-Airways/Airbu...</a><p>Another factor which makes super sonic flight unlikely is that the photographer had to wait for the moment when the sun is behind the aircraft which would be very difficult to do if it was flying that fast.<p>edit: oh and apparently it is called
<a href="http://en.wikipedia.org/wiki/Prandtl–Glauert_singularity" rel="nofollow">http://en.wikipedia.org/wiki/Prandtl–Glauert_singularity</a>