The Physics of a Fighter Jet Rainbow | Hacker News Reader

The Physics of a Fighter Jet Rainbow

scienceblogs.com

Nice picture and explanation, but probably wrong. I'm with the commenter Steffen here:

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.

You can see a similar (very) low speed condensation effect here

http://www.airliners.net/photo/Air-France/Boeing-777-228-ER/...

here with a fighter jet but also low speed and high angle of attack

http://www.airliners.net/photo/USA---Air/McDonnell-Douglas-F...

and this is rather extreme example of the same thing

http://www.airliners.net/photo/Russia---Air/Sukhoi-Su-30.../...

and here is a similar rainbow effect, but behind an A340 which surely isn't supersonic.

http://www.airliners.net/photo/Virgin-Atlantic-Airways/Airbu...

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.

edit: oh and apparently it is called http://en.wikipedia.org/wiki/Prandtl–Glauert_singularity

I don't believe it either. I agree with the condensation idea, not with ice crystals. You can see such rainbows near the Sun when it's right at the edge of a cloud, too. (A normal cumulus cloud, not some high altitude cirrus.)

And it's not the P-G singularity either. That's the bow shock condensation when you go supersonic. This is just a variant of the condensation streak you often see of the wings of a commercial airliner when they go full flaps before landing.

That 4th link is an excellent shot of what certainly seems to be the same effect. Quite beautiful, too. Nice find!

Hmmmm, you raise some interesting points. That said, I agree with Ethan that the rainbow in question is a Fire Rainbow. I had never seen one in real life until just recently, but I have seen several in the sky over Paris this summer, and they have the same distinctive colour distribution. Having had the opportunity to see a few, I can tell you that although it is true that the sun needs to be behind the aircraft, the definition of behind is very loose indeed - typically the fire rainbows that I have seen are about a quarter of the sky away from the sun itself (I'm starting to wonder if it's actually 46° away, having read Ethan's explanation), so there is a large expanse of sky where this effect could be seen.

I agree that this is a low-speed manoeuvre though, and not an example of a transonic cloud - have a look at this photo from RAAF Amberley earlier this year: http://www.defence.gov.au/media/download/2010/Jun/20100607/2... - it has the same cloud structure as the F22 photo.

That it's being viewed through a polarized filter is key. If you were to view this unaided, you wouldn't perceive the colours.

My guess is that this caused by internal reflections in a slew of similarly sized water droplets. Much like a rainbow, except that this is backlit.

ok people ..can someone tell me what is that circular "thing" that surrounds the aircraft as the plane crosses the sound barrier? is that moisture or something? if yes how does it occur? an explanation on this would would really fulfill my curiosity.

Here we go: http://en.wikipedia.org/wiki/Prandtl-Glauert_Singularity

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