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Atlas V's Sonic Boom Made Visible By Sundog

Posted by timothy on from the right-time-and-place dept.

Ross-Shire Geek writes "Atlas V lifted off on Feb 11 from Kennedy. As it goes supersonic through a sundog (aka parhelion) you can see (video link) wonderful visible ripples of the shock wave in the sky."

1 of 99 comments (clear)

  1. Cool - but probably not shockwaves by njord · · Score: 5, Interesting

    Those look like regular acoustic waves to me.

    I don't doubt the the rocket can go faster than the speed of sound (which gets lower as you get further from the surface), but those waves distinctly lead the rocket's motion, which means that they are the product of acoustic perturbations moving at the speed of sound in the medium.

    If the rocket were moving faster than the speed of sound in that medium, then we would see the usual 'shock cone', where those waves would appear an a fairly narrow cone around the rocket as it passed though - certainly not before.

    I qualify 'medium' since it is possible that the rocket is moving faster than the speed of sound (in the air) but not faster than the medium that the sundog constitutes. Liquids, for example, have much higher speed-of-sounds and it is (conceptually, not physically) fairly simple for something to be moving faster than the speed of sound in air at sea level but not be anywhere close to the speed of sound in a liquid that it is travelling - and thus producing the regular u-c, u+c acoustic waves.

    However, as I understand them, sundogs are collections of ice crystals and probably don't have a higher speed of sound than the air around them. But anyway, waves preceding the motion of a body in a medium are certainly not shockwaves - if we could visualize the waves any object makes in the air, you would see acoustic waves arising from the object's motion before and after it.

    Still neat-looking, though.