Atlas V's Sonic Boom Made Visible By Sundog

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."

Comments

In 3D

[ivoras]

More impressively - the sonic boom "waves" effect is actually a three-D object - imagine if we could see it from multiple POVs, a spherical wave instead of 2D one :)

Not a sonic boom

[Anonymous Coward]

A sonic boom looks like a single shock wave. Those look like ripples. Engine sound maybe?

Re:Wow

[Cryacin]

Is it just me, or does anyone else think this is CGI? My first thought was Photoshop!

I guess real life looks less real to me than special effects these days.

Re:Parhelion

[the3stars]

They're bad luck for mariners. I respectfully disagree with you, sundog is a much better name.

Cool - but probably not shockwaves

[njord]

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.

Re:Worst Camera Work Ever

[Yosho-sama]

Not going into the subject of "if you're going to whine about it, do it yourself" but if he hadn't been stationary, he might have missed recording the shockwave event, or recorded it so seeing it wasn't as impressive as we saw.

My explanation

[Thagg]

I've looked at this a few dozen times. It's truly an amazing effect.

Being in the CGI effects business myself (and actually right in the middle of bidding some interesting atmospheric effects for a movie dogfight) I thought it was fake at first, mostly because I've never seen anything like this before. A spectacular display like this, I would have thought, would have been photographed many times if it was a normal occurrence. Some commenters have said that something similar happened on the Apollo XI launch, I haven't seen film that confirms that.

But no, it's clearly real. Many people saw it, several people filmed it.

What it is, is the shockwave moving through a thin layer of clouds and atmosphere. The shockwave disturbs that layer of clouds in some way (in the case of the sun dog, apparently disturbing the crystals orientation -- shockingly these sun dogs require the hexagonal crystals to be hanging more-or-less flat in the air) There are any number of films of airplanes flying above the speed of sound causing clouds to pop into existence and then disappear as the shockwave passes. Every nuclear bomb sequence has these kind of shock-induced clouds as well.

I suppose that clouds with exactly the characteristics to make this happen for rocket launches are rare, because I've watched film of hundreds of launches and never seen this. It always pays to look up!