Sometimes You Can See Sound

February 17, 2010 4:32 PM

Sonic Boom in a Sun Dog (SLYT)

"Solar Dynamics Observatory Launch, Feb 11, 2010 -- A sun dog is a prismatic bright spot in the sky caused by sun shining through ice crystals. The Atlas V rocket exceeded the speed of sound in this layer of ice crystals, making the shock wave visible from the ground. The announcer can be heard in the video saying: The vehicle is now supersonic."

posted by bwg (45 comments total)

Ho. Lee. Shit.
posted by brundlefly at 4:38 PM on February 17, 2010 [1 favorite]

After about a minute or so, I was about to close the tab, and then it happened.
posted by 517 at 4:39 PM on February 17, 2010 [1 favorite]

If that was a manned craft, I would expect the pilot to have entered an alternate universe.
posted by Countess Elena at 4:40 PM on February 17, 2010

*cues Farscape music*
posted by brundlefly at 4:41 PM on February 17, 2010 [1 favorite]

Wow, thanks for this!
posted by Heretic at 4:42 PM on February 17, 2010

wow, neat!
posted by vorfeed at 4:42 PM on February 17, 2010

What's really scary is realizing that cheesy SF special effects caught up with real life back in the '90s, circa "Sliders".

It is strange that the ripples appear planar when the boom should be radiating at least roughly spherically. (Aside: one of the annoying things about fake SF CGI effects is they often do 2D stuff when the environment is 3D -- like that stupid shockwave ring tacked onto the Death Star explosions in one of the re-edits. A visble blast wave on a planetary surface is ring-shaped due to the intersection of a spherical front with the ground surface, resulting in debris and stuff being kicked up. It makes no sense in space at all.)
posted by George_Spiggott at 4:44 PM on February 17, 2010

Wow. I'd think this was some sort of video from the future, but in the future I expect they'll have cool stuff like tripods and image stabilization.
posted by eyeballkid at 4:45 PM on February 17, 2010 [8 favorites]

Ah. The post answers my question. If the layer of ice crystals is relatively thin then the effect will appear planar.
posted by George_Spiggott at 4:46 PM on February 17, 2010

Wow. That was awesome.
posted by stefanie at 4:47 PM on February 17, 2010

"Sonic Boom in a Sun Dog" sounds like a Grateful Dead album title.
posted by Greg_Ace at 4:52 PM on February 17, 2010 [4 favorites]

We heard you liked sonic booms in your sun, dawg
posted by grobstein at 4:58 PM on February 17, 2010 [2 favorites]

Oh, and it's nice to find out where the term sundog comes from in Schismatrix.
posted by brundlefly at 5:07 PM on February 17, 2010

Nice. Thanks.
posted by Splunge at 5:15 PM on February 17, 2010

Cool!
posted by jquinby at 5:18 PM on February 17, 2010

Oh, and it's nice to find out where the term sundog comes from in Schismatrix.

Time to re-read. Does the Shaper/Mechanist universe remind you of Iain Banks and the Culture? Two of my favorites.
posted by Splunge at 5:19 PM on February 17, 2010 [3 favorites]

Oh, and it's nice to find out where the term sundog comes from in Schismatrix.

Time to re-read. Does the Shaper/Mechanist universe remind you of Iain Banks and the Culture? Two of my favorites.

Shit, I really liked that book. Wonder if I still have it.
posted by grobstein at 5:32 PM on February 17, 2010

Woah. My jaw dropped. As a documented fan of both sun dogs and sonic booms this has to be the coolest thing I've seen in a long, long time.
posted by zsazsa at 5:35 PM on February 17, 2010

This is awesome.

Way to use very well-protected music in order to ensure that not many get to see it.
posted by mike_bling at 5:52 PM on February 17, 2010

This is awesome and I'm so glad it's not a dog exploding.
posted by Juicy Avenger at 5:57 PM on February 17, 2010 [1 favorite]

Better link to save you two minutes of youtube wankery.
posted by jewzilla at 6:02 PM on February 17, 2010 [2 favorites]

"Honey come here you gotta see this!"
posted by nola at 6:07 PM on February 17, 2010

REMAIN CALM
TRUST IN SCIENCE
posted by BitterOldPunk at 6:23 PM on February 17, 2010

Wow. I'd think this was some sort of video from the future, but in the future I expect they'll have cool stuff like tripods and image stabilization.

Oh Metafilter. Don't ever find a way not to snark.
posted by litleozy at 6:28 PM on February 17, 2010 [1 favorite]

Fake.

Sonic booms look nothing like a canned "pebble hitting pond" video effect turned upside-down. Nor do they fade slowly in, then fade slowly out. Nor do they persist in radiating from a small center long after the aircraft has passed.

And what would possess any photographer to add an obviously fake ripple effect to the last second of the credits?!

Perhaps even the sundog was added after the fact. The entire cloud pattern seems to shift as the colors vanish, appearing like a cross-fade between two separate videos.
posted by billb at 6:37 PM on February 17, 2010

Bad Astronomer says Not Fake

Another photo.
posted by Pogo_Fuzzybutt at 7:05 PM on February 17, 2010

Another video. More lame, not as clear. The crowd reaction was something, however.
posted by Pogo_Fuzzybutt at 7:10 PM on February 17, 2010

This page has a link to a much better movie (MOV format, 10 megs)

OK, I'll quit now.
posted by Pogo_Fuzzybutt at 7:14 PM on February 17, 2010 [1 favorite]

Sun Dog Movin'-Air. Is that your final video?
posted by Babblesort at 7:19 PM on February 17, 2010

This is easily one of the coolest and weirdest videos I've ever seen on the net.
posted by loquacious at 7:22 PM on February 17, 2010

I said "FAKE" because sonic booms don't do that. The ripples are very obviously travelling at huge velocity, far faster than sound.

Well, it's not sonic booms. The only thing that could do it is engine noise: a set of sphere-wave ripples intersecting a thin flat cloud layer. The "expanding bullseye" is not sound, it's a moving intersection point.
posted by billb at 7:49 PM on February 17, 2010 [2 favorites]

Bad Astronomer is wrong ...but I agree, NOT FAKE. I was wrong. But it's not shock waves either.

At this scale, shock waves would crawl fairly slowly, while those ripples are moving at way, way faster than the speed of sound.

Instead, it's gotta be engine noise. While the vehicle is far higher than the flat cloud layer, engine noise coming down from above is intersecting the clouds. The "travelling intersection point" would appear as a set of expanding, fast-moving circles. If we could see the actual sound waves, we'd see them travelling much more slowly than the visible ripples.
posted by billb at 8:04 PM on February 17, 2010

Another cool sundog phenomenon:

Thunderstorm e-fields cause LEAPING SUNDOGS

larger leap
posted by billb at 8:10 PM on February 17, 2010

Brilliant!
posted by sundog at 9:21 PM on February 17, 2010

huh, I saw this on spaceweather.com a week ago, and thought it was super neat, but since it was just a low-quality (quicktime) vid shot by a couple of 13 year old girls, I figured it wasn't FPP worthy. This is a much higher quality video, thanks!
posted by lonefrontranger at 9:53 PM on February 17, 2010

those ripples are moving at way, way faster than the speed of sound.

Dude, the waves appeared at precisely the moment when the craft went super-sonic. Super-sonic means greater than the speed of sound. When this happens it causes a sonic boom. We are seeing a visual of the sonic boom. Notice how there is no boom in the video because the waves have not reached the camera. Any wave that is slow enough for our eyes to see is pretty damn slow.
posted by stbalbach at 10:27 PM on February 17, 2010

stbalbach, sound only goes at ~1000 fps, which at that scale isn't too fast to watch. Billb has a good point.
posted by hattifattener at 10:51 PM on February 17, 2010

This is literally the only thing that has ever taken by breath away. Absolutely the one of the most beautiful things I have ever seen. I feel like crying...

Fuck...
posted by Skygazer at 12:23 AM on February 18, 2010

What we're seeing here is aerodynamics meeting geometry: a just-supersonic rocket creating a very shallow conical or near-flat shockwave that is intersecting a flat layer of ice crystals.

When a body is travelling faster than sound the piled-up sound creates a shock wave, in the form of a cone tailing behind the body, the so-called Mach cone. The more highly supersonic the body is, the more pointed the Mach cone becomes.

According to the archived launch commentary the Atlas V went past Mach 1 at around T+80s. On that video, launch is at 0:37, and the 'ripple' is at about 1:53, or T+76s. So it's at around the moment when the rocket is at Mach 1, as the Mach cone is forming. At that moment the Mach cone is more of a flat sheet spreading out from the nose of the rocket.

There's a very nice explanation here, including a Java applet that lets you see the formation of a Mach cone at different speeds. Set it for M=1 and you'll see this flat shock-wave spreading out accompanying the moving body.

Now, imagine that intersecting a flat surface - here, the layer of ice crystals that is giving rise to that sundog. It won't be spreading out from the rocket at the speed of sound, it's a piled-up flat shockwave that hits it pretty much all at once, which is what we see. If there is any radial spread, that would suggest that the rocket is moving at just over Mach 1, and that what we are seeing is a shallow Mach cone passing through the flat layer.
posted by Major Clanger at 12:36 AM on February 18, 2010 [2 favorites]

ANALOGY: when a supernova shock front lights up an interstellar dust cloud between Earth and the supernova, it creates a visible expanding ring which grows at far faster than the speed of light. The visible motion is not a light wave, it's an expanding "locus of intersection" of an expanding sphere contacting a relatively planar dust cloud.

If we could see the sound waves surrounding the rocket, they'd appear as expanding spheres which grow at almost exactly the speed of the rocket (i.e. fairly slowly.) Watch the vid closely: those circles move much faster than the rocket, especially considering that, from our viewpoint, the cloud layer is significantly tilted. I'm even more convinced it's caused by engine noise made visible, sent downwards from a rocket which is positioned well above the cloud layer.
posted by billb at 1:20 AM on February 18, 2010 [1 favorite]

Your ideas are intriguing to me and I wish to subscribe to your newsletter.
posted by peeedro at 7:38 AM on February 18, 2010

The person who took the original video has put a zoomed in version on YouTube here. You can see the vapour cone forming as the rocket goes through the sound barrier just before the ripples appear in the ice layer.

A stunning sequence, regardless of the precise origins of the ripples!
posted by pharm at 11:49 AM on February 18, 2010

Rush synchronicity! Blast offs, sun dogs, oh my!
posted by turbodog at 3:00 PM on February 18, 2010

Sundog can't stand certain kind of sound.
posted by aubilenon at 9:36 AM on February 19, 2010 [1 favorite]

ArmsControlWonk disects the Sun dog thing.
posted by dirigibleman at 10:25 PM on February 19, 2010 [1 favorite]