Slashdot is powered by your submissions, so send in your scoop


Forgot your password?

Atlas V's Sonic Boom Made Visible By Sundog 99

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."
This discussion has been archived. No new comments can be posted.

Atlas V's Sonic Boom Made Visible By Sundog

Comments Filter:
  • Wow (Score:3, Insightful)

    by cntThnkofAname ( 1572875 ) on Sunday February 21, 2010 @06:16AM (#31217316)
    There is something incredibly belittling about trying to comprehend the vastness that vehicles like that help us explore.
    • Re:Wow (Score:5, Informative)

      by stjobe ( 78285 ) on Sunday February 21, 2010 @06:21AM (#31217328) Homepage

      Indeed, and apart from that, the linked video is really, really cool.

      Ripples in the sky FTW.

      • Re:Wow (Score:5, Funny)

        by Hadlock ( 143607 ) on Sunday February 21, 2010 @07:30AM (#31217502) Homepage Journal

        A glitch in the matrix, nothing more.

      • Re:Wow (Score:5, Informative)

        by Anonymous Coward on Sunday February 21, 2010 @08:18AM (#31217632)

        To skip the first ~2minutes and cut to the... ripples: [].

        And for even more karma whoring: "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."

        So I guess the normal compression wave by a sonic boom is not enough to alter the way light goes through it (think flickering air when looking across a heated highway), but these ice crystals do the trick. Right?

        • Re:Wow (Score:5, Insightful)

          by Solandri ( 704621 ) on Sunday February 21, 2010 @03:16PM (#31220916)

          So I guess the normal compression wave by a sonic boom is not enough to alter the way light goes through it (think flickering air when looking across a heated highway), but these ice crystals do the trick. Right?

          No, the compression wave always alters the way light travels through it. It's just that normally there's no light going straight through the wave to you, or if there is it's uniform in color and brightness (i.e. blue sky) so altering the direction of the light slightly doesn't produce a visible change.

          My guess would be that the sundog by its very nature means sunlight is at the proper angle at that location to be reflected back to you. A compression wave at this location alters the angle of sunlight being reflected off ice crystals . So the large variability in brightness as a function of small changes in angle makes the ripples visible. Kinda like if someone were trying to signal you with a mirror. If you're seeing blue sky reflected in the mirror, shaking the mirror still yields blue sky so you don't notice any change. But if you're seeing the sun reflected in the mirror, shaking the mirror makes it alternately reflect sunlight and blue sky, causing a strobing effect which is easily visible.

    • Just a huge area with nothing of human value for lightyears.

  • Lucky miss (Score:5, Funny)

    by MichaelSmith ( 789609 ) on Sunday February 21, 2010 @06:22AM (#31217332) Homepage Journal

    I thought that bird was going to get skewered a few seconds into the launch...

  • by Anonymous Coward
    Dr. Evil's rocket launch was so much better. []
  • In 3D (Score:3, Interesting)

    by ivoras ( 455934 ) <ivoras @ f> on Sunday February 21, 2010 @06:51AM (#31217406) Homepage
    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 :)
    • Re:In 3D (Score:5, Informative)

      by Maddog Batty ( 112434 ) on Sunday February 21, 2010 @06:58AM (#31217426) Homepage

      The shockwave is cone shaped rather than spherical for fast moving objects such as a rocket, I believe.

      Very very cool though.

      • Because of the angle, it's hard to tell whether the shockwave is spherical or cone shaped. A cone looks like a sphere while viewed from underneath like in the video.
      • Re: (Score:3, Informative)

        by smitty777 ( 1612557 )

        The 2D aspect was a result of the shape of the clouds that formed the sundog, not the shape of the sonic wave. Sonic waves are indeed conical.

      • Re: (Score:2, Informative)

        by Anonymous Coward

        A shock is indeed spherical right at Mach 1 (which certainly is not "stationary" LOL). As the Mach number increases further, it becomes a cone. The cone half-angle decreases with Mach number and starts at 90 degrees at Mach 1.

    • Second POV (Score:5, Informative)

      by oneiros27 ( 46144 ) on Sunday February 21, 2010 @11:05AM (#31218500) Homepage

      Closer to the pad, and less shaky: []

      (it has the voiceover from NASA TV, but doesn't have the launch clock visible ... it might've been a camera angle that they didn't use live, as I don't remember seeing this on TV)

      • t might've been a camera angle that they didn't use live, as I don't remember seeing this on TV

        correct, I was watching NASATV too and waiting for a nice supersonic plume, but we only got a modest waver on the broadcast camera.

        One of the recent Shuttle launches had one of those nice condensation clouds around the shockwave.

  • Not a sonic boom (Score:1, Interesting)

    by Anonymous Coward

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

    • Re:Not a sonic boom (Score:5, Informative)

      by GrahamCox ( 741991 ) on Sunday February 21, 2010 @08:49AM (#31217738) Homepage
      A sonic boom looks like a single shock wave

      Not necessarily - different edges on the craft will generate additional shock fronts. There are usually two main ones from nose and tail but also from fin tips and even antennae.
      • by thms ( 1339227 )
        You are mixing up two things here:

        The sonic boom is what you hear when any aircraft going faster than mach 1 passes overhead, not just when it breaks the sound barrier.

        The shock wave (very nice to see here: [] (an F-22?)) only happens at around mach 1 when all the sound waves are on top of each other and don't diverge because the source is moving slower or faster than mach 1.
        • The shockwave is a pressure discontinuity that is always there above Mach 1. When it hits your ears, the discontinuity sounds like a boom.
      • Re:Not a sonic boom (Score:4, Informative)

        by Anonymous Coward on Sunday February 21, 2010 @10:09AM (#31218170)

        Exactly [].

        The higher the speed, the more the shock waves become compressed into a series of cones stacked inside each other [] rather than the spheroids typical at slower speeds. Taken together, the passage of these shock waves through a plane perpendicular to the direction of travel would look a lot like circular ripples.

  • by Jane Q. Public ( 1010737 ) on Sunday February 21, 2010 @07:06AM (#31217442)
    Very appropriate, it seems to me, that a rocket carrying the Solar Dynamics Observatory should make pretty with a sundog.
  • I think the word "parhelion" sounds better than "sundog".
    • Re: (Score:3, Interesting)

      by the3stars ( 1030420 )
      They're bad luck for mariners. I respectfully disagree with you, sundog is a much better name.
    • Re: (Score:1, Funny)

      by Anonymous Coward

      Depends how hungry you are.

    • Re: (Score:3, Funny)

      by ZERO1ZERO ( 948669 )
      Isn't that a type of Matrox Video Card?
    • Agree. Sundog sounds like some sort of a weekend snack at the Wienerschitzel.

    • Isn't that a Mozilla product? Sunbird, Firefox, Thunderbird...

      Any idea what that name is supposed to mean? After looking at the Wikipedia article, it seems to me that it would make about as much sense to call it a Sunhippo or Sunrhino...

  • Holy fuck Batman, that was awesome!
  • by MBaldelli ( 808494 ) on Sunday February 21, 2010 @09:30AM (#31217922) Homepage
    What the Saturn V encountered was an Iridescent Cloud []
  • At 2:00 it looks like there are new wavefronts being generated far below the craft. Reflections from the ground? Can't think of any really good explanation.
  • 1) I don't think those are "shock waves," just ordinary very-low-frequency sound waves. I think shock waves occur when a pile of sound waves are forced to stack up on top of each other and create an actual pressure discontinuity.

    2) I was fascinated to hear the background sounds of someone taking photos with a motorized SLR. That is, film... silver nitrate on polyester film. Is that a pro photojournalist? Do they still use film? Or just someone clinging to a nifty old piece of technology that still does the

    • Because it's bad-ass, just like this was.

    • Re: (Score:3, Informative)

      by jhesse ( 138516 )

      That sounded like the music from the awards ceremony at the end, I thought.

    • 3. That wasn't the imperial march. That was the song they played at the end of A New Hope after the Death Star was destroyed during the award ceremony.
    • Re: (Score:2, Informative)

      by budgenator ( 254554 )

      Film is still used, excellent resolution, expose now process later. it will always beat digital in rapid fire situations.

  • 1:54 is really the sole reason we explore space.

  • I drove over to the Canaveral National Seashore [] for this launch. The position of the sun made it very hazy from where I was. This shot [] is geotagged if you're so inclined to see exactly where it was taken. I didn't see that sonic boom wave and no one I was with made any mention of it either. That's really spectacular.

    FWIW, I really love this photo [] of the launch which was taken by a guy in the same spot where I was. It captures the Atlas V flying past the sun which I thought was perfect given the natur
  • by njord ( 548740 ) on Sunday February 21, 2010 @11:59AM (#31218804)

    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.

    • by Zak3056 ( 69287 )

      At 2:01 you can hear the mission controller (or at least the same voice who was calling the countdown, ignition, etc) in the background saying, "Vehicle is now supersonic."

    • Another video of the launch with clean audio. Rocket isn't supersonic until roughly 2 minutes after launch. []

      It didn't look like a shockwave to me from the start, as the name implies, it would be visible as a very sharp, immediate disturbance, not a bunch of ripples. Actually, would have been really cool if it *had* gone supersonic in that cloud layer.

      • Not quite 2 minutes.

        According to the ground loop audio, rocket goes supersonic at 1:38 in that video; launch is at 0:12. So mach 1 is at T+84 seconds or so. This matches my calculations in another thread, which I did using published Atlas rocket launch profiles.

        The amateur video in the summary shows the phenomenon 75 seconds after launch. So while the rocket isn't yet supersonic, it's close. And that makes sense: in the transsonic region just shy of Mach 1, you get violent and irregular pressure-wave ph

  • You know, after getting up in the wee small hours of the morning, driving miles to find a spot to observe the launch and having paid good cash for a video camera (and PC and editing software), you'd think that the joker that took the video would learn **how to pan with the moving object**!. That's "pan with the object" not wait until the object has left the frame and then jerk the camera up until it's at the bottom. And you know, you can buy cameras these days with image stabilization (or even stabilize i
    • Re: (Score:2, Interesting)

      by Yosho-sama ( 800703 )
      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.
    • by mano.m ( 1587187 )
      Mod parent 'unappreciative', 'glass quarter-empty', and 'nitpicking boss from Hell'.
  • Once upon a time, men would have been sitting on top of that rocket. Men with no fear, who couldn't give a shit about politics. They just wanted the ultimate ride.
    Every politician thinking about cancelling Ares needs to think about that. They wouldn't have cell phones and 3G internet and GPS if it weren't for the brave men and women who are, as Steve Buscemei so perfectly put it (minus the nuke):

    "You know we're sitting on four million pounds of fuel, one nuclear weapon and a thing that has 270,000 m
    • by mano.m ( 1587187 )

      Once upon a time, men would have been sitting on top of that rocket.

      I doubt it. It's only putting a satellite in orbit. Why'd anyone put men on that rocket?

  • My explanation (Score:3, Interesting)

    by Thagg ( 9904 ) <> on Sunday February 21, 2010 @01:24PM (#31219580) Journal

    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!

    • by mano.m ( 1587187 )

      I love Mondays. On a Monday, anything is possible.

      That is a genuinely novel and interesting sig. Is it a quotation from someone, or is it you?

  • by goodmanj ( 234846 ) on Sunday February 21, 2010 @03:20PM (#31220944)

    Some debate here as to whether what we're seeing is a sonic boom, or just loud low-frequency sound waves. Let's do the math...

    Basic question: is the rocket going at Mach 1 or greater when the phenomenon happens?

    In the video, the launch happens at 0:38, and the ripples are seen at 1:53, 75 seconds later.

    Here's a handy document [] showing the launch profile of an Atlas V. It doesn't show velocity vs time, but on page 19 there's an acceleration vs time graph for the Atlas V 401, the specific vehicle [] used in this launch. It shows the average thrust during the first 75 seconds is 1.4 +/- .05 g's (uncertain because I can't read the graph that accurately.)

    Subtract out 1 g for gravity pulling the rocket down, to get a vehicle acceleration of 0.4 +/- 0.05 g, which over 75 seconds will lead to a final velocity of 294 +/- 36 m/s.

    The speed of sound is 330 m/s. So at the time we see the ripples, the rocket is riiiiight about at the speed of sound, maybe a little over, maybe a little under, impossible to tell.

    This transition to supersonic flow is often chaotic and irregular, which would explain the intense but complicated ripples seen. If the rocket was going at mach 2 or 3, we'd see a perfectly shaped set of concentric rings; if it was going at far less than mach 1, we'd see nothing at all.

    • Re: (Score:2, Informative)

      by mano.m ( 1587187 )
      It's at about 11 km above the ground after 75 s. At that height, the speed of sound is 295 m/s (WolframAlpha). So it is a sonic boom.
    • by mano.m ( 1587187 )
      PS. Really impressed at how deeply you looked into this. Respect.

Were there fewer fools, knaves would starve. - Anonymous