back to article Did you look up? New Year's Day boom over Pittsburgh was exploding meteor, says NASA

The loud boom heard over the skies of Pittsburgh, Pennsylvania, on New Year’s Day was due to an exploding meteor with the blast energy equivalent to 30 tons of TNT, NASA has confirmed. People in the southwestern parts of the US city reported hearing a thunderous roar and feeling the ground shake and windows rattle just before …

  1. KittenHuffer Silver badge
    Boffin

    Pedant Alert!

    "Sonic booms formed by exploding meteors are quite rare, according to the American Meteor Society."

    Technically there is a 'boom' from an exploding meteor, not a sonic boom!

    A sonic boom can be produced by a meteor prior to it exploding (or hitting the ground) while it is travelling faster than the speed of sound. But at the point when (if) it explodes it will just produce an ordinary everyday boom.

    1. John Robson Silver badge
      Boffin

      Re: Pedant Alert!

      Does the physics of a sonic boom change significantly between ~ Mach 1 and ~Mach 60

      1. Paul Kinsler

        Re: Pedant Alert!

        I can't claim any expertise on sonic booms, but my guess that in a simple model would be there would be some change from mach 1 to 2 or 3, but after than not so much. But in a real atmosphere, with a real object it could be quite complicated.

      2. Tom 7

        Re: Pedant Alert!

        Well yes - at Mach 1 its a sonic boom. At Mach 60 a meteor disintegrating is mostly vaporised and the local air heated up rapidly (think thunder) so you dont actually hear the sonic boom as its drowned out by what can only be described as a big fuck-off explosion.

        1. John Robson Silver badge

          Re: Pedant Alert!

          That's just wimping out of the testing - NASA managed a mach 20 wind tunnel in the seventies (using helium IIRC) for shuttle design purposes, so they probably have a pretty good idea on the behaviour up to at least Mach 20...

      3. erikscott
        Mushroom

        Re: Pedant Alert!

        Wow, it's been a long time! Cold War era, first paying job. I was a sysadmin for some folks doing computational fluid dynamics in the Mach 40 region. The big difference in a nutshell is that you really can't entirely model the atmosphere as a gas anymore. You wind up treating it at least partially as a random cloud of various molecules and (violently ionized) atoms. Molecules are being torn up and are recombining into other things, so it's not a constant-molar process across the vehicle. The Navier-Stokes equations start breaking down under those circumstances. Solutions in our group were mostly from something that my naive eye would classify as a Finite Differences simulation. There was a guy doing Monte Carlo simulations - he produced impressively predictive results (I was told) but it was one of those codes that ran for three or four weeks at a time on a Sun 3/280. This was openly published - if I can remember names I could probably find some citations. Cannot remember Monte Carlo Guy's surname for the life of me...

        Icon because that's some non-trivial energy levels you got there, buddy. :-)

        1. John Robson Silver badge

          Re: Pedant Alert!

          Thanks - I was pretty confident that fluid dynamics breaks down at that sort of speed - which possibly does prevent anything so coherent as a sonic boom.

          I (idly) wonder whether that's a feature of the transition from supersonic to hypersonic... I don't imagine the underlying physics changes much from Mach 20 to Mach 100, although having any projectile survive at those higher speeds might make for a challenging testing regime.

    2. Anonymous Coward
      Anonymous Coward

      Re: Pedant Alert!

      So which one is the earth shattering kaboom?

      :)

  2. cookieMonster Silver badge
    Joke

    Other reason

    It could be that new stealth thingy from Area 51

    1. Phil O'Sophical Silver badge
      Coat

      Re: Other reason

      Not very stealthy, though. Unless this was the diversion for the real thing...

      1. Tom 7

        Re: Other reason

        Its just a space Squirrel to distract them.

        1. werdsmith Silver badge

          Re: Other reason

          It's actually NCC1701 re-entering earth atmosphere after time travelling.

          Oh no! I've just disclosed the sys admin password for a million nerds.

          1. Sixtiesplastictrektableware

            Re: Other reason

            But... wait, wouldn't that be 0-0-0-Destruct-0?

  3. Roger Kynaston

    How many of the people?

    That heard the explosion were watching Don't Look Up?

  4. John Brown (no body) Silver badge

    Why do they alway seem to cross the sky?

    All the video I've seen shows them flying across the sky. Surely there must be some that score a bullseye, straight down? Or is it something about orbital mechanics?

    1. Alan Brown Silver badge

      Re: Why do they alway seem to cross the sky?

      "Surely there must be some that score a bullseye, straight down? "

      The problem is that these are only IN the atmosphere for a few seconds (100 miles max) , vs the ones that slide along it for a few thousand miles - and most of the time they're going to hit water

      1. John Brown (no body) Silver badge

        Re: Why do they alway seem to cross the sky?

        Yeah, that makes sense.

  5. sitta_europea Silver badge

    "... (or 0.002 Little Boys)"

    Please don't do that.

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