Two Words That Don’t Mean What You Think They Do

sprites_enhanced_stripWhen you hear “gravity waves” or “sprites”, you’d think you would know what is being discussed. After all, those ripples in space-time that Einstein predicted would emanate from twin, colliding, black holes were recently observed to much fanfare. And who doesn’t love early 8-bit computer animations? So when we were browsing over at SpaceWeather we were shocked to find that we were wrong twice, in one photo (on the right).

In retrospect, the waves we were thinking of are actually “gravitational waves”. Gravity waves are any waves where gravity provides the restoring force — think ocean waves. But did you know that the same thing goes on in the atmosphere, and is often visible in photographs of ionic phenomena like airglow?

(“Airglow”, another new term for us, is light emitted by chemical reactions going on in the atmosphere, and was identified by Swedish physicist Anders Ångström, who is famous for spectroscopy, that funny circle above the A in his name, and being very, very short: on the order of 10-10 m tall.)

frankie-lucena-transient_luminous_events_lucena_1445893976What else can illuminate gravity waves? Sprites! They are basically lightning, but instead of cloud-to-ground or cloud-to-cloud, sprites reach out to space. They may be triggered by cosmic rays, and some of them look like jellyfish. They’re hard to see from earth’s surface, naturally, because they’re on the other side of the clouds; you have to be observing at just the right angle. This doesn’t stop folks from trying.

There’s a lot more going on in the sky than we’d thought! And we’ve learned to new meanings for old words. Not bad for one image.

Headline image and sprite taxonomy: [Frankie Lucena].  See more here.

23 thoughts on “Two Words That Don’t Mean What You Think They Do

    1. Bossanova Man, thats the Bees Knees, the Cats Meow. Like the Abacus and Slide Rule, some of your readers have been around longer than silicon computers and internet trolls. All ribbing aside, good article.

  1. Who knew – NSF could have saved $300M dollars on the LIGO experiment trying to detect gravity waves when they could have used an ordinary camera to photograph them. Stupid scientists – they should be reading HAD and they would have found all the proof they needed.

  2. In geophysics, we call these acoustic gravity waves, so there is no confusion, and no one made to feel stupid. Discovered in 1883, when the Krakatoa Volcano blew up, and vertical seismometers in New York rose a tiny amount about 18 hours later. We set up a small microbarograph array in New Mexico to acquire data quantifying the power of the first Chinese nuclear bombs in the late 60s. Our bandwidth was 1 to 1000 second period (1 to .0001 Hz) Rockets blasting off at Cape Canaveral generate AGW (burning 1,000,000 lbs.of fuel in a minute) arriving at Dallas, Tx six hours later. Our military calls it “Infrasonic phenomenon” and still studies it aggressively. It’s all just studying waves in our shallow atmospheric pond when something big is thrown in, and gravity is the restoring force. Yep, it’s been studied for some time now.

    1. The phenomena you described are simply acoustic compression waves requiring a media to pass through. Gravity waves are an entirely different phenomenon, and not related in any way to the processes you describe.

        1. Actually, the primary energy source keeping acoustic gravity waves stirred up are long period ocean waves lifting the atmosphere. P waves are pressure events moving at the speed of sound, carrying what we hear. S waves are in shear, with motion primarily at right angles to the propagation vector, and much lower than the speed of sound. (As in AGW move primarily up and down while slowly propagating themselves around the Earth.
          5.2 Airglow fluctuations
          Atmospheric gravity waves propagating in the thermosphere are known to produce airglow
          variations associated with the wave-perturbed chemistry. Gravity wave motions have been
          detected in the 6300 A (red-line) nightglow, and also in the far-ultraviolet.(from M. P. Hickey “The Tsunami Threat – Research and Technology”)

          1. These are simple acoustic pressure waves. The emission of photons due to compression of atmospheric gasses is not a “gravity” related phenomenon. As Dan suggested, acceleration of mass creates gravity waves, but the phenomenon you are describing have nothing to due with gravity per se, they are simply the result of acoustic wave propagation in a media.

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