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

When 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.)

What 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.

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