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SYFY WIRE Bad Astronomy

Dancing Lights Against the Sky

By Phil Plait

When you look up in the sky enough, you'll see some really, really weird things. 

YouTube user QuadeM13 was out riding his bike and noticed a strange light beam flashing and twisting around above a cloud. He stopped and took some video of it, and it's, well, really really weird (warning, some NSFW language is muttered therein):

So what is this thing? An alien beacon? Thor going back to Asgard?

Nope. It's ... ice crystals.

Seriously. What's happening here is a wispy cirrus cloud, made up of ice crystals, is being impinged upon from below by a rising cumulus cloud. If the ice crystals in the cirrus are long and needle-shaped, they'll align themselves with the electric field of the lower cumulus cloud, which is generated by up- and downdrafts inside the cumulus cloud. When the electric field suddenly changes (due to, say, lightning discharges inside the cloud), the ice crystals can snap into a different orientation, reflecting and refracting sunlight in a different direction (note that the plume in the video is the same color as the Sun). They do this as a group, making it look like huge coherent structures are suddenly changing shape.

In the video the flare is pretty bright, and I imagine it would be easy to be freaked out by it. I watch clouds a lot and I’ve never seen this, so I doubt it’s terribly common; you need the right circumstances of the cumulus cloud rising into an icy cirrus layer as well as the right geometry to get the sunlight flashing of the crystals.

Back in 2011, I wrote this very odd phenomenon. I had to do some sleuthing to find out what was going on, but what I didn't know at the time is that they're called “crown flashes.” That would’ve made it a lot easier to find out more!

I found a letter to Nature magazine from 1971 describing the phenomenon, so people have been seeing this for a while. A Web search on “crown flash” turns up lots of interesting pictures and videos, too.

The Internet makes finding weird things like this so much easier. I’ve been able to identify iridescent clouds, pileus clouds, and many other weird atmospheric phenomena with just a few clicks. Like any other tool, the ‘Net can be used for ill or for good. I’m glad that it can help us see—and understand—the amazingness all around us all the time.

Tip o’ the Faraday cage to photographer Jerry Lodriguss.

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