The GIF below shows a weird cloud emitting some spooky, extraterrestrial flashes of light in the middle of the day.
The clouds appears to be twitching and convulsing... maybe even, breathing?
Aliens?? No, of course not.
The flashes result from the interplay of the electrical charges found in the atmosphere, the ice crystals that form in clouds, and the light from the sun.
We first heard about it on Reddit, but Discover Magazine blogger Phil Plait saw it and asked meteorologist Joel Gratz, who provided him with a nifty explanation devoid of UFO theories:
The answer lies in this: ice crystals, especially long needles, tend to become aligned with the ambient electric field.
So what you are seeing is sunlight reflecting off ice crystal faces that are constantly being oriented by the developing electric field just above the [cumulonimbus] top. Then there is a discharge in the cloud, and the field collapses momentarily, and the crystals begin to realign again. Then this just keeps happening over and over.
Ice crystals can both hold electrical charges and refract light. The "discharge" to which Gratz refers could be lightning, or some other electrical discharge that disturbs the electrical field, causing the crystals to move. Because they refract the sunlight, the cycle of discharges and realignments creates a fascinating little light show.
We grabbed the GIF from about 40 seconds into the video below, where you will see the lights flashing.