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Another indicator of the current state of the sun.

June 26, 2023: There was no geomagnetic storm on June 22nd. Nevertheless, the sky turned green over rural Colorado. Aaron Watson photographed the dramatic display from the West Elk Mountains:

“I woke up around midnight to crystal clear skies,” says Watson. “I noticed some wispy rays and, at first, I thought maybe it was noctilucent clouds. Upon closer inspection there was an intense green glow rippling across the entire sky.”

Although this looks a lot like aurora borealis, it is something completely different: airglow. Cameras with nighttime exposure settings can pick up the faint emission from anywhere on Earth even when geomagnetic activity is low. All that’s required is a very dark sky.

“Airglow is produced by photochemistry in Earth’s upper atmosphere,” says space scientist Scott Bailey of Virginia Tech. “And it is very interesting photochemistry.”

He explains: There is a layer of air about 95 km above Earth’s…