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

"I woke up around midnight to crystal clear skies," says Watson. "I noticed some wispy rays and thought maybe it was noctilucent clouds, but upon closer inspection it was intense green airglow rippling across the entire sky."

The ripples look like auroras, but they are not. Airglow is a completely different #phenomenon. It gets started during the day when #sunlight #ionizes# atoms in #Earth's upper #atmosphere. At night, the atoms recombine, giving off light as they make themselves whole again. The green light Watson saw comes from oxygen atoms recombining 90 to 100 km above Earth's surface.

Although these are not auroras, they might still be linked to solar activity. In the 1930s, Lord Rayleigh realized that airglow peaks during years around Solar Maximum. Modern studies in, e.g., 2011 and 2022, have confirmed the effect. Airglow is brightest when the sun is most active. The reason why is not fully understood, but it probably has to do with the sun's increased output of ionizing ultraviolet radiation. More photoionization during the day produces more recombination at night.

That means now is the time to look for airglow. Solar Cycle 25 is intensifying with Maximum perhaps less than a year away. Get away from city lights, wait for the Moon to set, and point your camera at the midnight sky. It might not be as dark as you think.
https://spaceweather.com/