The Northern Lights have been making relatively frequent appearances over the Northwest this summer, but the green tinge captured in photographs above Mt. Rainier on the night of July 12 wasn't the aurora.
It was instead what's known as "airglow."
Unlike aurora, airglow covers the entire planet and is there all the time, caused by reactions between solar energy and certain air molecules. It's just not visible in daytime due to sunlight and is hard to spot at night from other light pollution.
But According to the Atmospheric Optics website, airglow fluctuates a bit with the 11-year solar cycle as increased solar activity can enhance it a bit. And solar activity was high last weekend when these photographers were taken.
Darren Neupert was one of three photographers that captured the airglow recently.
"I thought it was the Northern Lights not only because of the green glow but due to its movement across the sky," he said. "I'm still pretty excited about the shot even though it does not show the Northern Lights. I'll take 'airglow.' "
Nitin Kansal was also surprised to capture the green tinge. He was up at Mt. Rainier to capture images of the Milky Way on a crystal clear night.
"After I came home and downloaded images to my monitor, I was surprised to see faint green color over Rainier," Kansal said. "Initially I thought it might be off-white balance. Then I looked carefully and it looked like it was aurora. I couldn't believe that we could see Aurora looking towards south."
Sure enough some friends clued him in to that it was airglow.
I've captured it on a couple of occasions, both at Mt. Rainier, once when it was incredibly intense and the other with just hints of green glow.
Orion Ahrensfeld has spotted it a few times on his treks.
"Both at Mt. Rainier, once when it was incredibly intense and the other with just hints of green glow. Both times aurora activity was supposed to be low and based on the references I looked up I believe that it is airglow rather than aurora," he said.
Airglow is also easily spotted from space, especially from the International Space Station. You can see it as the faint green ring on the outer edge of our atmosphere in this video (which, as an aside, shows off all the planet's lightning as well. Note that this video at times towards the end also shows the aurora, which is the ribbon-like dancing green curtains.)