Not every green light in the sky is the aurora borealis. On Sept. 2nd, Mike Taylor was in the Acadia National Park of Maine when he witnessed an intense display of airglow:
Airglow
© Mike Taylor PhotographyAirglow in Acadia National Park.
"It was the craziest airglow I've ever seen," says Taylor. "I was with 3 other photographers and we all saw this with our naked eyes."

Airglow is not an aurora. It's a chemical reaction involving oxygen in the upper atmosphere driven in part by solar ultraviolet radiation and cosmic rays. Visibility waxes and wanes with conditions such as pressure and temperature in the rarified air more than 90 km above Earth's surface. Gravity waves traveling up from the planet below impress the verdant glow with a dramatic rippling structure.

Dark nights with a new or thin crescent Moon are the best times to catch a glimpse of airglow. Often, the glow is dim and pale to the naked eye, revealing its green color only to the lens of cameras set for Milky Way-length exposures. On rare occasions, such as Sept 2nd in the Acadia National Park, the human eye is more than enough. Browse the airglow photo gallery for more sightings.