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What is airglow? This glowing light is not aurora

Airglow: A photograph showing a mountain and the Milky Way and green sky.
View at EarthSky Community Photos. | Makrem Larnaout in Morneg, Tunisia, captured this image on June 18, 2023. Thank you, Makrem! What a fantastic display!

Airglow is the light of excited atoms high in Earth’s atmosphere. It’s usually too faint for the eye alone to see. But under very dark skies, photographers can capture it. Here’s how NASA’s Earth Observatory describes airglow:

The phenomenon typically occurs when molecules (mostly nitrogen and oxygen) are energized by ultraviolet (UV) radiation from sunlight. To release that energy, atoms in the lower atmosphere bump into each other and lose energy in the collision. But the upper atmosphere is thinner, so atoms are less likely to collide. Instead they release their energy by emitting photons. The result is colorful airglow.

But some collisions can also create airglow. In fact, airglow is more common during solar maximum. That’s because the solar activity heats the upper atmosphere, which causes more collisions. Specifically, it causes more collisions that result in greenish light. Spaceweather.com said:

Although airglow does not require solar activity, there is a strong link to the solar cycle. As long ago as 1935, Lord Rayleigh realized that airglow peaks during years around Solar Maximum. Modern studies (e.g., 2011, 2015 and 2022) have confirmed the effect. Airglow is up to 40% brighter when the sun is most active.

Watch a video on airglow

And here’s another view of airglow from the International Space Station.

Starry night sky and curve of Earth's horizon from space with part of ISS visible.
View larger. | Lightning, airglow, and the Milky Way galaxy lit up the night sky as astronauts passed over Kiribati in the central Pacific. Read more about this image. Image via NASA Earth Observatory.

A photo gallery from our readers

If you have a recent photo of airglow to share, send it to us!

Milky Way with dark trees in foreground.
View at EarthSky Community Photos. | Steve Price in Last Chance Desert, Utah, took this image on April 2, 2022. Steve wrote: “The Northern Hemisphere Milky Way season is on! My state is endowed with many dark-sky viewing locations: The Last Chance Desert is my favorite. There was green airglow now and then during my session, satellites galore, aircraft and several meteors, too. I’m pretty sure I captured at least one.” Thank you, Steve!
Bright streak against a black and white background
View at EarthSky Community Photos. | Dan Bush in Albany, Missouri captured this stunning photograph of a bright meteor on June 2, 2022, and wrote: “I have an amateur astronomer-owned meteor monitoring station at my home in Albany, Missouri. The image shown is an image stack of several frames from one of last night’s bright meteors that showed up on several of my cameras. What appears to be high-thin cirrus clouds to the right in this image is actually airglow and was invisible to the unaided eye at the time. I have captured hundreds of bright meteors over the past decade with my monitoring station. I report my observations to the American Meteor Society.” Thank you, Dan!
Vertical Milky Way with green and orangish glow over ocean.
View at EarthSky Community Photos. | Cecille Kennedy in Cape Kiwanda State Natural Park, Oregon, captured this photo of the Milky Way on August 31, 2021. She wrote: “The bright green radiance to the right of the Milky Way, just over Chief Kiawanda Rock, is airglow, also called nightglow. Swedish physicist Anders Angstrom first identified the airglow phenomenon in 1868. It comes in different colors. The green airglow, fainter than zodiacal light, pervades the night sky from equator to pole. It usually appears 10-15 degrees above the horizon of the observer. The green airglow in the photo is not visible to my eyes, but the camera picked it up to my delight.” Thank you, Cecille!

Bottom line: Airglow is a light that occurs high in Earth’s atmosphere. It’s usually too dim to see with the eye, but photographers can capture glorious photographs of it.

The post What is airglow? This glowing light is not aurora first appeared on EarthSky.

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