NASA's Brilliant Photo of Earth's Airglow Helps to Understand Space Weather
The sky is never truly dark.
The Earth doesn’t need the right Snapchat filter to get a healthy glow in photographs.
Take the example of this beauty which NASA released on Tuesday featuring a beautiful starlit sky behind Earth, taken by an astronaut aboard the International Space Station (ISS) in orbit about 250 miles above Australia. In the image, which hardly depicts a “pale blue dot”, the Earth is instead depicted emitting a brilliant, bright yellow-orange glow. The photo was taken on October 7, and showcases a phenomena in Earth’s upper atmosphere past the ozone layer: airglow.
Scientists Like Pretty Colors Too
Our understanding of airglow is thanks to the Swedish physicist Anders Ångström, who was the first to realize that the sky never quite reaches complete darkness. Originally fascinated by the temporary beauty of the Northern Lights, he identified the source of this sky’s perpetual glow as airglow in 1868.
Earth’s atmosphere is primarily composed of nitrogen and oxygen, along with other trace elements. Exposed to sunlight, ultraviolet radiation excites these particles. To shed the extra energy, the molecules release photons, or light particles, which together, create a dim, colorful glow in the Earth’s upper atmosphere, called the ionosphere.
Airglow isn’t only orange, like in the ISS photo. Scientists have also observed green, red, and purple as well. Closer to Earth, particles in the lower atmosphere are more closely packed together, increasing the chance that the energized particles simply collide with one another to release their energy, instead of emitting a photon. But as you move higher, and the chance of collision decreases, particles are more likely to release a colorful photon visible to the human eye. (Although some special collisions release colorful light too.)
But airglow is more than a cloud of pretty colors to observe.
“Each atmospheric gas has its own favored airglow color depending on the gas, altitude region, and excitation process, so you can use airglow to study different layers of the atmosphere,” NASA astrophysicist Doug Rowland explains. “We’re not studying airglow per se, but using it as a diagnostic.”
Welcome to the Ionosphere
The ionosphere where airglow exists lies at the intersection of Earth’s atmosphere and proper space, meaning the region is subject to both Earth weather and space weather — a meteorologist’s nightmare. Understanding how this region works is crucial to those in space and on the ground, since astronauts, satellites, and communication signals (think radio or GPS signals) call the ionosphere home.
To better understand this busy, glowing band of the atmosphere, NASA partnered two missions, the Ionosphereic Connection Explorer (ICON) and Global-scale Observations of the Limb and Disk (GOLD) to provide scientists with close-up and landscape images to build a comprehensive look at the region.
“For years, we’ve studied Earth’s upper atmosphere in detail from the ground and low-Earth orbit,” Richard Eastes, principal investigator of GOLD, said in a statement last January. “By backing out to geostationary, we can put things in a global context. You can see half the Earth from out there.”
So glow up, Earth. NASA is preparing to launch the most detailed photoshoot of your life.