Shubanshu Shukla captured Earth shining from space. What is airglow?

A thin, glowing line separating the dark sky from Earth offered Group Captain Shubhanshu Shukla a chance to explain what the breathtaking phenomenon is, along with a stellar view from space.

The Indian astronaut took to social media platform X and shared a video showing Earth's curved horizon, city lights below and a faint band of light along the edge of the planet.

The phenomenon is known as airglow, which is a natural, extremely faint light produced by gases high in Earth's atmosphere.

Shukla is the first Indian to visit the International Space Station (ISS) who flew as the mission pilot of Axiom Mission 4 in June 2025.

As part of that mission, he spent 18 days aboard the station, conducting scientific experiments and sharing glimpses of life in orbit.Watching Earth from space never gets boring. You learn something new every time. Like in this video — Earth never truly goes dark. That thin, glowing band hugging the horizon is airglow: a faint emission of light produced continuously in the upper atmosphere. During the day, solar ultraviolet radiation excites and dissociates atmospheric molecules. As these atoms and molecules return to lower-energy states, they release that stored energy as photons — producing a very faint glow, even on the night side of Earth. And no, this isn’t the aurora. Auroras are driven by energetic charged particles from the Sun interacting with Earth’s magnetic field and upper atmosphere, predominantly at high latitudes. Airglow is a much more global phenomenon, driven largely by solar radiation and atmospheric chemistry, and can occur across the planet. The colours tell us something about what is happening at different altitudes: Green — primarily excited atomic oxygen, with strong emission around ~90–100 km. Red — also associated with excited atomic oxygen, but produced through different transitions at higher altitudes. Orange/yellow — can include emissions from sodium atoms deposited in the upper atmosphere by meteoric ablation, as well as other atmospheric emissions such as hydroxyl. Different atoms and molecules, at different altitudes, releasing energy at very specific wavelengths — almost like a spectroscopic fingerprint wrapped around our planet. From the ground, most of this glow is difficult to see because it is incredibly faint. From orbit, looking across the limb of Earth, it becomes much more apparent: a thin, luminous layer separating the darkness of space from the blue planet below. It is a beautiful reminder that the atmosphere is not just the air we breathe. It is a dynamic, chemically active layer — remarkably thin when viewed against the scale of Earth — that makes life here possible. #shux #space #shubhanshushukla #india #axiom4— Shubhanshu Shukla (@gagan_shux) October 4, 2026WHAT IS AIRGLOW?Airglow is a continuous glow produced by atoms and molecules in the upper atmosphere.

Sunlight, particularly ultraviolet radiation, provides much of the energy that drives the processes behind it.

During the day, solar radiation energises or breaks apart atmospheric molecules. The Aurora Borealis, also known as the Northern Lights, illuminates the sky. (Photo: Reuters)

Later, as atoms and molecules undergo chemical reactions and return to lower-energy states, they can release some of that energy as light.

On the night side, these reactions continue, producing what is often called "nightglow".

The glow is extremely faint, so subtle that it's not normally noticeable with the naked eye. But astronauts looking across Earth's edge from orbit can see it as a delicate, luminous band.

Airglow can appear in several colours. Green is strongly associated with atomic oxygen around 95–100 km above Earth, while sodium can produce yellow-orange light around 85–90 km.

Other atmospheric molecules and reactions can produce red and other wavelengths.HOW ARE AIRGLOW AND AURORAS DIFFERENT?

Airglow and auroras can look similar, but they have different causes.

Auroras are produced when energetic particles associated with the solar wind interact with gases in Earth's upper atmosphere, particularly around the polar regions.

Airglow, however, is a much fainter and more widespread phenomenon associated largely with ordinary solar radiation and chemical processes in the atmosphere.

It's present around Earth all the time, although it is difficult to see from the ground.

From the International Space Station, the viewing angle and dark surroundings make the thin atmospheric glow much easier to spot. An image of airglow captured from space by Nasa. (Photo: Nasa)

Beyond its beauty, airglow is also scientifically useful.

Its changing colours and intensity can provide information about the composition, temperature and movements of Earth's upper atmosphere, a region that plays an important role in the environment surrounding our planet.- Ends