The Science Behind the Earth’s Airglow

If you were to look in almost any laboratory research notebook that was used in the first year of a NASA employee’s term of employment, you might read terms like “airglow” and “Rayleigh scattering.” That’s because, like the average citizen, even new NASA employees aren’t always aware that airglow even exists, much less knows about the impact of Rayleigh scattering. As for the notebook, who wouldn’t be taking notes concerning their experience as a first year employee of NASA?

Airglow Defined

Some describe it as the Earth’s own radiance. It is a luminosity given off by the atmosphere of Earth. The glow is due to various factors, like the development of molecular oxygen and the reflection of sunlight off of the Earth’s surface. At about 60 miles away from the surface of the Earth, airglow can be seen in its brightest form.

Rayleigh Scattering

Rayleigh scattering has a lot to do with the type of airglow that can be perceived. For example, airglow is more sunlight dominant during periods of time that include muted Rayleigh scattering in the lower atmosphere. As sunlight hits the Earth’s atmosphere, it “scatters” off of molecules. This produces the effect known as Rayleigh scattering and is the reason that the sky looks blue as people look up at it. The process involves wavelength dependence that results in shortened wavelengths that produce this effect.

Types of Airglow

There are three different types of airglow. In the past, it wasn’t easy to see this phenomenon, but the VIIRS instrument has made it possible. Stationed on the Suomi-NPP satellite, it is able to observe Earth because of light that is both emitted and reflected from the planet. It is so powerful that it can see clouds over the Earth at night based on the luminescence produced by airglow. This level of detail can help scientists develop more information about the atmosphere itself, as well as its relation to the surrounding universe. The different types of airglow can help further the process.

Dayglow: As you might imagine, this type of airglow is heavily reliant on sunlight. Referred to as “sunlight dominant,” this is the type of airglow seen as Rayleigh scattering is muted in the lower atmosphere. It also involves resonance and the fluorescent process.

Twilightglow: This type of airglow does not illuminate the lower atmosphere. In fact, only the upper atmosphere is illuminated.

Nightglow: This type of airglow doesn’t have the same brightness of dayglow. At the same time, it is bright enough to outshine the starlight that is found in the night sky. This particular luminescence occurs because of solar radiation. When this radiation interacts with molecules in the upper atmosphere, the result is nightglow.

Without the VIIRS instrument, the world wouldn’t have the images that it now has of airglow. Whether scientists are adding this information to a scientific notebook or not, it is fascinating to understand how light is created in our atmosphere, to the extent that even the color of the sky itself is affected.