The Northern Ghost

For years, those gazing up into the night at the northern lights wondered what the white-gray patch around them could be.

Now, scientists have an answer.

According to a new study, the white or gray light that is sometimes visible alongside the aurora borealis is a “structured continuum emission,” meaning a light with a continuous spectrum and a structured pattern.

“You’d see this dynamic green aurora, you’d see some of the red aurora in the background and, all of a sudden, you’d see this structured – almost like a patch – gray-toned or white-toned emission connected to the aurora,” study lead author Emma Spanswick said in a statement.

The researchers explained how the emission of this light is “most certainly a heat source” produced through a phenomenon called “chemiluminescence” – light resulting from a chemical reaction.

It represents a new response of our atmosphere to solar activity, suggesting that northern lights are much more complex than previously thought.

Auroras are the result of charged particles generated by the sun which get trapped in Earth’s magnetic field and then collide with atoms and molecules in the atmosphere, releasing energy and causing auroras’ colors.

Spanswick explained that the white-gray patch became visible thanks to advancements in camera technology. Using high-resolution, broad-band color cameras the researchers were able to study 30 separate events where the white-gray continuum was visible, StudyFinds reported.

Color cameras were used to see the shape and movement of the patches, while an instrument called a meridian imaging spectrograph analyzed the spectrum of light they emitted.

Whereas normal auroras shine brighter in specific colors, these patches glow consistently and more brightly across all colors of light, ensuring that this is a real phenomenon and not just a camera illusion.

Spanswick’s fascination with this white-gray ghost sparked from a newly renewed interest in a long, glowing purple ribbon that can appear near northern lights known as Strong Thermal Emission Velocity Enhancement (STEVE).

The study highlighted the relationship and the differences between the white-gray light, auroras, and STEVE. The latter is caused by the energy release of ions moving at supersonic speed in Earth’s magnetosphere.

Spanswick confirms there are similarities between STEVE and the white-gray patches she and her team studied. The spectrum elevation of the two is very similar.

But, while STEVE is an independent phenomenon that can appear even when auroras are absent, the white light is something nearly embedded into the aurora, that would likely have gone unnoticed by the human eye if it weren’t for advancements in digital photography.