Last Friday (Oct.8), Thomas Pesquet, the French astronaut currently on-board the International Space Station posted a stunning image of the Earth on Twitter, that left many people puzzled.

The image taken during nighttime above continental Europe showed artificial light dotting across the continent. However, it also featured a bluish glowing orb in the background, that looked eerily similar to a nuclear explosion.

Fortunately, it wasn’t a nuclear explosion, but rather Pesquet had captured a rare phenomenon called the “transient luminous event”. A phenomenon when lightning-like electrical particles strike upwards in the atmosphere.

Also called ionospheric lightning or upper-atmosphere lightning, these events occur when various charged particles such as plasma interact with each other in the upper atmosphere. The phenomenon, although similar to normal lightning, occurs far above at altitudes of several kilometers above sea level, during thunderstorms.

Pesquet, writing in the photo caption, explained that just a few decades ago scientists weren’t actually convinced these fascinating lighting existed, even though they were described anecdotally by pilots flying in the upper atmosphere.

The reason scientists dismissed the existence of Ionospheric lightning is that they are extremely hard to photograph from the ground, due to their occurrence in high altitudes and due to cloud cover. Additionally, the phenomenon only lasts for a few milliseconds, unlike normal lightning.

Pesquet has only captured only single form of this phenomenon, called the “blue jet”. There are other forms, named red SPRITES (Stratospheric Perturbations Resulting from Intense Thunderstorm Electrification) that glow red, and red ELVES (Emission of Light and Very Low-Frequency Perturbations due to Electromagnetic Pulse Sources) that are also red, but slightly dimmer.

Credit: Wikimedia Commons.

“The Space Station is extremely well suited for this observatory as it flies over the equator where there are more thunderstorms,” says Pesquet. “This is a very rare occurrence and we have a facility outside Europe’s Columbus laboratory dedicated to observing these flashes of light.”

Cover Image: Thomas Pesquet/ESA/NASA