The pink sky was a result of a phenomenon known as airglow.

The sky has been a startling shade of pink for the past week, but it’s not just because of an unusually high amount of pollution. In fact, the culprit is something much more natural. Airglow is a phenomenon that occurs when certain molecules in the upper atmosphere are excited by solar radiation. The molecules then emit light in the red and green part of the spectrum, creating an eerie pink glow that can be seen on Earth’s surface.

Airglow occurs at all times, but it is particularly visible at night during summer months when there are fewer clouds to block out the phenomenon. This year has been particularly impressive because airglow is being made even more visible by the smoke from wildfires in North America and Siberia. These fires have been burning for weeks now and have filled the skies with smoke particles which reflect more light than usual, making them stand out against the pink glow of airglow.