Very Rare Solar Halo and 'Sundogs' Filmed Over Mountain

A rare and mysterious halo was filmed over a snow-capped mountain in Sweden, with the footage shared in a viral social media post.

As posted by user @TheFigen_ on Twitter on October 24, the eerie phenomenon appeared as two circles of bright light, hovering in the sky in front of skiers on top of the mountain. One of the circles was inside the other, and each circle had brighter spots of light at the top-, bottom-, left- and right-most points.

This is what's known as a solar halo, and the bright spots of light are "sundogs," both rarely seen phenomena that are only spotted in cold environments. They are caused by the refraction of sunlight through ice crystals in the air, similarly to how rainbows and fogbows are a result of light refracting and diffusing through water droplets of varying sizes.

Refraction is a result of the change in direction of light waves due to a change in their speed after passing through another medium, such as ice or water.

"This is a halo. Halos form whenever sunlight is reflected and refracted by tiny ice crystals in the atmosphere. The appearance of a halo is dependent on the shape and quality of the ice crystals involved in the reflection and refraction of light," Victor Ongoma, an assistant professor of climate change adaptation at Mohammed VI Polytechnic University in Morocco, told Newsweek.

The ring of light is also known as a 22° halo, due to the fact that the sun is at 22 degrees to the viewer.

"The captured halo is a rare halo. The 22° halo surrounds a low sun, while to its left and right are what are known as sundogs. The upper tangent arc is visible on the top while at the bottom is the sun pillar. This phenomenon, especially the arcs crossing the sun (helic arcs), results from hexagonal columnar crystals lying in the horizontal orientation in the atmosphere. Furthermore, its flat prism has to align horizontally as well."

This can also occur with bright moonlight, which in folklore has been thought to mean that bad weather was on the way, as per the saying "ring around the moon means rain soon".

Sundogs have been spotted throughout history, much to the confusion of ancient people. Aristotle is quoted as saying "two mock suns rose with the sun and followed it all through the day until sunset" in Meteorology III.2, 372a14, while a halo with "three suns" is said to have appeared before the Battle of Mortimer's Cross in Herefordshire, England in 1461 during the War of the Roses.

In China in early 2020, a huge sun halo could be seen stretching all the way around the sky, with sundog spots positioned in all directions.

According to the National Weather Service, another strange phenomenon caused by light passing through ice crystals in the air includes sun pillars, which appear as a shaft of light extending up from the sun at sunrise or sunset—most commonly when cirrus clouds are present.