Posted BY: Pandora Dewan

Mysterious floating lights have appeared over the city of Jeju City in South Korea, with photos of the cylindrical beams being shared on Reddit.

“They have been here for over an hour,” commented the Redditor in a post that has received more than 18,000 upvotes.

Other users theorized that the glowing ghost lights were the work of aliens, but Alex O’Brien, a meteorologist for KOAA News5 in Colorado Springs, told Newsweek that the illuminations were based on something much more terrestrial.

Light pillars are optical atmospheric phenomena where pillars of light appear to beam up from the ground into the sky,” O’Brien said.

The lights occur when tiny crystals of ice, averaging about 0.02 mm (0.0008 inches), form in the sky and remain suspended in the atmosphere, close to the Earth’s surface

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“The suspended ice crystals are great reflectors, beaming city lights back down to your eyes or camera lens,” O’Brien said. “Usually, these are plate-shaped ice crystals, which form at temperatures of 14 to -40 Fahrenheit.”

In other words, for this phenomenon to happen, the weather needs to be cold. “The ideal conditions for this to occur are on a frigid winter night–often subzero temperatures–with high humidity and little to no wind,” O’Brien said.

“It is not too common to see light pillars because the weather conditions must be just right.”

While these conditions are not unheard of in the U.S., they are much more unusual in temperate regions such as South Korea.

On the night in question, the temperature did not drop below 55F. However, the humidity was fairly high, hovering at around 72 percent, and there was very little wind. These conditions would have likely promoted the formation of the light pillars.

light pillars over Russia
Stock image of light pillars over a city in Russia. They are usually seen on cold nights with high humidity and little to no wind. z1b/Getty

“From personal experience living in Colorado, you may see [light pillars] once or twice a winter,” O’Brien said. “The more frigid nights a region sees, the better chance for light pillars throughout the winter.

Depending on the conditions, light pillars can last for hours. “They will remain visible all night as long as weather conditions remain the same,” O’Brien said.

As the mercury drops further, eager sky-watchers may be able to catch a glimpse of these ghostly lights. “To see light pillars, you need to be out at the coldest part of a frigid and humid night,” O’Brien said. “And you should be near a city so there are lights to be reflected.”