Albertans treated to display of 'light pillars,' which appear on cold, calm nights

When Ryota Suyama woke up at around 4 a.m. Tuesday, it looked like an alien invasion had taken over the town of Canmore.

Columns of light shot into the night sky above residents' rooftops, illuminating a backdrop of snow-covered mountains. 

"It was kind of surreal," Suyama said.

"We've seen, you know, northern lights a couple of times, but we had never seen light pillars before.… It almost felt like it was happening right in front of us, so it was definitely astounding."

Suyama is one of many Alberta residents who witnessed the sight this week, with columns of light being seen from Spruce Grove to Calgary.

Light pillars happen on very cold, clear evenings when tiny ice crystals form in the atmosphere, according to Jeroen Stil, associate professor in the department of physics and astronomy at the University of Calgary. 

On calm evenings, the crystals hang at just the right angle to act as small mirrors reflecting any light beaming up at them from below, such as a street lamp or lighting on a commercial building.

"Even though it seems to be a pillar of light … that's actually not true," Stil said in an interview on the Calgary Eyeopener.

"It's actually an optical illusion that it seems like a beam of light going straight into the air."

Like a rainbow, you could never get closer to or move through these columns of light, Stil says.

The ice crystals hang about halfway between your eyes and the so-called pillar, so if you move, the look of the illusion will change. 

LISTEN | University of Calgary professor explains the science behind light pillars:

You need temperatures below about –20 C for the ice crystals to form, Stil says. But Roland Dechesne, past president of the Royal Astronomical Society of Canada's Calgary centre, says he's seen them at about –11.

He travels into the city for work from Vulcan County — about 80 kilometres southeast of Calgary — and says he sees the light pillars at least a dozen, maybe two dozen, times each winter. 

A sign of waste, light pollution

Because of the city's cold temperatures, the beams aren't uncommon, he says, but as southern Alberta is known for windy conditions, they're not a given. 

Although the beams can be pretty, Dechesne says he actually sees them as a sign of waste.

In order for light to be reflected on the ice crystals, it needs to be angled upward. 

"Typically, when you want to use a light, it's because you want to light the ground, so you want the light to shine below the horizontal," he said.

"When you see a light pillar, it's because there's light shining above the horizontal."

Dechesne says those angled lights are usually a waste of energy, but they can also have impacts on wildlife.

"Most of our songbirds are actually nocturnal migrants, and some of them use visual cues from the night sky to navigate," he said.

"These lights aren't just on in the wintertime when we can see the light pillars. They're on year-round at night."

Despite the light pollution, Stil says he doesn't blame people who think they look spectacular, and the fact that people are interested in them will help raise awareness of the issue.

"The more people become aware, the easier it is to have a discussion about stray light and what it does to the environment."