A video of migrating geese appearing to glow as they fly through the sky over Alberta has captured the internet’s attention.

The clip shows hundreds of dots in a pair of “V” formations, glowing bright yellow as they cruise through the pre-dawn sky.

Andrea Bragg and her husband were passing through Medicine Hat, Alta. on their way to work when they spotted the luminous spectacle overhead.

Bragg said the formation appeared to glow and sparkle, like a bonfire, and at first she thought it might be snow reflecting a nearby light source. They stayed long enough to watch the birds eventually fade back to darkness.

“It was absolutely beautiful,” Bragg recalled in an interview with CTVNews.ca, adding that she was late to work that day. “It was just a once in a lifetime thing -- we’ll never see anything like it again.”

Since Bragg posted the video on Monday, it’s amassed more than 123,000 views and more than 2,000 shares.

Comments on the video speculating about what caused the birds to glow ranged from global warming to aliens, but Dr. Jocelyn Hudon, the curator of Ornithology at the Royal Alberta Museum, said they are snow geese.

Unlike Canada geese, which are largely brown in colour, the lesser-known snow geese are white in colour with black areas on their wings. Hudon says their white feathers cause the birds to reflect a bright light source.

“In order for you to see them, they are reflecting light from somewhere,” he told CTVNews.ca on Friday. “Either that light came from the ground, let’s say from a big city or something, but it could have also come from the moon.”

The footage shows the birds flying over an illuminated greenhouse, but Hudon says the greenhouse likely isn’t the source of the light seen reflecting from the birds.

“That light is nowhere near bright enough to go all the way to the birds and come back,” he said. “It has to be a major source of light, like a city.”

Rod Brook, a wildlife research specialist with the Ontario Ministry of Natural Resources and Forestry, agrees with Hudon that a strong light reflecting on the birds caused the glow.

Snow geese, he says, are more likely than other birds to cause this phenomenon.

“Canada geese and ducks are not likely as reflective because they (have) darker colours underneath,” Brook wrote in an email to CTVNews.ca

Hudon added a recent snowfall in the area likely also contributed.

Dr. Ken Otter, president of the Society of Canadian Ornithologists and professor at the University of Northern British Columbia, says a similar phenomenon occurs at the National September 11 Memorial and Museum in New York City.

As part of the memorial, two beams of light shine into the sky to represent the fallen World Trade Center towers. Birds with white bellies, he says, appear to glow when they fly through the beams of light.

Watch Bragg's video below.

And here is a look at the similar phenomenon in New York City.