The science behind a Yellowknife man's breathtaking aurora video

A video shot by Yellowknife man David Yaurecently caught the attention of thousands of friends and aurora aficionados on Facebook.

"That night Ifelt like the light was coming all the way, coming down to me. [It was]totally different from other nights," said Yau, who haslived in Yellowknife for 20 years. "It felt like a dragon was coming down to my face."

Yellowknife falls on the aurora sweet-spot the 67th degree of geomagnetic latitude. Basically, thatmeans it gets one of the best light shows in the country.

The video shows a particularly breathtaking aurora dance this past week. (It also captures the oohs and aahs of several visitors from Hong Kong, clients from Yau's Aurora Ninja tour company.)

So we asked a world aurora expert to find out just what's going on with the ethereal twirls of violets and greens.

"You're looking at a not totally unusual, but fairly unusual, situation where you're getting violet twinges at the bottom of the green arch," explained Eric Donovan, a professor with the Department of Physics and Astronomy at the University of Calgary.

"So that was a particularly energetic event," he said. "It's beautiful."

Think tissues, marbles and a gun

To better explain the science, just imagine a huge pile of tissue paper, says Donovan.

That's the earth's atmosphere.

Now imagine a marble an energy-filled electron that enters the earth's dense atmosphere from outer space.

"When the [electrons] stop, they kind of leave all their energy. So they leave it at whatever altitude they stop at," said Donovan. That energy, reacting with the atmosphere, is what causes the Northern lights.

Now imagine you're throwing marbles on the pile of tissues, or the atmosphere.

"If you were to throw it weakly, it might go an inch in. But if you fire it out of a gun at a very fast speed, it would go all the way through," said Donovan.

The marbles that gently dent the tissues are the green lights; meanwhile, the gunshot marbles that reach deeper into the earth's atmosphere are the violet lights.

Donovan said generally, reactions with oxygen at a height ofaround 100 to200 kilometres is what creates green lights; at higher altitudes, from 150 kilometres up to more than 500 kilometres, people will see red lights. Violet is produced from a reaction withnitrogen at plus or minus a few kilometres from the 95-kilometremark. Below that, the electrons will react to create "very, very energetic X-ray photons," invisible to the eye.

Yau said what was caught on video, was what people who were oohing and aahing saw with their naked eye.

"It was very amazing that night. I felt very special," said Yau.

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