Yellowknife (Jan 26/05) - The aurora borealis isn't the only thing that lights up the sky when it turns cold. According to Yvonne Bilan-Wallace, a meteorologist with the Arctic Weather Centre in Edmonton, sun dogs, also called mock suns, occur when the weather turns cold enough to freeze water vapour in the air into ice crystals.

Sunlight refracts off the crystals, creating a halo around the sun and often a pair of luminescent orbs on either side of it.

"It's really just atmospheric optics," said Bilan-Wallace.

"Cold atmosphere, ice crystals and the wonderful things light will do when it tries to go through crystalline objects."

The one myth that accompanies sun dogs is the belief that they only appear when a storm is on the way.

Bilan-Wallace said, however, that mainly they're just a sign that it's very, very cold out.

"They're not that uncommon in the North," said Bilan-Wallace. "Anytime it gets really cold."

Yosuke Fukushima, a tourism operator with Canadian Ex Aurora Tours, said a lot of his Japanese guests mistake them for rainbows.

He said sun dogs do occur in Japan, but normally only in the extreme northern part of the country.

"The sun dog is quite different from a rainbow," said Fukushima. "It's always the opposite from the sun."

When asked if he thought sun dogs had any tourism potential to go along with the already famous Northern Lights that bring hundreds of Japanese visitors to Yellowknife every winter, Fukushima said he doubted it.

"They don't have any interest in sun dogs, just aurora borealis," said Fukushima.

"They just see the sky at night time. In the day time, they're sleeping or looking for souvenirs."