Noctilucent clouds Calgary Alberta
© The Weather Network
A beautiful display of noctilucent or "night shining" clouds lit up the skies across Calgary on Wednesday night. It's a rare, but dazzling atmospheric phenomenon that is only visible under certain very specific conditions at this time of year.

"They are the highest clouds in the atmosphere, forming from ice crystals about 80 km above the earth's surface in the mesosphere," explains Michael Carter, a meteorologist at The Weather Network. "For comparison, the top of a typical tall thunderstorm cloud is about 12-15 km above the surface."

The ice particles are also 1/1000 the width of a human hair.

According to Carter, they are usually much too faint to be seen, but they can become visible during the twilight hours, as was the case in the Calgary area Wednesday night. This occurs when the setting sun is still illuminating the high atmosphere, while to an observer on the surface the sun is already below the horizon.

"Just unbelievable noctilucent clouds this evening...only seen around this time of year!," tweeted The Weather Network's Kyle Brittain who captured the rare phenomenon in Calgary.

Noctilucent clouds require very cold conditions in the upper atmosphere to form, which most commonly occur in the higher latitudes in the summer.

Though noctilucent clouds are rare, they are not unique to Earth's atmosphere. They have also been observed on Mars by NASA's Curiosity rover.

To learn more about the science behind noctilucent clouds, click here.