On July 22, 2008, astronauts from the International Space Station noticed a phenomenon they had never seen before: wisps of electric white-blue clouds streamed over the twilight skies of Mongolia. The clouds, hovering 83 km above Earth’s surface, hung on the edge of space.

The astronauts later learned they had witnessed “noctilucent clouds”.

Noctilucent or “night-shining” clouds were first documented in July 1885 by amateur English astronomer Robert Leslie. He too saw the clouds in a darkening sky.

NASA now investigates this relatively new and rare event, and have found that these events are not as rare as they once were.

Gary Thomas, a professor at the University of Colorado, studies noctilucent clouds (NLCs). “It’s puzzling,” he says. “Noctilucent clouds have not only persisted, but also spread.”

Another relatively new and spreading phenomenon is the mass animal deaths occurring worldwide. Ever since the New Year’s Eve report of 5,000 blackbirds falling from the skies of Beebe, Arkansas, people across the continents wonder why millions of birds, fish, and other wildlife lie dead their beaches and streets. Are NLCs the answer?

Science forums and news reports have recently recast noctilucent clouds as “poisonous space clouds” and “death clouds”.

These reports claim the clouds are made of hydrogen cyanide, a substance fatal to most animals, including humans, if inhaled or ingested. The clouds supposedly form within seconds in a darkening sky. Unsuspecting birds fly into them, inhale the poisonous gas, and die instantly.

That could explain the bird deaths. Or maybe not.

First, no studies from credible news stations or science centres like CNN or NASA have reported finding traces of hydrogen cyanide on the dead birds.

Second, the clouds form near the top of the mesosphere, a layer of the atmosphere that ranges from 50 to 85 km above the Earth’s surface. Most birds don’t fly higher than 4,000 feet, or 1.2 km, and usually prefer staying around 500 feet, or 0.15 km.

Third, scientists believe the clouds consist of frozen water, not hydrogen cyanide.

But scientists do admit the clouds are a peculiar phenomenon. The mesosphere, where temperatures can drop to -90°C, is 100 million times drier than the Sahara desert. What is water doing there?

And why are these clouds appearing more and more often, in places further and further from where they usually originate? The clouds, which were usually seen only at latitudes above 50° (you’d have to travel to places like Scotland or Iceland to see any), are now being reported in mid-latitude areas like Colorado and Oregon.

What caused these clouds to form in the first place? Theories circulate through the news and scientific communities that global warming may be the answer.

For instance, the Indonesian supervolcano Krakatoa erupted two years before the first sighting of the NLCs. It spewed ash over 50 km into the Earth’s atmosphere. Soon after its eruption, magnificent sunsets and electric white-blue clouds appeared during twilight periods. But even after the volcanic ash cleared, the

NLCs remained.

“The first sightings do coincide with the Industrial Revolution,” says Gary Thomas. “But the connection is controversial.”

The NASA website even explains how global warming warms the troposphere, the layer of the atmosphere closest to Earth, while cooling the mesosphere. Since cold temperatures are needed for these clouds to form, that may explain how they are attaining these freezing ranges. Of course, it still doesn’t explain where the water is coming from.

Until research reveals more about these mystery clouds, scientists and the media will continue to speculate.

But one thing is for sure: if you’re lucky enough to catch a glimpse of these night lights, take lots of pictures.