It’s noctilucent cloud season! Every year, from late spring through summer, eerie electric-blue clouds ripple across the night sky. They look alien—resembling something from another world. And that’s not far off. A key ingredient for the mysterious clouds comes from outer space.
As you look at these gleaming, glowing clouds, cool yourself off by realizing that it is made of ice. The hot moist air of summer meets the cold dust from outer space and produces the rarest and most mysterious of night-shining clouds.
What are Noctilucent Clouds?
- Noctilucent clouds or NLCs are Earth’s highest clouds in the sky, literally glowing at the edge of space 50 miles above our planet’s surface. Some call it the great “geophysical light bulb.”
- They exist only in the atmosphere’s mesosphere layer, a high cold layer that is, according to NASA, “one hundred million times dryer than air from the Sahara desert.”
- They are the newest of all the clouds that we observe. They were first seen in 1885, after the famous explosion of Krakatoa volcano. The volcanic dust filtered out incoming sunlight, forming gorgeous fire-red sunsets. Watching sunsets became an international fad. Then, scientists noticed that after the sun set, mysterious glowing blue clouds began to spread through the skies.
- Strangely, even after Krakatoa’s volcanic debris settled, the clouds remained. Indeed they spread. Originally, they could only be seen in the most northern skies of Canada, Europe and Siberia. Now you can see them in the night skies of Colorado and Virginia. No one knows why they are spreading.
Noctilucent Clouds seen from Alaska, 2006. Credit: NASA
How do Noctilucent Clouds Form?
Clouds are made of water and particles. In the lower atmosphere, water molecules attach to the dust in the air and form droplets. As these droplets float through the sky, too light to fall, they collect into clouds. Scientists were mystified. How could dust get fifty miles high into the air?
This August, data from NASA’s AIM spacecraft has finally found out—most of the dust is from outer space!
As meteors plunge into Earth’s atmosphere, they burn up. Only a few reach the surface of the Earth.
The bits of “meteor smoke”, the microscopic dust, floats in the dry upper atmosphere, slowly collecting water molecules and forming ice crystals smaller than the particles in cigarette smoke.
Noctilucent clouds as seen from space by astronauts aboard the International Space Station (ISS) in 2013.
They only form in summer, when hot moist air rises and a few, very few, water molecules rise high enough to cling to the drifting space dust. Then they form glittering sheets of ice, reflecting the lights of the setting sun with an eerie glittering blue light.
How to See Noctilucent Clouds
First, you do need to live at a relatively high latitude on Earth to see them: between about 45° and 60° North or South latitude. In North America, this covers Canada plus the northern-tier Unites States (parts Washington, Oregon, Montana, Idaho, Minnesota, North Dakota, Michigan, Wisconsin, North Dakota, New York, Vermont, New Hampshire, and Maine).
From May through August, search the skies about 90 minutes to two hours after the sun sets. Noctilucent clouds are primarily visible when the sun is just below the horizon because the sunlight can still illuminate these high-altitude clouds, causing them to shine in the night sky.
But even if you don’t live at these latitudes, it’s pretty cool to discover there are luminous clouds that come from outer space!
Learn more about basic types of clouds.