They’re back! It’s noctilucent cloud season! Every 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.
Also called “night-shining clouds,” these mysterious clouds glow high in the sky in gleaming colors of silver and blue. And would you believe: they are formed by meteor dust!
When meteors burn up in the upper atmosphere, they leave dust, like smoke. When the hot moist air of summer meets the cold dust from outer space, it forms clouds roughly 50 miles high in the atmosphere. When the light from the rising or setting sun hits these sheets of icy smoke, it glows an eerie blue and seems to ripple like waves across the skies.
Usually, noctilucent clouds are restricted to the most northern skies, but some years, they reach all the way to Middle America.
Noctilucent Clouds seen from Alaska, 2006. Credit: NASA
What are Noctilucent Clouds?
Here are more facts about 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.
Image: The glowing clouds are formed when the light from the setting or rising sun strikes the icy clouds floating high in the atmosphere. Source: NASA and the Naval Research Laboratory, Washington, D.C.
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.
The Krakatoa Volcano of 1885
The first time scientists ever record seeing noctilucent clouds was 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 have spread south. Originally, they were seen only 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.
How to View Noctilucent Clouds
Normally, 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).
However, there have been years when these clouds will reach mid-America, particularly in days following the solstice.
From May through August, search the skies after the Sun is just below the horizon, about 90 minutes 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.
If you are lucky, you will see the rarest clouds on Earth. 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.