Earth's rarest clouds were spotted by skywatchers in parts of the western US, Europe and Canada this weekend, and this is the first time they've been sighted in about 15 years.  Depicted are the clouds over London

Rare clouds that glow in the dark can be seen in northern US, Canada and Europe

The rarest clouds on Earth were spotted by sky watchers in parts of the western US, Europe and Canada during the weekend a lively display not seen in about 15 years.

Also known as night-lighting, these clouds glowed a beautiful blue in the sky just after the sun had gone below the horizon.

Reports of the creepy-looking clouds came from OregonWashington, Alberta, UK and Denmark.

Nightly luminescent clouds (NLCs) form in the mesosphere, which is at an elevation of about 50 miles (80 km), making them the tallest in Earth’s atmosphere.

The clouds are made up of ice crystals that become visible at dusk when the sun shines from the horizon.

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Earth’s rarest clouds were spotted by skywatchers in parts of the western US, Europe and Canada this weekend, and this is the first time they’ve been sighted in about 15 years. Depicted are the clouds over London

“There really isn’t anything like them,” the National Weather Service office in Seattle wrote on social media, noting that these are the “most vivid displays of nighttime clouds” seen in the area in decades.

The clouds usually form in late spring and early summer when the lower atmosphere warms.

Atmospheric circulation pushes air upward, which then expands and cools.

Water vapor gets trapped in the clouds, freezes into ice crystals and forms meteoric dust.

Also known as night-lighting, these clouds glowed a beautiful blue in the sky just after the sun had gone below the horizon.  Reports of the eerie-looking clouds came from Oregon, Washington, Alberta, the UK and Denmark (pictured)

Also known as night-lighting, these clouds glowed a beautiful blue in the sky just after the sun had gone below the horizon. Reports of the eerie-looking clouds came from Oregon, Washington, Alberta, the UK and Denmark (pictured)

Nightly luminescent clouds (NLCs) form in the mesosphere, which is at an elevation of about 50 miles (80 km), making them the tallest in Earth's atmosphere.  Image shows Seattle, Washington

Nightly luminescent clouds (NLCs) form in the mesosphere, which is at an elevation of about 50 miles (80 km), making them the tallest in Earth’s atmosphere. Image shows Seattle, Washington

The clouds appear with electric blue and silver streaks and are usually seen at latitudes of 45 and 80 degrees in the Northern and Southern Hemispheres.

And the stunning display can even be seen from space, as astronauts aboard the International Space Station have shared photos of the phenomenon.

There is some belief that climate change also contributes to their development and even that they are seen at latitudes never seen before.

In 2019, for example, they were seen as far south as Joshua Tree, California, suggesting that with more greenhouse gases in the atmosphere, more water vapor is available to form the glowing clouds.

Cora Randall, a professor at the University of Colorado Boulder, told The Washington Post that the increase in clouds could be due to excessive water vapor in the atmosphere from rocket launches.

Another study suggests that the appearance of NLCs fluctuates from year to year and even from decade to decade, but that they have become “significantly” more visible overall.

In 2020, a photographer shared a beautiful image of the phenomenon that gave a 12th-century church a ghostly glow in the early morning hours.

Ollie Tayloran astrophotographer, photographed ‘night-shining’ clouds that illuminated the night sky in the south west of England with spectacular blue and silver streaks.

The clouds appear with electric blue and silver streaks and are usually seen at latitudes of 45 and 80 degrees in the Northern and Southern Hemispheres.  Pictured is Alberta, Canada

The clouds appear with electric blue and silver streaks and are usually seen at latitudes of 45 and 80 degrees in the Northern and Southern Hemispheres. Pictured is Alberta, Canada

On June 22, Taylor set out on a mission to capture nighttime clouds in Dorset, on the south coast of England.

He arrived at Knowlton Church in the middle of a Neolithic monument and began shooting the scene from 2 a.m. to 2:50 a.m.

“It was an excellent night of shooting, arriving in the evening at the location already greeted by night-light clouds, better than I’d seen before in the south of England,” Taylor said.

“The electric blue complemented the misty landscape and eerie structure.”

Taylor tracked the clouds using a combination of several sources, including space weather updates, webcam observations and a Facebook group, according to the European Space Agency.

In 2020, a photographer shared a stunning image of the early morning phenomenon that gave a 12th-century church a ghostly glow (photo)

In 2020, a photographer shared a stunning image of the early morning phenomenon that gave a 12th-century church a ghostly glow (photo)

Nighttime clouds were first described in the mid-19th century after the Krakatoa eruption.

Volcanic ash spread through the atmosphere, providing vivid sunsets around the world and triggering the first known sightings of NLCs.

At first, people thought it was a side effect of the volcano, but long after Krakatoa’s ash settled, the wispy, glowing clouds remained.

WHAT ARE NOCTILUCENT CLOUDS?

Nightly luminescent clouds, also called polar mesospheric clouds, form between 47-53 miles above the Earth’s surface (76-85 km), according to NASA.

Here, water vapor freezes into clouds of ice crystals, which are illuminated when the sun is below the horizon.

They are sown by debris from disintegrating meteors, giving them a ‘shocking’ blue hue as they reflect sunlight.

The clouds are formed during the summer of both the Northern and Southern Hemispheres.

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