Noctilucent clouds fascinate cloud watchers and scientists as they shine over northern latitudes very high above the Earth, at the edge of space.
These clouds appear during the summertime in the polar latitudes about 80 to 90 km (50 to 56 miles) above the Earth's surface, but they have been spotted in lower latitudes.
The unusual clouds were first noted in 1885, according to NASA, but interest continues to grow as more is learned about them. They are made of tiny ice crystals that glow electric blue when sunlight shines through their cloud-tops.
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"Some of the increase has to be attributed to more people having cameras on their phones so they can quickly snap a picture of those cool-looking phenomena and post it to their social media," AccuWeather Senior Meteorologist Jason Nicholls said.
Yesterday, on flight day 195, I finally saw noctilucent clouds for the very first time! #MarvelsNeverEnd pic.twitter.com/u1RQLt16jD— Sam Cristoforetti (@AstroSamantha) June 7, 2015
Some have tried to attribute these clouds to climate change because they form so high in the atmosphere.
"These clouds can help give a little glimpse as to what is going on in the upper atmosphere. However, a strong correlation between noctilucent clouds and climate change is hard to prove or disprove since we still have more to learn," Nicholls said.
What started out as a two-year scientific mission to study noctilucent clouds continues by NASA.
The Aeronomy of Ice in the Mesosphere satellite is studying the clouds, also known as Polar Mesospheric Clouds.
Researchers last year found that there was a statistical link between winter weather in the United States and the decline in noctilucent clouds over Antarctica, according to NASA.