[/av_heading] [av_textblock size=” font_color=” color=”] Every summer, something strange and wonderful happens high above the north pole. Ice crystals begin to cling to the smoky remains of meteors, forming electric-blue clouds with tendrils that ripple hypnotically against the sunset sky. Noctilucent clouds-a.k.a. “NLCs”- (or Night Clouds) are a delight for high-latitude sky watchers and the pilots who fly at night in the northern part of the world.
The clouds can be seen quite good from the cockpit. They appear only a few times a year, so you have to be lucky to see them.
Noctilucent clouds are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space more than 80 km above Earth’s surface. The clouds are very cold and filled with tiny ice crystals. When sunbeams hit those crystals, they glow electric-blue.
Noctilucent clouds are a mystery dating back to the late 19th century. Northern sky watchers first noticed them in 1885 about two years after the eruption of Krakatoa. Ash from the Indonesian volcano caused such splendid sunsets that evening sky watching became a worldwide pastime. Scientists of the day guessed they were some manifestation of volcanic dust.
Eventually Krakatoa’s ash settled and the sunsets faded, but strangely the noctilucent clouds didn’t go away. They’re still present today, stronger than ever. Researchers aren’t sure what role Krakatoa’s ash played in those early sightings.
One thing is clear, the dust behind the clouds we see now is space dust. In the past, NLCs were a polar phenomenon confined mainly to the Arctic. In recent years they have intensified and spread with sightings as far south as Utah and Colorado. This could be a sign of increasing greenhouse gases in Earth’s atmosphere.
“Data from AIM show that NLCs are like a great “geophysical light bulb.” They turn on every year in late spring, reaching almost full intensity over a period of no more than 5 to 10 days.” (NASA)
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