Noctilucent Clouds
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 are a delight for high-latitude sky watchers, and around the Arctic Circle their season of visibility is always eagerly anticipated.
NASA's AIM spacecraft, which is orbiting Earth on a mission to study noctilucent clouds, started seeing them on May 13th which is a week earlier than expected.
Noctilucent clouds were first noticed in the mid-19th century after the eruption of super-volcano Krakatoa. Volcanic ash spread through the atmosphere, painting vivid sunsets that mesmerized observers all around the world. That was when the NLCs appeared. At first people thought they must be some side-effect of the volcano, but long after Krakatoa's ash settled the noctilucent clouds remained.
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