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7/17/2009

Strange Cloud Observations

The heavens have been really showing off these past few weeks -- what with volcanic clouds, blue moons, rainbow clouds, and UW-shaped lightning. Tuesday night was no different. Astute observers from around the northern latitudes of the world noticed a dazzling display of "noctilucent" clouds. They are clouds at the very edge of space, hundreds of thousands of feet in the air. The air is very cold and very dry at that level of the atmosphere, but in the summer time, the rising air from the hotter surface can gradually push a little water moisture to those space-high altitudes (that's why they're seen only in the summer). Scientists are still not quite sure of all the details that cause the clouds to form, although the glow is from simple sunlight -- the clouds are so high they reflect sunlight even after the sun appears well below the horizon from the ground. There are theories that volcanoes can cause them -- and we just had a big eruption of a volcano in Russia last month. Sightings used to be limited to areas above 50 degrees north latitude, but spaceweather.com says the clouds are being seen at lower and lower latitudes these days -- they've seen it a few times in the U.S. Northwest between 45-48 degrees north, and there was a sighting in Nebraska Tuesday night, which is down at 41 degrees north
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