In France, yesterday was Bastille Day, and the heavens themselves joined the party. "As we celebrated the storming of the Bastille on July 14th, noctilucent clouds (NLCs) stormed the sky of Paris!" reports Olivier Lagrave who photographed the Eiffel Tower framed in electric blue.
"The display was so breathtaking (my first actually) that I almost forgot to watch the fireworks," he says.
Noctilucent clouds are seldom seen as far south as France -- not to mention seen through fireworks. But the display wasn't over when Bastille Day ended. By sunrise on July 15th, the mysterious clouds had invaded the United States. Mike Hollingshead sends this photo from Blair, Nebraska:
"I've never seen noctilucent clouds before, even though I am often out looking," he says. "These were wonderful." Similar reports have poured in from Oregon, Washington, Idaho, South Dakota, central California and possibly northern Nevada.
These sightings are significant because they come from places so far south. When noctilucent clouds first appeared in the late 19th century, they were confined to latitudes above 50o N (usually far above). The latitude of Blair, Nebraska, is only 41°30' N. No one knows why NLCs are expanding their range in this way; it's one of many unanswered questions about the mysterious clouds. -- SpaceWeather
Noctilucent clouds, are tenuous cloud-like phenomena that are the "ragged-edge" of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. The name means roughly night shining in Latin. They are most commonly observed in the summer months at latitudes between 50° and 70° north and south of the equator.
They are the highest clouds in the Earth's atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometers (47 to 53 mi). They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth's shadow. Noctilucent clouds are not fully understood and are a recently discovered meteorological phenomenon; there is no evidence that they were observed before 1885. -- Wikipedia
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