Noctilucent clouds (NLC) are generally seen for a few weeks either side of the summer solstice primarily at latitudes between 50 and 60 degrees when
the sun is between 6 and 16 degrees below the horizon, this corresponding to the midnight hours. Under these conditions the NLC are sufficiently high
to still be illuminated directly by sunlight
The clouds were first observed above polar regions in 1885 - suggesting they may have been caused by the eruption of Krakatoa two years before. But
they have spread to latitudes as low as 40° in recent years. "They're also getting brighter, and each year there are more of them than in the
Solar physicist Dean Pesnell of the Goddard Space Flight Center says "We're experiencing a very deep solar minimum,". "This is the quietest sun
we've seen in almost a century," agrees sunspot expert David Hathaway of the Marshall Space Flight Center
Increasing range of Noctilucent clouds, the first signs of an approaching ice age.
NLCs INVADE THE USA:
On July 15th, a wave of intense noctilucent clouds (NLCs) descended over the continental United States. "They were so bright, I would have assumed
the dawn was imminent, only it was an hour and a half before sunrise!" The latitude of the Colorado sighting is only 39° N
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