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© Martin McKenna
New data from NASA's AIM spacecraft show that noctilucent clouds (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.

News flash: The bulb is beginning to glow. The first NLCs of 2009 were sighted over Russia on May 27th, and an even brighter display appeared last night, May 29th, over Denmark and the British Isles. Martin Mc Kenna sends these snapshots from Maghera, Northern Ireland.



"The glowing clouds were more than 100 degrees wide with white, blue and even subtle yellow and green colours," says Mc Kenna. "It was an excellent display to start the season and a good omen of major events to come in the near future!"

The display was also witnessed by from John C Mcconnell of Maghaberry Northern Ireland (photos); Paul Evans of Larne, Northern Ireland (photos); and Ian Brantingham near Banff, Scotland (photos).

There is a well-known correlation between noctilucent clouds and the solar cycle. NLC activity tends to peak during years of solar minimum, possibly because low solar activity allows the upper atmosphere to cool, promoting the growth of ice crystals that make up the clouds. With a century-class solar minimum underway, the stage is set for a good season of NLC watching.

Typically, the first NLCs of spring are wan and pale, followed by better displays as summer unfolds. Browse the galleries from previous years to see what may be in the offing: 2008, 2007, 2006, 2005, 2004, 2003.