[MIham] Noctilucent Cloud Season Begins

[Frank]

Space Weather News for May 30, 2009
http://spaceweather.com

FIRST NLCs of 2009:  The first noctilucent clouds (NLCs) of 2009 have been 
sighted over northern Europe. Last night, May 29th, photographers recorded 
wispy electric-blue tendrils spreading across the twilight skies of Denmark, 
Northern Ireland and Scotland. This follows a similar display over Russia on 
May 27th.  These sightings signal the beginning of the 2009 NLC season, 
which is expected to last until late July. Early-season NLCs are usually 
feeble, but these were fairly bright and vibrant, suggesting that even 
better displays are in the offing.  Check today's edition of 
http://spaceweather.com for photos.

Noctilucent clouds are an unsolved puzzle.  They float 83 km above Earth's 
surface at the edge of space itself.  People first noticed NLCs in the late 
19th century. In those days you had to travel to high northern latitudes to 
see them.  In recent years, however, the clouds have been sighted in the 
United States as far south as Oregon, Washington and even Colorado. Climate 
change, space dust, and rocket launches have all been cited as possible 
explanations for the phenomenon. Interestingly, low solar activity seems to 
promote the clouds, so the ongoing deep solar minimum could set the stage 
for a good season in 2009.

The best time to look for NLCs is just after sunset or just before sunrise 
when the sun is between 6 and 16 degrees below the horizon.  That's when the 
geometry is just right for sunlight to illuminate the tiny ice crystals that 
make up the clouds.  Observing tips and sample photos may be found in the 
2008 Noctilucent Cloud Gallery:

http://spaceweather.com/nlcs/gallery2008_page10.htm


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