Noctilucent Clouds

___________________________________________
Last night, a wide expanse of electric-blue noctilucent clouds (NLCs) appeared over Europe. "It was a beautiful display," says Martin McKenna of Maghera, N.Ireland. "Wonderful twisting bands and waves were begging for attention."

Noctilucent clouds are a mystery. They were first reported in the 19th century after the eruption of super-volcano Krakatoa. In those days the clouds were confined mainly to high latitudes, but they have intensified and spread with sightings in recent years as far south as Colorado and Utah. What causes NLCs? A NASA spacecraft named AIM is in orbit right now on a mission to find out.

One thing is known: Summer is the season for NLCs. Sky watchers in Europe have seen hints of NLC activity in recent weeks, but "this is the finest display so far," says Evans. The cloud was approximately 25o high x 100o wide." Consider it official: NLC season has begun.

more