Satellite to study source of 'night shining' clouds - space - 12 April 2007 - New Scientist Space

"Iridescent, silvery blue clouds at the edge of space that may be
connected to global warming will be studied by a NASA spacecraft set
to launch on 25 April.

The Aeronomy of Ice in the Mesosphere (AIM) mission will be the first
satellite dedicated to studying the enigmatic phenomenon of
"noctilucent", or night-shining clouds.

The shimmering clouds can be seen glowing just before sunrise or just
after sunset because they are so high up - forming at an altitude of
about 80 kilometres - that the Sun illuminates them from below the
horizon. Watch a video of the clouds shifting in the sky (courtesy of
Hampton University)."

More at http://space.newscientist.com/article.ns?id=dn11594