Hi all, as there have been quite a few threads discussing this phenomenon and there have been a lot of recent sightings, I thought it would be good to have one place to discuss and post our sightings.
Noctilucent (night shining) clouds are the highest clouds in Earths atmosphere, made up of water ice crystals located in the Mesosphere. They can only form at temperatures of below about -120C, so mainly form during the summer when the Mesosphere is coldest. Normally NLCs are too faint to be seen and are only visible when illuminated by sunlight from below the horizon (best between 6 and 16 degrees below) and so can only be seen in twilight around sunset and sunrise. They are mainly seen at latitudes of 50 to 65 degrees, rarely at lower latitudes or closer to the poles. For reasons no one understands they seem appear most frequently at times of solar minimum, like this year, so it's as good a time as any to keep a look out!
Found a great
Gallery of photos of recent displays on spaceweather.com
Noctilucent Cloud Photo Gallery -- Summer 2009: Page 7