This rather poor panorama shows one of the best noctilucent cloud displays I've seen recently (July 2005). Noctilucent clouds, if you haven't heard of them before, are thought to consist of methane that is trapped about 80km up in the atmosphere - much higher than normal weather clouds. They are so high that, in summer, they continue to be lit by the Sun that, from the observing point, is well below the horizon. There is far from complete understanding of these ethereal, electric-blue clouds, but it has been suggested that they are increasing in frequency, and may be early indicators of climate change.