This is one of my favourite sites on noctilucent clouds: http://www.nightskyhunter.com/Noctilucent%20Clouds.html http://www.nightskyhunter.com/Noctilucent%20Cl

This is one of my favourite sites on noctilucent clouds: http://www.nightskyhunter.com/Noctilucent%20Clouds.html http://www.nightskyhunter.com/Noctilucent%20Clouds.html It describes what they are, how they differ from normal clouds, and how to recognise them.