Noctilucent clouds, on the edge of the atmosphere, are increasingly seen outside of polar regions
Something magical appeared at night over London and other parts of Britain on 21 June: ripples of electric blue clouds shimmered in the twilight sky after sunset. These were noctilucent clouds, the highest clouds in the world, more than 80km (50 miles) up on the edge of space, and looked like something from another planet.
Noctilucent clouds form in the mesosphere, the rarefied upper atmosphere with little moisture and intensely low temperatures. The scant water vapour there can freeze on to specks of smoke from meteors burning up in the atmosphere, creating the crystals that form noctilucent clouds. The mesosphere is coldest in summer, allowing the crystals to form.