Tendrils of electric blue light have been seen gently rippling in waves across the sky just after sunset. These are noctilucent clouds, the highest clouds in the atmosphere. So how can clouds form in such an extreme environment? Noctilucent clouds are basically frosted meteor smoke. As meteors burn up in the mesosphere they leave behind smoky trails…

Source: The Times June 25, 2019 23:02 UTC