High up in the atmosphere, close to space, Noctilucent clouds start to appear in the summer months. They glow an almost electric blue and are caused by sunlight reflecting off gas particles from meteors that have broken and burned up as they strike the earth’s atmosphere at high speeds. Over the last few years these clouds have become more common and scientists are investigating why.

I see information about these and other atmospheric and astronomical phenomena at Spaceweather.com a fascinating Web page.