MAY is almost done, which means it's time to start optimistically scanning the northern sky after midnight on any clear night, looking for those beautiful, photogenic and frustrating noctilucent clouds again, writes STUART ATKINSON.

NLC are icy clouds so high up in the atmosphere that they are bathed in sunlight long after it's dark here on the ground. Unlike the northern lights, their appearance can't be predicted with any real accuracy; all we can do is look to the north very late on clear summer nights and hope to see them. When they do grace us with their presence they look like swirls, streamers and webs of silvery-blue light, almost like a science fiction film special effect.

Most displays are quite modest, but occasionally an NLC storm appears and then the whole of the northern sky is painted with them, sometimes bright enough to cast shadows. Through binoculars an NLC storm is a stunning sight - you can see the clouds moving in very slow motion, as the upper atmosphere winds blow them around. Such a display can go on right through the night until the light of dawn washes it from the sky.

There are ways of getting a heads up about a display. There are many NLC watchers on social media now, so if you are on Twitter or Facebook you can follow them and read the 'display happening now!' alerts they post whenever NLC appear. If you aren't, all you can do is keep checking the northern sky around midnight on clear nights - and cross your fingers!