From late May through to late August it is possible to spot silvery blue clouds late at night in the northern half of the sky. These are the Noctilucent Clouds, (night shining clouds) and they can only be spotted during the light summer months. Normal clouds lie quite low in the atmosphere only up to around 5 miles up but NLC’s occur much higher (around 50 miles up in the Mesosphere) and are ice crystals that are still in direct sunlight whereas normal clouds are in darkness as to the normal clouds the sun is below the horizon.
They can shift in shape and can be quite impressive or completely absent so conditions in the upper atmosphere have to be right for them to form. Close up pictures often show wave like structures present. NLC’s can appear for several minutes and may even last most of the (short) summer nights or last just an hour or so gradually petering out as morning twilight takes effect.
Below is a gallery of NLC images Paul has taken since 2009, enjoy!