Starwatch: Why ‘night shine’ clouds at edge of space may be product of pollution

Atmospheric methane and industrial pollutants suggested as reasons for lack of noctilucent cloud sightings before 1885

Late spring, early summer marks the beginning of noctilucent cloud season in the northern hemisphere. The name derives from Latin, where noctilucent means night shine". These beautiful cloud formations can often be seen during the summer months shining with an electric blue colour against the darkening western sky about 30 minutes after the sun sets.

The origin of the noctilucent clouds remains mysterious. They are the highest known clouds in Earth's atmosphere, existing at an altitude of about 80km (50 miles), which is virtually the edge of space. They are regarded as being too high and too tenuous to have any effect on the weather at ground level.