The season for noctilucent clouds is upon us once again. Around 1.5 hours after sunset, their silvery veils appear low on the northern horizon. They are a real sight to behold on short summer nights.

These clouds are made up of tiny ice crystals and form high above the usual weather clouds, at an altitude of around 80 km.

Up there, temperatures can drop below minus 100 degrees. They resemble fine waves and ribbed structures.

Because the sun remains just below the horizon at night, the clouds continue to shimmer even when it has long since grown dark on the ground. Strong high-altitude winds constantly distort and reshape the silvery veils.

However, noctilucent clouds do not appear every night and as with any high-altitude event, clear skies are needed for this celestial spectacle.