The short summer nights at latitudes 50 – 65° are best to see our very highest clouds.   Do not give up if further south because in Europe they have been seen over Austria, Hungary, Italy and southern Germany.      In the US, Utah and Colorado have had displays.

NLCs are composed of very small ice crystals some 0.1 micron (1/10,000 mm) diameter. They are lit by the sun which still shines at their altitude of 80-85 km (50-53 miles). They are intensely cold -90 Celsius and below.

To distinguish them from lower clouds look for their skeiny structure (binoculars help) and slow movement.

Richard’s video shows well their eerie twisting motion against a foreground of far lower dark scudding tropospheric clouds.