Noctilucent clouds are the highest clouds in Earth's atmosphere, being bright
polar mesospheric clouds illuminated by the
Arctic sun from below the horizon, between latitudes of 50° and 70°. They are composed of
water ice crystals up to 100
nm across, forming most frequently in the northern summer at altitudes of 76 to 85 km (47 to 53 mi).Photo:
Martin Koitmäe
Noctilucent clouds are the highest clouds in Earth's atmosphere, being bright
polar mesospheric clouds illuminated by the
Arctic sun from below the horizon, between latitudes of 50° and 70°. They are composed of
water ice crystals up to 100
nm across, forming most frequently in the northern summer at altitudes of 76 to 85 km (47 to 53 mi).Photo:
Martin Koitmäe