Noctilucent Clouds Viewed Above Bonn, Germany

July 09, 2019


Photographer: Thalia Traianou
Summary Authors: Thalia Traianou; Jim Foster

As twilight approached on the date of the summer solstice (June 21) in Bonn, Germany, noctilucent clouds (NLC) began to appear. Noctilucent clouds form in the mesosphere, at an altitude of approximately 55 miles (88 km), typically from late spring through mid-summer. These very high-altitude clouds are visible at latitudes above about 50 degrees north (and south). They take shape when tiny ice crystals, adhering to dust particles left behind from meteors, glow from sunlight that’s still illuminating the upper atmosphere but no longer reaching the surface. On occasion, as on this evening, the appearance of NLC makes the sky seem electric blue. Much of northern and western Europe were treated to this mesmerizing summer solstice display.