Noctilucent clouds above the Kadoelenwerf by Jeroen de Jongh Photography

About "Noctilucent clouds above the Kadoelenwerf"

by Jeroen de Jongh Photography

About the artwork

Noctilucent clouds are a type of clouds that occur at about 75 to 85 kilometers altitude, much higher than ordinary clouds, which reach an altitude of about 20 kilometers at most. After sunset, those high clouds reflect sunlight for a while. The normal clouds, that we usually see, are in a darker colour and turn first red and then dark grey after sunset. The shining night clouds remain white, yellow-orange or light blue. The stars remain visible in these thin clouds.

In May, June and July, the northern sky may be lit up by these clouds with a silvery sheen for some time after sunset or before sunrise. In these months the sun is low below the northern horizon, so these clouds are lit by the sun from below, as it were. The cloud strands have a ribbed or fibrous structure. They are quite rare and occur irregularly: sometimes they can be seen several times in one month alone, but many a summer passes without them.

The formation of these nocturnal clouds is related to numerous extremely small particles in the upper layers of the atmosphere. These particles can be dust from meteorites, for example. However, such particles alone are not enough: water vapour and very low temperatures between -90 and -145 degrees Celsius are also required. A layer of ice then forms on the particles, just like frost on the earth's surface. Sunlight is reflected by the ice that surrounds the particles.