2.2: Noctilucent Clouds Over Sweden

These clouds are Noctilucent clouds; they are the highest clouds found in the mesoshpere. You can only see these clouds when the sun is below the hozion and the lower parts of the atmosphere are in shadow; otherwise, they are too faint to see. This picture was taken around dusk in Vallentuna, Sweden. Scientists believe these clouds are made of small ice-coated particles; however, scientists still do not know much about these types of clouds.