Noctilucent Clouds over Sweden | Earth Science

Noctilucent Clouds over Sweden | Earth Science

Sometimes it is night on the ground but day in the air. As the Earth rotates to eclipse the Sun, sunset rises up from the ground. Therefore, at sunset on the ground, sunlight still shines on clouds above. Under usual circumstances, a pretty sunset might be visible, but unusual noctilucent clouds float so high up they can be seen well after dark. Normally too dim to be seen, they may become visible just after sunset during the summer when illuminated by sunlight from below the horizon. Noctilucent clouds are the highest clouds and are known more technically as polar mesospheric clouds. 

Featured here as they appeared in early August 2026, a network of blue noctilucent clouds was captured in the distant sky above a field of green grass near Linköping, Sweden, with trees in stark silhouette across the horizon. Much about noctilucent clouds has been discovered only in the past two decades, and how they form and evolve remains a topic of active research.

Noctilucent clouds (NLCs), or night shining clouds are tenuous cloud-like phenomena in the upper atmosphere. They consist of ice crystals and from the ground are only visible during astronomical twilight. Noctilucent roughly means "night shining" in Latin. They are most often observed during the summer months from latitudes between ±50° and ±70°. Too faint to be seen in daylight, they are visible only when the observer and the lower layers of the atmosphere are in Earth's shadow while these very high clouds are still in sunlight. Recent studies suggest that increased atmospheric methane emissions produce additional water vapor through chemical reactions once the methane molecules reach the mesosphere—creating, or reinforcing existing, noctilucent clouds.

Sweden, formally the Kingdom of Sweden, is a Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east.

Credit & Copyright V. Höfer, D. Večerník & B. Večerníková
Authors & editors: Robert Nemiroff, Jerry Bonnell, Cecilia Chirenti, Keighley Rockcliffe
A service of the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center, NASA Science Activation & Michigan Technological University (MTU)

Image Date: Aug. 2026
Release Date: Oct. 27, 2026

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