Friday, July 26, 2019


If you want to see night shining (noctilucent) clouds, one thing really helps: night. A dark sky is necessary to see the silvery curls of frosted meteor smoke now rippling around the Arctic Circle. "The night before yesterday I saw my first noctilucent clouds (NLCs) of the season here in Dalarna, Sweden," reports Göran Strand, who took this picture of the display:

"Finally, the nights are getting dark enough here in the north so we can see these beautiful clouds," he says.

NLCs are Earth's highest clouds. They form every year in June and July when wisps of summertime water vapor rise to the top of Earth's atmosphere. Molecules of H2O adhere to specks of meteor smoke, forming ice crystals ~83 km high. When sunbeams hit those crystals, they glow electric-blue.

Normally, the clouds begin to fade in late July. However, nothing about the 2019 NLC season is "normal." This has been a remarkable year for NLCs, with unprecedented sightings as far south as New Mexico and southern California. The usual late-July fade might not happen, after all.

Scandinavian observers should be alert for NLCs as the summer sun fades. The best time to look is just after sunset or before sunrise:

Notice: NASA's AIM spacecraft, launched in 2007 to study noctilucent clouds (NLCs), suffered a minor anomaly last week. Members of the science team are optimistic that normal operations will be restored soon. Meanwhile, there will be a gap in's "Daily Daisy" coverage of NLCs around the north pole.

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