On June 8th and 9th, many people who have never previously heard of “noctilucent clouds” (NLCs) found themselves eagerly taking pictures of them.
“I have never seen clouds like this before! I heard that they may have been seeded by meteoroids,” says Tucker Shannon, who took this picture from Corvallis, Oregon:
That’s correct. NLCs are Earth’s highest clouds. Seeded by meteoroids, noctilucent clouds float at the edge of space more than 80 km above the planet’s surface. The clouds are very cold and filled with tiny ice crystals. When sunbeams hit those crystals, they glow electric-blue.
Noctilucent clouds used to be a polar phenomenon
This past weekend, even veteran observers were stunned by the clouds’ intensity and southern reach. At one point, they were visible in Freedom, Oklahoma (latitude +36.7 N). As far as we know, that is the lowest latitude sighting ever:
Other notable low-latitude sightings include San Francisco, California:
and the Cedar Breaks National Monument in Utah:
Still images of NLCs capture only a fraction of their magic. This short video recorded by Mel Gigg on Youtube shows their hypnotic fine-structured rippling motions:
At present, no one can predict exactly when these noctilucent clouds will re-appear. Recent events suggest that even mid-latitude obervers should be alert.
To obeserve these alien-looking clouds, look west 30 to 60 minutes after sunset when the sun has dipped below the horizon. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud.