Thursday, July 19th 2012, 4:35 AM EDT
NOCTILUCENT CLOUDS IN MOTION: "Last night (July 17)some nice noctilucent clouds appeared over Stockholm," reports Swedish photographer Peter Rosen. "Watching NLCs this summer has made me take an interest in their intricate movements--so I decided to create some close-up timelapse movies using a telephoto lens."
"What looked like a serene view from a distance behaves more like a stormy sea with wave after wave rolling in," he observes.
When NLCs first appeared in the 19th century, the mysterious clouds were confined to the Arctic, most often seen in the same places as Northern Lights. In recent years, however, their "habitat" has been expanding, rippling as far south as Colorado, Virginia, Kansas, and Utah. There is growing evidence that the expansion is a sign of climate change, although this remains controversial.
Whatever the reason for the expansion, it means the "stormy sea" could be coming to a sky near you. Observing tips: Look west 30 to 60 minutes after sunset when the sun has dipped 6o to 16o below the horizon. If you see electric-blue waves spreading across the sky, you've probably spotted a noctilucent cloud.
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