NOCTILUCENT CLOUD SEASON BEGINS: Over the weekend, sky watchers in northern Europe and Canada spotted electric-blue tendrils of light reaching out of the western sky at sunset. This signals the beginning of the 2013 season for noctilucent clouds (NLCs). Photographer Silvar Mehik sends this picture from the island of Saaremaa in Estonia:
Noctilucent clouds first appeared in the 19th century after the eruption of super-volcano Krakatoa. At the time, people thoght the clouds were caused by the eruption, but long after Krakatoa's ash settled, the clouds remained. In those days, NLCs were a polar phenomenon confined mainly ro far-northern places such as Scandinavia or Alaska. In recent years they have intensified and spread with sightings as far south as Utah and Colorado. Could this be a sign of climate change? A NASA spacecraft named "AIM" is in orbit to investigate.
NEW! Daily images from AIM are now published here on Spaceweather.com. To find them, look in the left column of the home page and scroll down below the coronal holes.
High latitude sky watchers should be alert for NLCs in the evenings ahead. Observing tips: Look west 30 to 60 minutes after sunset when the sun has dipped 6o to 16o below the horizon. If you see luminous blue-white tendrils spreading across the sky, you've probably spotted a noctilucent cloud.
However, the show's not over. The triangle will stretch and eventually break apart in the nights ahead--and the contortions are worth watching. Keep an eye on the sunset sky all week long. NASA: video, full story.