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NASA's AIM spacecraft is in Earth orbit today following a flawless Wednesday afternoon launch aboard an Pegasus XL rocket. AIM is on a mission to study mysterious noctilucent clouds, such as these photographed by Jan Koeman from his home in the Netherlands in June 2005:

Noctilucent clouds ("NLCs" for short) were first noticed in the 19th century following the eruption of the Krakatoa volcano. After sunset, electric-blue tendrils would spread across the western sky, mesmerizing onlookers. At first scientists thought the clouds were a side-effect of the eruption, but long after Krakatoa's dust has settled, the clouds are still here. Indeed, they are becoming more widespread. Originally confined to high latitudes such as Canada and Scandinavia, NLCs have been seen in recent years as far south as Viriginia and Colorado.