Last night, a bank of rippling electric-blue noctilucent clouds spilled across the Canadian border into the lower United States

NLCs INVADE THE USA: Last night, a bank of rippling electric-blue noctilucent clouds spilled across the Canadian border into the lower United States. In doing so, the clouds made their farthest excursion of the year away from the Arctic, their usual environment. "These were the most brilliant NLCs I have ever witnessed!" reports Steven Rosenow, who sends this picture from Washington state:

"I took my camera to a spot along Washington's Hood Canal for a panoramic view," says Rosenow. "It was a visually stunning display that stretched as far as the eye could see." NLC reports are also coming in from Oregon, Montana, North and South Dakota, and Minnesota, and in Europe as far south as France. (Stay tuned for updates.)

Back in the 19th century, these mysterious clouds were confined to polar regions. In recent years, however, NLCs have spread toward the equator, appearing in places such as Utah, Colorado, and perhaps even Virginia. Is this a sign of climate change? Some researchers think so. Sky watchers at all latitudes are encouraged to be alert for electric blue just after sunset or before sunrise; observing tips may be found in the 2011 NLC gallery.