Mysterious Electric Blue Clouds Appear Again Over the Poles [Earth]

Every year around this time, mysterious electric blue clouds appear over the North and South pole. They are called noctilucent clouds and they can only be seen in deep twilight, when the Sun is below the horizon. According to NASA, "their origin is still largely a mystery": More »

Source: http://feeds.gawker.com/~r/gizmodo/full/~3/r0j55mi5rqw/mysterious-electric-blue-clouds-appear-again-over-the-poles

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