Comet ISON may cause an invisible meteor shower over the Earth when it passes by this year. The dust from the tail will hit Earth's atmosphere and slowly settle to the ground, but it won't be visible. The poles may see some effect though as the dust creates glowing "noctilucent clouds." "Electric-blue ripples over Earth's polar regions might be the only visible sign that a shower is underway," NASA officials said in a release.
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