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"UFO Classification has six categories: nocturnal lights, daylight discs, radar/visual cases, and close encounters. Almost any type of UFO encounter can fit in one of these categories. Read more about UFO classification."^^<http://www.w3.org/2001/XMLSchema#string>
<http://science.howstuffworks.com/space/aliens-ufos/ufo-classification.htm/printable>