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UFOs have become a global phenomenon over the last few decades and interest is showing no signs of slowing down.
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75 years ago, pilot Kenneth Arnold sighted several strange objects in the sky near Washington's Mount Rainier.
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Author Nigel Watson has uncovered numerous cases of UFOs being sighted in the early 20th century.
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Amateur pilot Kenneth Arnold kick-started the modern UFO phenomenon after a sighting back in 1947.