 There's a good reason why today is World UFO Day. 77 years ago on a June night, a guy named Kenneth Arnold says he witnessed nine high-speed crescent-shaped objects near Mount Rainier in Washington. Two weeks later, a farmer claimed to have found a UFO crash site in what's now the very famous Roswell, New Mexico. But why it's celebrated on July 2nd is as much as a mystery as those little green men think.