Kenneth Arnold UFO sighting, artwork. This sighting of an unidentified flying object (UFO) was made on 24 June 1947 by US businessman and pilot Kenneth Arnold (1915-1984). While flying over the Cascades mountain range in the north-western USA, Arnold reported seeing bright flashes of light, seemingly from crescent-shaped objects flying in formation. Mount Rainier is in the background. It was this sighting that led to the first use of the term 'flying saucer'. Explanations for the sightings included mountain peak mirages, bright clouds, a flock of birds, alien spacecraft, and secret military aircraft.