The term UFO has become a catch-all for any unidentifiable aerial phenomenon. Floating lights in the sky, strange readings on aircraft radars, and supposed sightings of little green men on the side of the road. How long have humans been seeing things in the sky? You'll learn about the time the White House had a close run-in with UFOs, the origin of the phrase "flying saucer," and the truth behind the UFO sightings in Roswell, New Mexico.