3.5K views · 445 reactions | The history of UFO sightings in North America goes back nearly 80 years. Explore the timeline of some of the most famous sightings and listen to testimonials from witnesses and the experts who dedicate their careers into uncovering the mysteries behind them. Solve the unknown in the brand new series, UFOs: Investigating The Unknown, Tuesdays at 8pm on National Geographic UK. | National Geographic UK | Facebook