Astronaut looking at UFOs. Computer artwork of an astronaut during a spacewalk looking at UFOs (unidentified flying objects). They are seen reflected in his visor. These UFOs take the form of flying saucers". Some people believe that such objects are spacecraft carrying aliens which observe and even abduct humans. Sightings of UFOs are common, but most have a simple explanation. High clouds, weather balloons, aircraft and even the Moon have all been mistaken for alien craft. There are a few UFO sightings which have had no explanation."