The first UFO sighting was at 1947. Kenneth A. Arnold, the owner of a fire fighting equipment company in Boise, Idaho, USA, is also a civil aviation pilot. Arnold later described these flying objects as "flat as pie plates", and they could turn at will when flying, "like plates skimming over the water".
So far, there is no evidence that UFOs come from extraterrestrial civilization that can be widely accepted by the scientific community. Some people think that UFO may be purely a psychological phenomenon, which comes from the brain of an individual or a group of people. UFO phenomenon is often intertwined with people's spiritual and psychological experience, and there may be some connection between UFO phenomenon and unexplored areas of human brain.
The vast sky has always stimulated human imagination: atmospheric anomalies, biology, optical illusions, aurora, meteor showers and distant supernovae that can only be named by a few names ... Even in this era of advanced technology, there are still too many natural phenomena that we can't explain.