Unidentified flying object
An unidentified flying object (UFO), or unidentified anomalous phenomenon (UAP), is any perceived airborne, submerged or transmedium phenomenon that cannot be immediately identified or explained. Upon investigation, most UAPs are identified as known objects or atmospheric phenomena, while a small number remain unexplained.
The celestial phenomenon over Basel in 1566.
1561 celestial phenomenon over Nuremberg as printed in an illustrated news notice.
November 22, 1896 illustration of a "mystery airship" published in The San Francisco Call
November 29, 1896 illustration of another "mystery airship" published in The San Francisco Call
Identification studies of UFOs
Identifying unidentified flying objects (UFOs) is a difficult task due to the normally poor quality of the evidence provided by those who report sighting the unknown object. Observations and subsequent reporting are often made by those untrained in astronomy, atmospheric phenomena, aeronautics, physics, and perception. Nevertheless, most officially investigated UFO sightings, such as from the U.S. Air Force's Project Blue Book, have been identified as being due to honest misidentifications of natural phenomena, aircraft, or other prosaic explanations. In early U.S. Air Force attempts to explain UFO sightings, unexplained sightings routinely numbered over one in five reports. However, in early 1953, right after the CIA's Robertson Panel, percentages of unexplained sightings dropped precipitously, usually being only a few percent in any given year. When Project Blue Book closed down in 1970, only 6% of all cases were classified as being truly unidentified.
Lenticular clouds have been reported as UFOs due to their peculiar shape.
A Fata Morgana of a boat below the horizon produces the illusion of a solid form floating in the sky.