Skip to main content Skip to Search Box

Definition: unidentified flying object (UFO) from Philip's Encyclopedia

Any flying object that cannot readily be explained as either a man-made craft or a natural phenomenon. Reports of UFOs have been documented since ancient times. With the development of aeronautics and astronautics, the number of sightings increased enormously. The majority of supposed UFO sightings have various rational explanations, including spy planes, optical floaters (in the observer's eye), weather balloons, and artificial satellites.


Summary Article: unidentified flying object from The Columbia Encyclopedia

or UFO, an object or light reportedly seen in the sky whose appearance, trajectory, and general dynamic and luminescent behavior do not readily suggest a logical, conventional explanation. Some of these phenomena have been photographed and others correlated with radar echoes. Throughout history there have been reports of strange objects in the sky. In the 20th cent. a number of observers claim to have seen vehicles, or "flying saucers," which some believe are space ships visiting the earth from other planets. Because the objects are often shining and in that part of the sky opposite the sun, most investigators, official and unofficial alike, tend to interpret them as reflections of the sun's rays from airplanes. Some UFOs, when pursued by planes, have proved to be weather balloons or other objects of unquestionably terrestrial origin. Fireballs, meteors, and other meteorological phenomena account for most of the relatively few UFOs that observers report seeing at night. However, there are some sightings that investigators are unable to explain in terms of known phenomena.

  • See Ritchie, D., UFO: The Definitive Guide to Unidentified Flying Objects and Related Phenomena (1994);.
  • Steiger, B., ed., Project Blue Book: The Top Secret UFO Findings Revealed (repr. 1995);.
  • Clark, J., The UFO Book: Encyclopedia of the Extraterrestrial (1997);.
  • Saler, B. et al., UFO Crash at Roswell: The Genesis of a Modern Myth;.
  • Hynek, J. A. et al., Night Siege: The Hudson Valley UFO Sightings (2d ed. 1998);.
  • Hynek, J. A., The UFO Experience: A Scientific Inquiry (1999);.
  • Pope, N., Open Skies, Closed Minds: For the First Time a Government UFO Expert Speaks Out (1999).
The Columbia Encyclopedia, © Columbia University Press 2017

Related Credo Articles

Full text Article unidentified flying objects (UFOs)
The Macmillan Encyclopedia

Objects reported to have been seen in the sky (usually at night) that have not been identified as aircraft, satellites, or known...

Full text Article UFOs
Conspiracy Theories in American History

Although the modern UFO era dates from Kenneth Arnold’s 1947 sighting in Washington State, the first mass sighting of UFOs in the United States...

Full text Article UFO
Chambers Dictionary of the Unexplained

The acronym for ‘unidentified flying object’, in simple terms it applies to any strange object seen in the sky which cannot immediately be...

See more from Credo