 An unidentified flying object, or UFO, in its most general definition, is any apparent anomaly in the sky that is not readily identifiable as any known object or phenomenon by visual observation and/or use of associated instrumentation such as radar. These anomalies were referred to popularly as "flying saucers" or "flying discs" during the late 1940s and early 1950s.radarflying saucers  The term "UFO" (or "UFOB") was officially created in 1953 by the United States Air Force (USAF) to replace the more popular terms because of the variety of shapes described other than "discs" or "saucers.United States Air Force

 " As originally defined, the term was restricted to those fraction of cases which remained unidentified after investigation, with USAF interest being for potential national security reasons and/or "technical aspects."  The term UFO became more widespread during the 1950s, at first in professional literature, but later in popular use. UFOs garnered considerable interest during the Cold War, an era associated with a heightened concern for national security.Cold War  " It was stated that a "UFOB" was "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object.

 Reports of UFOs are varied and can include typical saucer shaped metallic discs, anomalous lights, triangular shaped craft and long cigar- shaped objects.  UFOs can exhibit movement or speeds unusual or impossible for conventional aircraft. Some reports recount sightings of several UFOs in formation.  The more people to witness the object the more credibility the report has; reports by astronauts, airline pilots and military personnel are considered to be the most credible of all UFO sightings.

There have been numerous official investigations in to the UFO phenomenon by governments around the world. The British Ministry of Defense maintained a UFO department up until very recently, the United States is also known to have conducted research. Thousands of pages of declassified documents released to the public have also detailed official sightings and investigations from both these countries and others.

 There is little doubt that UFOs exist, however their exact natue, origins and purpose remain open to debate. A popular belief in modern culture is that UFOs are alien in origin and that we are being visited from the stars. Another belief is that at least some UFOs are top secret military aircraft utilising unfamiliar advanced technologies, a spate of triangular UFO sightings for instance was later attributed to tests of the US stealth bomber. The vast majority of UFO sightings do turn out to be explainable, most are attributed to misidentified conventional aircraft, blimps, hot air balloons, chinese lanterns, flares and other mundane things. There are however a small percentage that remain unexplained and it is those sightings that remain the most interesting, to date the UFO phenomenon is one of the most extensively followed of all the world's unexplained mysteries.

: Abductee, Alien, Alien Abduction, Arnold, Kenneth, Brown Mountain Lights, BUFORA, Close Encounters of the First Kind, Close Encounters of the Second Kind, Close Encounters of the Third Kind, Crop Circles, Extraterrestrial Life, Flying Saucer, Foo Fighters, Grey, Hynek Classification System, Lazar, Bob, LITS, Meier, Billy, Miller, Paul, Pleiadian, Pope, Nick, Rods, Roswell Incident, UFO, UFOlogist, UFOlogy AbducteeAlienAlien Abduction Arnold, KennethBrown Mountain Lights BUFORAClose Encounters of the First KindClose Encounters of the Second KindClose Encounters of the Third Kind Crop CirclesExtraterrestrial LifeFlying SaucerFoo FightersGreyHynek Classification SystemLazar, BobLITS Meier, BillyMiller, PaulPleiadianPope, NickRodsRoswell IncidentUFO UFOlogistUFOlogy

Main article: Project SignProject Sign Project Sign in 1948 produced a highly classified finding (see Estimate of the Situation) that the best UFO reports probably had an extraterrestrial explanation; the private but high-level French COMETA study of 1999 reached a similar conclusion. A top secret Swedish military opinion given to the USAF in 1948 stated that some of their analysts believed that the 1946 ghost rockets and later flying saucers had extraterrestrial origins. (For document, see Ghost rockets.) In 1954 German rocket scientist Hermann Oberth revealed that an internal West German government investigation, which he headed, had arrived at an extraterrestrial conclusion, but this study was never made public.Estimate of the SituationGhost rockets Hermann OberthWest German

The study of UFOs has received little support in mainstream scientific literature. Official studies ended in the U.S. in December 1969, following the statement by the government scientist Edward Condon that further study of UFOs could not be justified on grounds of scientific advancement. [11][39] The Condon Report and its conclusions were endorsed by the National Academy of Scientists, of which Condon was a member. On the other hand, a scientific review by the UFO subcommittee of the American Institute of Aeronautics and Astronautics (AIAA) disagreed with Condon's conclusion, noting that at least 30 percent of the cases studied remained unexplained and that scientific benefit might be gained by continued study.Edward Condon [11][39]American Institute of Aeronautics and Astronautics

The Roswell UFO incident (1947) involved New Mexico residents, local law enforcement officers, and the U.S. military, the latter of whom allegedly collected physical evidence from the UFO crash site.Roswell UFO incidentNew Mexico The Mantell UFO incident January 7, 1948Mantell UFO incident The Betty and Barney Hill abduction (1961) was the first reported abduction incident.Betty and Barney Hill abduction In the Kecksburg UFO incident, Pennsylvania (1965), residents reported seeing a bell shaped object crash in the area. Police officers, and possibly military personnel, were sent to investigate.Kecksburg UFO incident The Travis Walton abduction case (1975): The movie Fire in the Sky (1993) was based on this event, but embellished greatly the original account.Travis Walton Fire in the Sky The "Phoenix Lights" March 13, 1997Phoenix Lights

Studies show that after careful investigation, the majority of UFOs can be identified as ordinary objects or phenomena. The most commonly found identified sources of UFO reports are:  Astronomical objects (bright stars, planets, meteors, re-entering man-made spacecraft, artificial satellites, and the Moon)spacecraft artificial satellitesMoon  Aircraft (aerial advertising and other aircraft, missile launches)aerial advertisingmissilelaunches