UFO

An unidentified flying object (usually abbreviated to UFO or U.F.O.) is any unusual apparent object or phenomenon in the sky whose cause cannot be identified by the observer, or (in a narrower definition) by investigators; though in popular usage it more loosely means alien spacecraft, being one explanation (among several) offered for such sightings.[1] Though UFO sightings have occurred throughout history, modern interest in them dates from World War II, since when governments have investigated UFO reports, often from a military perspective, and UFO researchers have investigated, written about and created organizations devoted to the subject.

Studies have established that the majority of UFOs are observations of some real but conventional object—most commonly aircraft, balloons, noctilucent clouds, nacreous clouds, or astronomical objects such as meteors or bright planets — that have been misidentified by the observer as anomalies, while a small percentage of reported UFOs are hoaxes.[2] However, after excluding these incorrect reports, between 5% and 20% of the total remain unexplained, and so can be classified as unidentified in the strictest sense. Many such reports have been made by trained observers such as pilots, police and the military; some involve radar traces, so not all reports are visual.[3] Proponents of an extraterrestrial hypothesis believe that these unidentified reports are of alien spacecraft, though various other hypotheses have been proposed.

While UFOs have been the subject of extensive investigation by various governments, and some scientists support the extraterrestrial hypothesis, few scientific papers about UFOs have been published in peer-reviewed journals.[4] There has been some debate in the scientific communityabout whether any scientific investigation into UFO sightings is warranted.[5] [6] [7] [8] [9] [10]

UFOs have become a prominent theme in modern culture,[11] and this cultural phenomenon has been the subject of academic research

Terminology
The first widely publicized U.S. sighting, reported by private pilot Kenneth Arnold in June 1947, gave rise to the popular terms "flying saucer" and "flying disc", of which the former is still sometimes used, even though Arnold said the most of the objects he saw were not totally circular and one was crescent-shaped (see Kenneth_Arnold_UFO_sighting for details).

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The term "UFO" was first suggested in 1952 by Cpt. Edward J. Ruppelt, who headed Project Blue Book, then the USAF's official investigation of UFOs. Ruppelt felt that "flying saucer" did not reflect the diversity of the sightings. He suggested that UFO should be pronounced as a word —you-foe. However it is now usually pronounced by forming each letter: U.F.O. His term was quickly adopted by theUnited States Air Force, which also briefly used "UFOB". The Air Force initially defined UFOs as those objects that remain unidentified after scrutiny by expert investigators,<sup class="reference" id="cite_ref-11" style="line-height: 1em; font-weight: normal; font-style: normal; ">[12] though today the term UFO is often used for any unexplained sighting regardless of whether it has been investigated.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Because the term UFO is ambiguous - referring either to any unidentified sighting, or in popular usage to alien spacecraft - and the public and media ridicule sometimes associated with the topic, some investigators now prefer to use other terms such as unidentified aerial phenomenon (or UAP).<sup class="reference" id="cite_ref-12" style="line-height: 1em; font-weight: normal; font-style: normal; ">[13]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The equivalent acronym for UFO in Spanish, Portuguese, French, and Italian is OVNI (Objeto Volador No Identificado, Objeto Voador Não Identificado, Objet volant non identifié or Oggetto Volante Non Identificato).

Early history
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Unexplained aerial observations have been reported throughout history. Some were undoubtedly astronomical in nature: comets, brightmeteors, one or more of the five planets that can be seen with the naked eye, planetary conjunctions, or atmospheric optical phenomenasuch as parhelia and lenticular clouds. An example is Halley's Comet, which was recorded first by Chinese astronomers in 240 B.C. and possibly as early as 467 B.C. Such sightings throughout history were often treated as supernatural portents, angels, or other religiousomens. Some current-day UFO researchers have noticed similarities between some religious symbols in medieval paintings and UFO reports<sup class="reference" id="cite_ref-13" style="line-height: 1em; font-weight: normal; font-style: normal; ">[14] though the canonical and symbolic character of such images is documented by art historians placing more conventional religious interpretations on such images.<sup class="reference" id="cite_ref-14" style="line-height: 1em; font-weight: normal; font-style: normal; ">[15]


 * Shen Kuo (1031–1095), a Song Chinese government scholar-official and prolific polymath inventor and scholar, wrote a vivid passage in his Dream Pool Essays (1088) about an unidentified flying object. He recorded the testimony of eyewitnesses in 11th-century Anhui andJiangsu (especially in the city of Yangzhou), who stated that a flying object with opening doors would shine a blinding light from its interior (from an object shaped like a pearl) that would cast shadows from trees for ten miles in radius, and was able to take off at tremendous speeds.<sup class="reference" id="cite_ref-15" style="line-height: 1em; font-weight: normal; font-style: normal; ">[16]
 * On January 25, 1878, The Denison Daily News wrote that local farmer John Martin had reported seeing a large, dark, circular flying object resembling a balloon flying "at wonderful speed." Martin also said it appeared to be about the size of a saucer, the first known use of the word "saucer" in association with a UFO.<sup class="reference" id="cite_ref-16" style="line-height: 1em; font-weight: normal; font-style: normal; ">[17]
 * On February 28, 1904, there was a sighting by three crew members on the USS Supply 300 miles west of San Francisco, reported byLt. Frank Schofield, later to become Commander-in-Chief of the Pacific Battle Fleet. Schofield wrote of three bright red egg-shaped and circular objects flying in echelon formation that approached beneath the cloud layer, then changed course and "soared" above the clouds, departing directly away from the earth after two to three minutes. The largest had an apparent size of about six suns.<sup class="reference" id="cite_ref-17" style="line-height: 1em; font-weight: normal; font-style: normal; ">[18]
 * 1916 and 1926: The three oldest known pilot UFO sightings, of 1305 cataloged by NARCAP. On January 31, 1916, a UK pilot nearRochford reported a row of lights, like lighted windows on a railway carriage, that rose and disappeared. In January 1926, a pilot reported six "flying manhole covers" between Wichita, Kansas and Colorado Springs, Colorado. In late September 1926, an airmail pilot overNevada was forced to land by a huge, wingless cylindrical object.<sup class="reference" id="cite_ref-18" style="line-height: 1em; font-weight: normal; font-style: normal; ">[19]
 * On August 5, 1926, while traveling in the Humboldt Mountains of Tibet's Kokonor region, Nicholas Roerich reported that members of his expedition saw "something big and shiny reflecting the sun, like a huge oval moving at great speed. Crossing our camp the thing changed in its direction from south to southwest. And we saw how it disappeared in the intense blue sky. We even had time to take our field glasses and saw quite distinctly an oval form with shiny surface, one side of which was brilliant from the sun.”<sup class="reference" id="cite_ref-19" style="line-height: 1em; font-weight: normal; font-style: normal; ">[20] Another description by Roerich was, "...A shiny body flying from north to south. Field glasses are at hand. It is a huge body. One side glows in the sun. It is oval in shape. Then it somehow turns in another direction and disappears in the southwest." <sup class="reference" id="cite_ref-20" style="line-height: 1em; font-weight: normal; font-style: normal; ">[21]
 * In the Pacific and European theatres during World War II, "Foo-fighters" (metallic spheres, balls of light and other shapes that followed aircraft) were reported and on occasion photographed by Allied and Axis pilots. Some proposed Allied explanations at the time includedSt. Elmo's Fire, the planet Venus, hallucinations from oxygen deprivation, or German secret weapon.<sup class="reference" id="cite_ref-21" style="line-height: 1em; font-weight: normal; font-style: normal; ">[22] <sup class="reference" id="cite_ref-22" style="line-height: 1em; font-weight: normal; font-style: normal; ">[23]
 * On February 25, 1942, U.S. Army observers reported unidentified aircraft both visually and on radar over the Los Angeles, Californiaregion. Antiaircraft artillery was fired at what was presumed to be Japanese planes. No readily apparent explanation was offered, though some officials dismissed the reports of aircraft as being triggered by anxieties over expected Japanese air attacks on California. However, Army Chief of Staff Gen. George C. Marshall and Secretary of War Henry Stimson insisted real aircraft were involved. The incident later became known as the Battle of Los Angeles, or the West coast air raid.
 * In 1946, there were over 2000 reports, collected primarily by the Swedish military, of unidentified aerial objects in the Scandinavian nations, along with isolated reports from France, Portugal, Italy and Greece, then referred to as "Russian hail", and later as "ghost rockets", because it was thought that these mysterious objects were possibly Russian tests of captured German V1 or V2 rockets. Although most were thought to be natural phenomena like meteors, over 200 were tracked on radar and deemed to be "real physical objects" by the Swedish military. In a 1948 top secret document, the Swedish military told the USAF Europe in 1948 that some of their investigators believed them to be extraterrestrial in origin.

The Kenneth Arnold sightings
Main article: Kenneth Arnold Unidentified Flying Object SightingThis shows the report Kenneth Arnold filed in 1947 about his UFO sighting.<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The post World War II UFO phase in the United States began with a famous sighting by American businessman Kenneth Arnold on June 24, 1947 while flying his private plane nearMount Rainier, Washington. He reported seeing nine brilliantly bright objects flying across the face of Rainier. This shows Kenneth Arnold holding a picture of a drawing of the crescent shaped UFO he saw in 1947.<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Although there were other 1947 U.S. sightings of similar objects that preceded this, it was Arnold's sighting that first received significant media attention and captured the public's imagination. Arnold described what he saw as being "flat like a pie pan", "shaped like saucers and were so thin I could barely see them… ", "half-moon shaped, oval in front and convex in the rear. … they looked like a big flat disk" (see Arnold's drawing at right), and flew "like a saucer would if you skipped it across the water". (One of the objects, however, he would describe later as crescent-shaped, as shown in illustration at left.) Arnold’s descriptions were widely reported and within a few days gave rise to the terms flying saucer and flying disk.<sup class="reference" id="cite_ref-23" style="line-height: 1em; font-weight: normal; font-style: normal; ">[24] Arnold’s sighting was followed in the next few weeks by hundreds of other reported sightings, mostly in the U.S., but in other countries as well. After reports of the Arnold sighting hit the media, other cases began to be reported in increasing numbers. In one instance a United Airlines crew sighting of nine more disc-like objects over Idaho on the evening of July 4. At the time, this sighting was even more widely reported than Arnold’s and lent considerable credence to Arnold’s report.<sup class="reference" id="cite_ref-24" style="line-height: 1em; font-weight: normal; font-style: normal; ">[25]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">American UFO researcher Ted Bloecher, in his comprehensive review of newspaper reports (including cases that preceded Arnold's), found a sudden surge upwards in sightings on July 4, peaking on July 6–8. Bloecher noted that for the next few days most American newspapers were filled with front-page stories of the new "flying saucers" or "flying discs". Speculation as to what the flying saucers were was rampant in the newspapers. Theories ranged from hallucinations, mass hysteria, optical illusions, hoaxes, reflections off airplanes, unusual atmospheric conditions, and weather balloons to byproducts of atomic testing or U.S./Russian secret weapons, to even more esoteric interdimensional or interplanetary visitors. Reports began to rapidly tail off after July 8,<sup class="reference" id="cite_ref-25" style="line-height: 1em; font-weight: normal; font-style: normal; ">[26] when officials began issuing press statements on the Roswell UFO incident, in which they explained debris found on the ground by a rancher as being that of a weather balloon.<sup class="reference" id="cite_ref-26" style="line-height: 1em; font-weight: normal; font-style: normal; ">[27]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Over several years in the 1960s, Bloecher (aided by physicist James E. McDonald) discovered 853 flying disc sightings that year from 140 newspapers from Canada, Washington D.C, and every U.S. state except Montana.<sup class="reference" id="cite_ref-27" style="line-height: 1em; font-weight: normal; font-style: normal; ">[28] <sup class="reference" id="cite_ref-27" style="line-height: 1em; font-weight: normal; font-style: normal; "> Investigations<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">UFOs have been subject to investigations over the years that vary widely in scope and scientific rigor. Governments or independent academics in United States, Canada, the United Kingdom, Japan, Peru, France, Belgium, Sweden, Brazil, Chile, Uruguay, Mexico, Spain, and the Soviet Union are known to have investigated UFO reports at various times.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Among the best known government studies are the ghost rockets investigation by the Swedish military (1946–1947), Project Blue Book, previously Project Sign and Project Grudge, conducted by the United States Air Force from 1947 until 1969, the secret U.S. Army/Air Force Project Twinkle investigation into green fireballs (1948–1951), the secret USAF Project Blue Book Special Report #14 <sup class="reference" id="cite_ref-28" style="line-height: 1em; font-weight: normal; font-style: normal; ">[29] by the Battelle Memorial Institute, and Brazilian Air Force Operation Saucer (1977). France has had an ongoing investigation (GEPAN/SEPRA/GEIPAN) within its space agency CNES since 1977, as has Uruguay since 1989.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Project Sign in 1948 wrote a highly classified opinion (see Estimate of the Situation) that the best UFO reports probably had an extraterrestrial explanation, as did the private but high-level French COMETA study of 1999. A top secret Swedish military opinion given to the USAF in 1948 stated that some of their analysts believed the 1946 ghost rockets and later flying saucers had extraterrestrial origins. (see Ghost rockets for document). In 1954, German rocket scientist Hermann Oberth revealed an internal West German government investigation, which he headed, that arrived at an extraterrestrial conclusion, but this study was never made public. Classified, internal reports by the Canadian Project Magnet in 1952 and 1953 also assigned high probability to extraterrestrial origins. Publicly, however, Project Magnet, nor later Canadian defense studies, ever stated such a conclusion.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Project Sign was dismantled and became Project Grudge at the end of 1948. Angered by the low quality of investigations by Grudge, the Air Force Director of Intelligence reorganized it as Project Blue Book in late 1951, placing Ruppelt in charge. Blue Book closed down in 1970, using the Condon Commission's negative conclusion as a rationale, ending the official Air Force UFO investigations. However, a 1969 USAF document, known as the Bolender memo, plus later government documents revealed that nonpublic U.S. government UFO investigations continued after 1970. The Bollender memo first stated that "reports of unidentified flying objects that could affect national security… are not part of the Blue Book system," indicating that more serious UFO incidents were already handled outside of the public Blue Book investigation. The memo then added, "reports of UFOs which could affect national security would continue to be handled through the standard Air Force procedures designed for this purpose." <sup class="reference" id="cite_ref-29" style="line-height: 1em; font-weight: normal; font-style: normal; ">[30] In addition, in the late 1960s, there was a chapter on UFOs at the U.S. Air Force Academy in their Space Sciences course, giving serious consideration to possible extraterrestrial origins. When word of the curriculum became public, the Air Force in 1970 put out a statement the book was outdated and that cadets were now being informed of Condon's negative conclusion instead.<sup class="reference" id="cite_ref-30" style="line-height: 1em; font-weight: normal; font-style: normal; ">[31]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The initially classified USAF Regulation 200-2, first issued in 1953 after the Robertson Panel, which first defined UFOs and how information was to be collected, stated explicitly that the two reasons for studying the unexplained cases were for national security reasons and for possible technical aspects involved, implying physical reality and concern about national defense, but without opinion as to origins. (For example, such information would also be considered important if UFOs had a foreign or domestic origin.) The first two known classified USAF studies in 1947 also concluded real physical aircraft were involved, but gave no opinion as to origins. (See American investigations immediately below) These early studies led to the creation of the USAF's Project Sign at the end of 1947, the first semi-public USAF study.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Air Force Regulation 200-2,<sup class="reference" id="cite_ref-31" style="line-height: 1em; font-weight: normal; font-style: normal; ">[32] issued in 1953 and 1954, defined an Unidentified Flying Object ("UFOB") as "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." The regulation also said UFOBs were to be investigated as a "possible threat to the security of the United States" and "to determine technical aspects involved." As to what the public was to be told, "it is permissible to inform news media representatives on UFOB's when the object is positively identified as a familiar object," but "For those objects which are not explainable, only the fact that ATIC [Air Technical Intelligence Center] will analyze the data is worthy of release, due to many unknowns involved." <sup class="reference" id="cite_ref-32" style="line-height: 1em; font-weight: normal; font-style: normal; ">[33] <sup class="reference" id="cite_ref-33" style="line-height: 1em; font-weight: normal; font-style: normal; ">[34]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Allen Hynek was a trained astronomer who participated in Project Bluebook after doing research as a federal government employee. He formed the opinion that some UFO reports could not be scientifically explained. Through his founding of the Center for UFO Studies and participation at CUFOs he spent the rest of his life researching and documenting UFOs. The movie Close Encounters of the Third Kind had a character loosely based on Hynek. Another group studying UFOs is Mutual UFO Network. MUFON is a grass roots based organization known for publishing one of the first UFO investigators handbooks. This handbook went into great detail on how to document alleged UFO sightings.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Jacques Vallée, a scientist and prominent UFO researcher, has argued that most UFO research is scientifically deficient, including many government studies such as Project Blue Book, and that mythology and cultism are frequently associated with the phenomenon. Vallée states that self-styled scientists often fill the vacuum left by the lack of attention paid to the UFO phenomenon by official science, but also notes that several hundred professional scientists continue to study UFOs in private, what he terms the "invisible college". He also argues that much could be learned from rigorous scientific study, but that little such work has been done.<sup class="reference" id="cite_ref-Revelations_10-1" style="line-height: 1em; font-weight: normal; font-style: normal; ">[11]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">There has been little mainstream scientific study of UFOs, and the topic has received little serious attention or support in mainstream scientific literature. Official studies ended in the U.S. in December 1969, subsequent to the statement by Edward Condon that the study of UFOs probably could not be justified in the expectation that science would be advanced.<sup class="reference" id="cite_ref-COMETA_6-1" style="line-height: 1em; font-weight: normal; font-style: normal; ">[7] The Condon report and these conclusions were endorsed by the National Academy of Scientists, of which Condon was a member. However, a scientific review by the UFO subcommittee of the AIAA disagreed with Condon's conclusion, noting that at least 30% of the cases studied remained unexplained, and that scientific benefit might be gained by continued study.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">It has been claimed that all UFO cases are anecdotal<sup class="reference" id="cite_ref-Demon_Haunted_34-0" style="line-height: 1em; font-weight: normal; font-style: normal; ">[35] and that all can be explained as prosaic natural phenomena. On the other hand, it has been argued that there is limited awareness among scientists of observational data, other than what is reported in the popular press.<sup class="reference" id="cite_ref-Revelations_10-2" style="line-height: 1em; font-weight: normal; font-style: normal; ">[11] <sup class="reference" id="cite_ref-FSS_35-0" style="line-height: 1em; font-weight: normal; font-style: normal; ">[36]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">No official government investigation has ever publicly concluded that UFOs are indisputably real, physical objects, extraterrestrial in origin, or of concern to national defense. These same negative conclusions also have been found in studies that were highly classified for many years, such as the UK's Flying Saucer Working Party, Project Condign, the US CIA-sponsored Robertson Panel, the US military investigation into the green fireballs from 1948 to 1951, and the Battelle Memorial Institute study for the USAF from 1952 to 1955 (Project Blue Book Special Report #14).

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Some public government conclusions have indicated physical reality but stopped short of concluding extraterrestrial origins, though not dismissing the possibility. Examples are the Belgian military investigation into large triangles over their airspace in 1989–1991 and the recent 2009 Uruguay Air Force study conclusion (see below).

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Some private studies have been neutral in their conclusions, but argued the inexplicable core cases called for continued scientific study. Examples are the Sturrock Panel study of 1998 and the 1970 AIAA review of the Condon Report.

United States
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">US investigations into UFOs include: <p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Thousands of documents released under FOIA also indicate that many U.S. intelligence agencies collected (and still collect) information on UFOs, including the Defense Intelligence Agency (DIA), FBI, CIA, National Security Agency (NSA), as well as military intelligence agencies of the Army and Navy, in addition to the Air Force.<sup class="reference" id="cite_ref-38" style="line-height: 1em; font-weight: normal; font-style: normal; ">[39]
 * The Interplanetary Phenomenon Unit (IPU), established by the US Army sometime in the 1940s, and about which little is known. In 1987, British UFO researcher Timothy Good received a letter confirming the existence of the IPU from the Army Director of Counter-intelligence, in which it was stated, "… the aforementioned Army unit was disestablished during the late 1950s and never reactivated. All records pertaining to this unit were surrendered to the U.S. Air Force Office of Special Investigations in conjunction with operation BLUEBOOK." The IPU records have never been released.<sup class="reference" id="cite_ref-36" style="line-height: 1em; font-weight: normal; font-style: normal; ">[37]
 * Project Blue Book, previously Project Sign and Project Grudge, conducted by the United States Air Force from 1947 until 1969
 * The secret U.S. Army/Air Force Project Twinkle investigation into green fireballs (1948–1951)
 * Ghost rockets investigations by the Swedish, U.K., U.S., and Greek militaries (1946–1947)
 * The secret CIA Office of Scientific Investigation (OS/I) study (1952–53)
 * The secret CIA Robertson Panel (1953)
 * The secret USAF Project Blue Book Special Report No. 14 by the Battelle Memorial Institute (1951–1954)
 * The Brookings Report (1960), commissioned by NASA
 * The public Condon Committee (1966–1968)
 * The private, internal RAND Corporation study (1968)<sup class="reference" id="cite_ref-37" style="line-height: 1em; font-weight: normal; font-style: normal; ">[38]
 * The private Sturrock Panel (1998)

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The investigation of UFOs has also attracted many civilians, who in the U.S formed research groups such as National Investigations Committee On Aerial Phenomena (NICAP, active 1956–1980), Aerial Phenomena Research Organization (APRO, 1952–1988), Mutual UFO Network (MUFON, 1969–), and Center for UFO Studies (CUFOS, 1973–).

After 1947 sightings
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Following the large U.S. surge in sightings in June and early July 1947, on July 9, 1947, Army Air Force (AAF) intelligence, in cooperation with the FBI, began a formal investigation into selected best sightings with characteristics that could not be immediately rationalized, which included Kenneth Arnold’s and that of the United Airlines crew. The AAF used "all of its top scientists" to determine whether or not "such a phenomenon could, in fact, occur". The research was "being conducted with the thought that the flying objects might be a celestial phenomenon," or that "they might be a foreign body mechanically devised and controlled."<sup class="reference" id="cite_ref-39" style="line-height: 1em; font-weight: normal; font-style: normal; ">[40] Three weeks later in a preliminary defense estimate, the air force investigation decided that, "This ‘flying saucer’ situation is not all imaginary or seeing too much in some natural phenomenon. Something is really flying around."<sup class="reference" id="cite_ref-40" style="line-height: 1em; font-weight: normal; font-style: normal; ">[41]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">A further review by the intelligence and technical divisions of the Air Materiel Command at Wright Field reached the same conclusion, that "the phenomenon is something real and not visionary or fictitious," that there were objects in the shape of a disc, metallic in appearance, and as big as man-made aircraft. They were characterized by "extreme rates of climb [and] maneuverability," general lack of noise, absence of trail, occasional formation flying, and "evasive" behavior "when sighted or contacted by friendly aircraft and radar," suggesting a controlled craft. It was thus recommended in late September 1947 that an official Air Force investigation be set up to investigate the phenomenon. It was also recommended that other government agencies should assist in the investigation.<sup class="reference" id="cite_ref-41" style="line-height: 1em; font-weight: normal; font-style: normal; ">[42]

Project Sign
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">This led to the creation of the Air Force’s Project Sign at the end of 1947, one of the earliest government studies to come to a secret extraterrestrial conclusion. In August 1948, Sign investigators wrote a top-secret intelligence estimate to that effect. The Air Force Chief of Staff Hoyt Vandenberg ordered it destroyed. The existence of this suppressed report was revealed by several insiders who had read it, such as astronomer and USAF consultant J. Allen Hynek and Capt. Edward J. Ruppelt, the first head of the USAF's Project Blue Book.<sup class="reference" id="cite_ref-42" style="line-height: 1em; font-weight: normal; font-style: normal; ">[43]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Another highly classified U.S. study was conducted by the CIA's Office of Scientific Investigation (OS/I) in the latter half of 1952 after being directed to do so by the National Security Council (NSC). They concluded UFOs were real physical objects of potential threat to national security. One OS/I memo to the CIA Director (DCI) in December read, "...the reports of incidents convince us that there is something going on that must have immediate attention... Sightings of unexplained objects at great altitudes and traveling at high speeds in the vicinity of major U.S. defense installations are of such a nature that they are not attributable to natural phenomena or any known types of aerial vehicles." The matter was considered so urgent, that OS/I drafted a memorandum from the DCI to the NSC proposing that the NSC establish an investigation of UFOs as a priority project throughout the intelligence and the defense research and development community. They also urged the DCI to establish an external research project of top-level scientists to study the problem of UFOs, now known as theRobertson Panel, to further analyze the matter. The OS/I investigation was called off after the Robertson Panel's negative conclusions in January 1953.<sup class="reference" id="cite_ref-43" style="line-height: 1em; font-weight: normal; font-style: normal; ">[44]

Condon Committee
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">A public research effort conducted by the Condon Committee for the USAF, which arrived at a negative conclusion in 1968, marked the end of the US government's official investigation of UFOs, though documents indicate various government intelligence agencies continue unofficially to investigate or monitor the situation.<sup class="reference" id="cite_ref-44" style="line-height: 1em; font-weight: normal; font-style: normal; ">[45]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Controversy has surrounded the Condon report, both before and after it was released. It has been claimed that the report was "harshly criticized by numerous scientists, particularly at the powerful AIAA … [who] recommended moderate, but continuous scientific work on UFOs".<sup class="reference" id="cite_ref-COMETA_6-2" style="line-height: 1em; font-weight: normal; font-style: normal; ">[7] In an address made to the AAAS, James E. McDonald stated that he believed science had failed to mount adequate studies of the problem, criticizing the Condon report and prior studies by the US Air Force for being scientifically deficient. He also questioned the basis for Condon's conclusions<sup class="reference" id="cite_ref-default_45-0" style="line-height: 1em; font-weight: normal; font-style: normal; ">[46] and argued that the reports of UFOs have been "laughed out of scientific court."<sup class="reference" id="cite_ref-McDonald_5-1" style="line-height: 1em; font-weight: normal; font-style: normal; ">[6] J. Allen Hynek, an astronomer whose position as USAF consultant from 1948 made him perhaps the most knowledgeable scientist connected with the subject, sharply criticized the report of the Condon Committee and later wrote two nontechnical books that set forth the case for investigating seemingly baffling UFO reports.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Ruppelt recounted his experiences with Project Blue Book in his memoir, The Report on Unidentified Flying Objects (1956).<sup class="reference" id="cite_ref-46" style="line-height: 1em; font-weight: normal; font-style: normal; ">[47]

Notable cases

 * The Battle of Los Angeles in 1942, where unidentified flying objects were sequently thought to be part of a Japanese airstrike.
 * The Roswell Incident involved New Mexico residents, local law enforcement officers, and the US military, the latter of whom allegedly collected physical evidence from the UFO crash site.
 * In the Kecksburg Incident, Pennsylvania residents reported seeing a bell shaped object crash in the area. Police officers, and possibly military personnel, were sent to investigate.
 * The Betty and Barney Hill abduction was the first reported abduction incident.
 * 1975 Travis Walton abduction case: The movie Fire in the Sky was based on this event, but embellished greatly the original account.
 * The "Phoenix Lights" March 13, 1997

Canada
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">In Canada, the Department of National Defence has dealt with reports, sightings and investigations of UFOs across Canada. In addition to conducting investigations into crop circles in Duhamel, Alberta, it still considers "unsolved" the Falcon Lake incident in Manitoba and theShag Harbour incident in Nova Scotia.<sup class="reference" id="cite_ref-47" style="line-height: 1em; font-weight: normal; font-style: normal; ">[48]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Early Canadian studies included Project Magnet (1950–1954) and Project Second Story (1952–1954), supported by the Defence Research Board. These studies were headed by Canadian Department of Transport radio engineer Wilbert B. Smith, who later publicly supported extraterrestrial origins.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">In the Shag Harbour incident, a large object sequentially flashing lights was seen and heard to dive into the water by multiple witnesses. TheRoyal Canadian Mounted Police and many local residents also witnessed a light floating on the water immediately afterward, and a large patch of unusual yellow foam when a water search was initiated. Multiple government agencies were eventually involved in trying to identify the crashed object and searching for it. Canadian naval divers later purportedly found no wreckage. In official documents, the object was called a "UFO" because no conventional explanation for the crashed object was discovered. Around the same time, both the Canadian and US military were involved in another UFO-related search at Shelburne, Nova Scotia, approximately 30 miles from Shag Harbour.

France
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">On March 2007, the French Centre National d'Études Spatiales (CNES) published an archive of UFO sightings and other phenomena online.<sup class="reference" id="cite_ref-48" style="line-height: 1em; font-weight: normal; font-style: normal; ">[49]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">French studies include GEPAN/SEPRA/GEIPAN (1977–), within the French space agencyCNES, the longest ongoing government-sponsored investigation. About 14% of some 6000 cases studied remained unexplained. The official opinion of GEPAN/SEPRA/GEIPAN has been neutral or negative, but the three heads of the studies have gone on record in stating that UFOs were real physical flying machines beyond our knowledge or that the best explanation for the most inexplicable cases was an extraterrestrial one.<sup class="reference" id="cite_ref-49" style="line-height: 1em; font-weight: normal; font-style: normal; ">[50]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The French COMETA panel (1996–1999) was a private study undertaken mostly by aerospace scientists and engineers affiliated with CNES and high-level French Air Force military intelligence analysts, with ultimate distribution of their study intended for high government officials. The COMETA panel likewise concluded the best explanation for the inexplicable cases was the extraterrestrial hypothesis and went further in accusing the United States government of a massive cover-up.<sup class="reference" id="cite_ref-50" style="line-height: 1em; font-weight: normal; font-style: normal; ">[51]

United Kingdom
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The UK's Flying Saucer Working Party published its final report in 1951, which remained secret for over 50 years. The Working Party concluded that all UFO sightings could be explained as misidentifications of ordinary objects or phenomena, optical illusions, psychological delusions or hoaxes. The report stated: "We accordingly recommend very strongly that no further investigation of reported mysterious aerial phenomena be undertaken, unless and until some material evidence becomes available."

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Eight file collections on UFO sightings, dating from 1978 to 1987, were first released on May 14, 2008, to the UK National Archives by theMinistry of Defence.<sup class="reference" id="cite_ref-51" style="line-height: 1em; font-weight: normal; font-style: normal; ">[52] Although kept secret from the public for many years, most of the files have low levels of classification and none are classified Top Secret. 200 files are set to be made public by 2012. The files are correspondence from the public sent to government officials, such as the MoD and Margaret Thatcher. The MoD released the files under the Freedom of Information Act due to requests from researchers.<sup class="reference" id="cite_ref-52" style="line-height: 1em; font-weight: normal; font-style: normal; ">[53] These files include, but are not limited to, UFOs over Liverpool and the Waterloo Bridge in London.<sup class="reference" id="cite_ref-53" style="line-height: 1em; font-weight: normal; font-style: normal; ">[54]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">On October 20, 2008 more UFO files were released. One case released detailed that in 1991 an Alitalia passenger aircraft was approachingHeathrow Airport when the pilots saw what they described as a "cruise missile" fly extremely close to the cockpit. The pilots believed that a collision was imminent. UFO expert David Clarke says that this is one of the most convincing cases for a UFO he has come across.<sup class="reference" id="cite_ref-54" style="line-height: 1em; font-weight: normal; font-style: normal; ">[55]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">A secret study of UFOs was undertaken for the UK’s Ministry of Defence (MoD) between 1996 and 2000 and was code-named Project Condign. The resulting report, titled "Unidentified Aerial Phenomena in the UK Defence Region", was publicly released in 2006, but the identity and credentials of whomever constituted Project Condign remains classified. The report confirmed earlier findings that the main causes of UFO sightings are misidentification of man-made and natural objects. The report noted: "No artefacts of unknown or unexplained origin have been reported or handed to the UK authorities, despite thousands of UAP reports. There are no SIGINT, ELINT or radiation measurements and little useful video or still IMINT." It concluded: "There is no evidence that any UAP, seen in the UKADR [UK Air Defence Region], are incursions by air-objects of any intelligent (extraterrestrial or foreign) origin, or that they represent any hostile intent." A little-discussed conclusion of the report was that novel meteorological plasma phenomenon akin to Ball Lightning are responsible for a small percentage of otherwise inexplicable sightings, especially reports of Black Triangle UFOs.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">In August 2009 The Black Vault internet archive announced the release by the British government of more than 4,000 pages of declassified records.<sup class="reference" id="cite_ref-55" style="line-height: 1em; font-weight: normal; font-style: normal; ">[56] The records include information on the Rendlesham Forest incident, crop circles, a UFO attack on a cemetery and even reports of alien abduction claims.<sup class="reference" id="cite_ref-56" style="line-height: 1em; font-weight: normal; font-style: normal; ">[57]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">On 1 December 2009, the British Ministry of Defense (MoD) quietly closed down its UFO investigations unit. The unit's hotline and email address were suspended by the Ministry of Defense on that date. The MoD said there was no value in continuing to receive and investigate sightings in a release, stating
 * "... in over fifty years, no UFO report has revealed any evidence of a potential threat to the United Kingdom. The MoD has no specific capability for identifying the nature of such sightings. There is no Defence benefit in such investigation and it would be an inappropriate use of defence resources. Furthermore, responding to reported UFO sightings diverts MoD resources from tasks that are relevant to Defence."

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The Guardian reported that the MoD claimed the closure would save the Ministry around £50,000 a year. The MoD said that it would continue to release UFO files to the public through the National Archives.<sup class="reference" id="cite_ref-57" style="line-height: 1em; font-weight: normal; font-style: normal; ">[58]

Notable cases

 * According to records released on August 5, 2010, British wartime prime minister Winston Churchill banned the reporting for 50 years of an alleged UFO incident because of fears it could create mass panic. Reports given to Churchill claimed the incident allegedly involved an RAF reconnaissance plane returning from a mission in France or Germany toward the end of the Second World War. It was over or near the English coastline when it was allegedly suddenly intercepted by a strange metallic object that matched the aircraft's course and speed for a time before accelerating away and disappearing. The plane's crew were reported to have photographed the object, which they said had "hovered noiselessly" near the aircraft, before moving off.<sup class="reference" id="cite_ref-58" style="line-height: 1em; font-weight: normal; font-style: normal; ">[59] According to the documents, details of the coverup emerged when the man wrote to the government in 1999 seeking to find out more about the incident. He described how his grandfather, who served with the Royal Air Force (RAF) in the Second World War, was present when Churchill and U.S. General Dwight Eisenhower discussed how to deal with the UFO encounter.<sup class="reference" id="cite_ref-59" style="line-height: 1em; font-weight: normal; font-style: normal; ">[60] <sup class="reference" id="cite_ref-60" style="line-height: 1em; font-weight: normal; font-style: normal; ">[61] The files come from more than 5,000 pages of UFO reports and letters and drawings from members of the public, as well as questions raised by MPs in Parliament. They are available to download for free for a month from The National Archives website.<sup class="reference" id="cite_ref-61" style="line-height: 1em; font-weight: normal; font-style: normal; ">[62]
 * In April 1957 the West Freugh Incident (named after RAF West Freugh in Scotland, the principal military base involved) occurred. Two unidentified objects flying very high over the UK were tracked by radar operators. The objects were reported to operate at speeds and perform manuveres beyond the capability of any known craft. Also significant is their alleged size which - based on the radar returns - was closer to that of a ship than an aircraft.
 * In the Rendlesham Forest incident of December 1980, US military personnel witnessed UFOs in the forest near the air base at Woodbridge, Suffolk, over a period of three nights. The sighting was the subject of an official memo to the UK’s Ministry of Defence.

Uruguay
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The Uruguayan Air Force has had an ongoing UFO investigations since 1989 and analyzed 2100 cases, of which they consider only 40 (about 2%) definitely lacking any conventional explanation. All files have recently been declassified. The unexplained cases include military jet interceptions, abductions, cattle mutilations, and physical landing trace evidence. Colonel Ariel Sanchez, who currently heads the investigation, summarized their findings as follows: "The commission managed to determine modifications to the chemical composition of the soil where landings are reported. The phenomenon exists. It could be a phenomenon that occurs in the lower sectors of the atmosphere, the landing of aircraft from a foreign air force, up to the extraterrestrial hypothesis. It could be a monitoring probe from outer space, much in the same way that we send probes to explore distant worlds. The UFO phenomenon exists in the country. I must stress that the Air Force does not dismiss an extraterrestrial hypothesis based on our scientific analysis."<sup class="reference" id="cite_ref-62" style="line-height: 1em; font-weight: normal; font-style: normal; ">[63]

Astronomer reports
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The United States Air Force's Project Blue Book files indicate that approximately 1 %<sup class="reference" id="cite_ref-63" style="line-height: 1em; font-weight: normal; font-style: normal; ">[64] of all unknown reports came from amateur and professional astronomers or other users of telescopes (such as missile trackers or surveyors). In 1952, astronomer J. Allen Hynek, then a consultant to Blue Book, conducted a small survey of 45 fellow professional astronomers. Five reported UFO sightings (about 11%). In the 1970s, astrophysicist Peter A. Sturrock conducted two large surveys of the American Institute of Aeronautics and Astronautics andAmerican Astronomical Society. About 5 % of the members polled indicated that they had had UFO sightings.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Astronomer Clyde Tombaugh, who admitted to six UFO sightings, including three green fireballs, supported the Extraterrestrial hypothesis (ETH) for UFOs and stated he thought scientists who dismissed it without study were being "unscientific". Another astronomer was Lincoln LaPaz, who had headed the Air Force's investigation into the green fireballs and other UFO phenomena in New Mexico. LaPaz reported two personal sightings, one of a green fireball, the other of an anomalous disc-like object. (Both Tombaugh and LaPaz were part of Hynek's 1952 survey.) Hynek himself took two photos through the window of a commercial airliner of a disc-like object that seemed to pace his aircraft.<sup class="reference" id="cite_ref-64" style="line-height: 1em; font-weight: normal; font-style: normal; ">[65] Even later UFO debunker Donald Menzel filed a UFO report in 1949.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">In 1980, a survey of 1800 members of various amateur astronomer associations by Gert Helb and Hynek for the Center for UFO Studies(CUFOS) found that 24 % responded "yes" to the question "Have you ever observed an object which resisted your most exhaustive efforts at identification?"<sup class="reference" id="cite_ref-65" style="line-height: 1em; font-weight: normal; font-style: normal; ">[66]

Identification of UFOs
Main article: Identification studies of UFOsFata Morgana, a type of mirage in which objects located below the astronomical horizon appear to be hovering in the sky, may be responsible for some UFO sightings. Fata Morgana can also magnify the appearance of distant objects or distort them to be unrecognizable.<sup class="reference" id="cite_ref-Offical_UFO_Investigations_in_France:_the_GEPAN.2FSEPRA_Project_66-0" style="line-height: 1em; font-weight: normal; font-style: normal; ">[67] <p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Studies show that after careful investigation, the majority of UFOs can be identified as ordinary objects or phenomena (see Identification studies of UFOs). The most commonly found identified sources of UFO reports are: Lenticular clouds have been reported as UFOs due to their peculiar shape.<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">A 1952–1955 study by the Battelle Memorial Institute for the US Air Force included these categories as well as a "psychological" one. However, the scientific analysts were unable to come up with prosaic explanations for 21.5 % of the 3200 cases they examined and 33 % of what were considered the best cases remained unexplained, double the number of the worst cases. (See full statistical breakdown in Identification studies of UFOs). Of the 69 % identifieds, 38 % were deemed definitely explained while 31 % were thought to be "questionable." About 9 % of the cases were considered to have insufficient information to make a determination.
 * Astronomical objects (bright stars, planets, meteors, re-entering man-made spacecraft, artificial satellites, and the moon)
 * Aircraft (Aerial advertising and other aircraft, missile launches)
 * Balloons (weather balloons, prank balloons, large research balloons)
 * Other atmospheric objects and phenomena (birds, unusual clouds, kites, flares)
 * Light phenomena (mirages, Fata Morgana, moon dogs, searchlights and other ground lights, etc.)
 * Hoaxes

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">The official French government UFO investigation (GEPAN/SEPRA/GEIPAN), run within the French space agency CNES between 1977 and 2004, scientifically investigated about 6000 cases and found that 13.5 % defied any rational explanation, 46 % were deemed definitely or likely identifiable, while 41 % lacked sufficient information for classification.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">An individual 1979 study by CUFOS researcher Allan Hendry found, as did other investigations, that only a small percentage of cases he investigated were hoaxes (<1 %) and that most sightings were actually honest misidentifications of prosaic phenomena. Hendry attributed most of these to inexperience or misperception.<sup class="reference" id="cite_ref-67" style="line-height: 1em; font-weight: normal; font-style: normal; ">[68] However, Hendry's figure for unidentified cases was considerably lower than many other UFO studies such as Project Blue Book or the Condon Report that have found rates of unidentified cases ranging from 6 % to 30 %. Hendry found that 88.6 % of the cases he studied had a clear prosaic explanation, and he discarded a further 2.8 % due to unreliable or contradictory witnesses or insufficient information. The remaining 8.6 % of reports could not definitively be explained by prosaic phenomena, although he felt that a further 7.1 % could possibly be explained, leaving only the very best 1.5 % without plausible explanation.

UFO hypotheses
The ext*raterrestrial hypothesis (ETH) is defined by Edward U. Condon in the 1968 Condon Report as "The idea that some UFOs may be spacecraft sent to Earth from another civilization, or on a planet associated with a more distant star", further attributing the popularity of the idea to Donald Keyhoe's UFO book from 1950,<sup class="reference" id="cite_ref-condonsummary_68-0" style="line-height: 1em; font-weight: normal; font-style: normal; ">[69] though the idea clearly predated Keyhoe, appearing in newspapers and various government documents (see immediately below). This is probably the most popular theory among Ufologists. Some private or governmental studies, some secret, have concluded in favor of the ETH, or have had members who disagreed with official conclusions against the conclusion by committees and agencies to which they belonged.<sup class="reference" id="cite_ref-69" style="line-height: 1em; font-weight: normal; font-style: normal; ">[70] <sup class="reference" id="cite_ref-70" style="line-height: 1em; font-weight: normal; font-style: normal; ">[71] <sup class="reference" id="cite_ref-71" style="line-height: 1em; font-weight: normal; font-style: normal; ">[72] <sup class="reference" id="cite_ref-72" style="line-height: 1em; font-weight: normal; font-style: normal; ">[73] <sup class="reference" id="cite_ref-73" style="line-height: 1em; font-weight: normal; font-style: normal; ">[74] <sup class="reference" id="cite_ref-74" style="line-height: 1em; font-weight: normal; font-style: normal; ">[75] <sup class="reference" id="cite_ref-75" style="line-height: 1em; font-weight: normal; font-style: normal; ">[76]
 * The UFO Hostility Hypothesis is inside the extraterrestrial hypothesis. It says that the extraterrestrial beings that travel in the UFOs, or most of them, are hostile. The hypothesis comes because of the Cattle Mutilations and the observations made by Wilhelm Reich amdJerome Eden during their experiments with the Cloudbuster.<sup class="reference" id="cite_ref-76" style="line-height: 1em; font-weight: normal; font-style: normal; ">[77]
 * The interdimensional hypothesis (IDH or IH) says that UFOs are objects crossing over from other dimensions or parallel universe, popularly proposed by Jacques Vallée,<sup class="reference" id="cite_ref-valleedimensions_77-0" style="line-height: 1em; font-weight: normal; font-style: normal; ">[78] though also predating him.
 * The paranormal/occult hypothesis is a variant of the interdimensional hypothesis, invoked to explain so-called paranormal aspects sometimes associated with UFO reports.
 * The psychosocial hypothesis, that what people report as UFO experiences is the result of psychological misperception mechanisms and is strongly influenced by popular culture.
 * That UFOs represent poorly understood or still unknown natural phenomena, such as ball lightning or sprites.<sup class="reference" id="cite_ref-78" style="line-height: 1em; font-weight: normal; font-style: normal; ">[79]
 * The earthquake lights/tectonic strain hypothesis: UFOs are caused by strains in Earth's crust near earthquake faults, which can also supposedly induce hallucinations.
 * That UFOs are military flying saucers, top secret or experimental aircraft unfamiliar to most people.<sup class="reference" id="cite_ref-79" style="line-height: 1em; font-weight: normal; font-style: normal; ">[80]

Associated claims
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Besides anecdotal visual sightings, reports sometimes include claims of other kinds of evidence, including cases studied by the military and various government agencies of different countries (such as Project Blue Book, the Condon Committee, the French GEPAN/SEPRA, and Uruguay's current Air Force study).

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">A comprehensive scientific review of cases where physical evidence was available was carried out by the 1998 Sturrock UFO panel, with specific examples of many of the categories listed below.<sup class="reference" id="cite_ref-80" style="line-height: 1em; font-weight: normal; font-style: normal; ">[81]
 * Radar contact and tracking, sometimes from multiple sites. These have included military personnel and control tower operators, simultaneous visual sightings, and aircraft intercepts. One such recent example were the mass sightings of large, silent, low-flying black triangles in 1989 and 1990 over Belgium, tracked by NATO radar and jet interceptors, and investigated by Belgium's military (included photographic evidence).<sup class="reference" id="cite_ref-81" style="line-height: 1em; font-weight: normal; font-style: normal; ">[82] Another famous case from 1986 was the JAL 1628 case over Alaska investigated by the FAA.
 * Photographic evidence, including still photos, movie film, and video.
 * Claims of physical trace of landing UFOs, including ground impressions, burned and/or desiccated soil, burned and broken foliage, magnetic anomalies<sup class="noprint Inline-Template" style="line-height: 1em; white-space: nowrap; " title="The text preceeding this tag needs specification from February 2009">[specify], increased radiation levels, and metallic traces. See, e. g. Height 611 UFO Incident or the 1964 Lonnie Zamora's Socorro, New Mexico encounter of the USAF Project Blue Book cases). A well-known example from December 1980 was theUSAF Rendlesham Forest Incident in England. Another occurred in January 1981 in Trans-en-Provence and was investigated byGEPAN, then France's official government UFO-investigation agency. Project Blue Book head Edward J. Ruppelt described a classic 1952 CE2 case involving a patch of charred grass roots.
 * Physiological effects on people and animals including temporary paralysis, skin burns and rashes, corneal burns, and symptoms superficially resembling radiation poisoning, such as the Cash-Landrum incident in 1980.
 * Animal/cattle mutilation cases, that some feel are also part of the UFO phenomenon.
 * Biological effects on plants such as increased or decreased growth, germination effects on seeds, and blown-out stem nodes (usually associated with physical trace cases or crop circles)
 * Electromagnetic interference (EM) effects. A famous 1976 military case over Tehran, recorded in CIA and DIA classified documents, was associated with communication losses in multiple aircraft and weapons system failure in an F-4 Phantom II jet interceptor as it was about to fire a missile on one of the UFOs.<sup class="reference" id="cite_ref-82" style="line-height: 1em; font-weight: normal; font-style: normal; ">[83]
 * Apparent remote radiation detection, some noted in FBI and CIA documents occurring over government nuclear installations at Los Alamos National Laboratory and Oak Ridge National Laboratory in 1950, also reported by Project Blue Book director Ed Ruppelt in his book.
 * Claimed artifacts of UFOs themselves, such as 1957, Ubatuba, Brazil, magnesium fragments analyzed by the Brazilian government and in the Condon Report and by others. The 1964 Socorro/Lonnie Zamora incident also left metal traces, analyzed by NASA.<sup class="reference" id="cite_ref-83" style="line-height: 1em; font-weight: normal; font-style: normal; ">[84] A more recent example involves "the Bob White object" a tear drop shaped object recovered by Bob White and was featured in the TV showUFO Hunters.
 * Angel hair and angel grass, possibly explained in some cases as nests from ballooning spiders or chaff.

Reverse engineering
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Attempts have been made to reverse engineer the possible physics behind UFOs through analysis of both eyewitness reports and the physical evidence, on the assumption that they are powered vehicles. Examples are former NASA and nuclear engineer James McCampbell in his book Ufology, NACA/NASA engineer Paul R. Hill in his book Unconventional Flying Objects, and German rocketry pioneer Hermann Oberth. Among subjects tackled by McCampbell, Hill, and Oberth was the question of how UFOs can fly at supersonic speeds without creating a sonic boom. McCampbell's proposed solution is microwave plasma parting the air in front of the craft. In contrast, Hill and Oberth believed UFOs utilize an as yet unknown anti-gravity field to accomplish the same thing as well as provide propulsion and protection of occupants from the effects of high acceleration.<sup class="reference" id="cite_ref-84" style="line-height: 1em; font-weight: normal; font-style: normal; ">[85]

Ufology
Main article: Ufology<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Ufology is a neologism describing the collective efforts of those who study UFO reports and associated evidence.

Researchers
Main article: List of Ufologists===Sightings=== Main article: List of sightings of unidentified flying objects===Organizations=== Main article: UFO organizations===Categorization=== Some ufologists recommend that observations be classified according to the features of the phenomenon or object that are reported or recorded. Typical categories include:*Saucer, toy-top, or disk-shaped "craft" without visible or audible propulsion. (day and night) <p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Popular UFO classification systems include the Hynek system, created by J. Allen Hynek, and the Vallée system, created by Jacques Vallée.
 * Large triangular "craft" or triangular light pattern, usually reported at night.
 * Cigar-shaped "craft" with lighted windows (Meteor fireballs are sometimes reported this way, but are very different phenomena).
 * Other: chevrons, (equilateral) triangles, crescent, boomerangs, spheres (usually reported to be shining, glowing at night), domes, diamonds, shapeless black masses, eggs, pyramids and cylinders, classic "lights".

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Hynek's system involves dividing the sighted object by appearance, subdivided further into the type of "close encounter" (a term from which the film director Steven Spielberg derived the title of his UFO movie, "Close Encounters of the Third Kind").

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Jacques Vallée's system classifies UFOs into five broad types, each with from three to five subtypes that vary according to type.

Scientific skepticism
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">A scientifically skeptical group that has for many years offered critical analysis of UFO claims is the Committee for Skeptical Inquiry (CSI).

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Responding to local beliefs that "extraterrestrial beings" in UFOs were responsible for crop circles appearing in Indonesia, the government and the National Aeronautics and Space Agency (Lapan) described them as "man-made". Thomas Djamaluddin, research professor of astronomy and astrophysics at Lapan stated: "We have come to agree that this 'thing' cannot be scientifically proven. A professor at the Indonesian National Aeronautics and Space Agency put UFOs in the category of pseudoscience."<sup class="reference" id="cite_ref-Krismantari_85-0" style="line-height: 1em; font-weight: normal; font-style: normal; ">[86]

Conspiracy theories
Main article: UFO conspiracy theory<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">UFOs are sometimes an element of conspiracy theories in which governments are allegedly intentionally "covering up" the existence of aliens or sometimes collaborating with them. There are many versions of this story; some are exclusive, while others overlap with various other conspiracy theories.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">In the U.S., an opinion poll conducted in 1997 suggested that 80 % of Americans believed the U.S. government was withholding such information.<sup class="reference" id="cite_ref-86" style="line-height: 1em; font-weight: normal; font-style: normal; ">[87] <sup class="reference" id="cite_ref-cnn97_87-0" style="line-height: 1em; font-weight: normal; font-style: normal; ">[88] Various notables have also expressed such views. Some examples are astronauts Gordon Cooper and Edgar Mitchell, Senator Barry Goldwater, Vice Admiral Roscoe H. Hillenkoetter (the first CIA director), Lord Hill-Norton (former British Chief of Defense Staff and NATO head), the 1999 high-level French COMETA report by various French generals and aerospace experts, and Yves Sillard (former director of the French space agency CNES, new director of French UFO research organization GEIPAN).<sup class="reference" id="cite_ref-88" style="line-height: 1em; font-weight: normal; font-style: normal; ">[89]

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">It has also been suggested by a few paranormal authors that all or most human technology and culture is based on extraterrestrial contact. See also ancient astronauts.

Allegations of evidence suppression
See also: Disclosure Project, Men in Black, and Brookings Report<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">There have been allegations of suppression of UFO related evidence for many decades. There are claims that physical evidence might have been removed and/or destroyed/suppressed by some governments.

Famous hoaxes
Main article: List of UFO-related hoaxes*The Maury Island incident <p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">A Ufologist who disagrees that the Ed Walters Gulf Breeze photos are hoaxes is naval optical physicist Bruce Maccabee. He investigated the incident, analyzed the various photos and deemed them authentic.<sup class="reference" id="cite_ref-91" style="line-height: 1em; font-weight: normal; font-style: normal; ">[92] Maccabee claimed he himself was among independent witnesses of some of the Gulf Breeze sightings.<sup class="reference" id="cite_ref-92" style="line-height: 1em; font-weight: normal; font-style: normal; ">[93]
 * The Ummo affair, a decades-long series of detailed letters and documents allegedly from extraterrestrials. The total length of the documents is at least 1000 pages, and some estimate that further undiscovered documents may total nearly 4000 pages. A José Luis Jordan Pena came forward in the early nineties claiming responsibility for the phenomenon, and most<sup class="noprint Inline-Template" style="line-height: 1em; white-space: nowrap; " title="The material in the vicinity of this tag may use weasel words or too-vague attribution. from December 2008">[who?] consider there to be little reason to challenge his claims.<sup class="reference" id="cite_ref-89" style="line-height: 1em; font-weight: normal; font-style: normal; ">[90]
 * George Adamski over the space of two decades made various claims about his meetings with telepathic aliens from nearby planets. He claimed that photographs of the far side of the moon taken by a Soviet orbital probe in 1959 were fake, and that there were cities, trees and snow-capped mountains on the far side of the moon. Among copycats was a shadowy British figure named Cedric Allingham.
 * In 1987/88, Ed Walters allegedly perpetrated a hoax in Gulf Breeze, Florida. Walters claimed at first having seen a small UFO flying near his home, and then in a second incident seeing the same UFO and a small alien being standing by his back door after being alerted by his dog. Several photographs were taken of the craft, but none of the being. Three years later, in 1990, after the Walters family had moved, the new residents discovered a model of a UFO poorly hidden in the attic that bore an undeniable resemblance to the craft in Walters' photographs. Various witnesses and detractors came forward after the local Pensacola newspaper printed a story about the discovered model, and some investigators<sup class="noprint Inline-Template" style="line-height: 1em; white-space: nowrap; " title="The material in the vicinity of this tag may use weasel words or too-vague attribution. from December 2008">[who?] now consider the sightings to be a hoax. In addition, a six-figure television miniseries and book deal were nearly struck with Walters.
 * Warren William "Billy" Smith is a popular writer and confessed hoaxster.<sup class="reference" id="cite_ref-90" style="line-height: 1em; font-weight: normal; font-style: normal; ">[91]

In popular culture
Main article: UFOs in fiction<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">UFOs constitute a widespread international cultural phenomenon of the last 60 years. Gallup polls rank UFOs near the top of lists for subjects of widespread recognition. In 1973, a survey found that 95 percent of the public reported having heard of UFOs, whereas only 92 percent had heard of U.S. President Gerald Ford in a 1977 poll taken just nine months after he left the White House.<sup class="reference" id="cite_ref-93" style="line-height: 1em; font-weight: normal; font-style: normal; ">[94] A 1996 Gallup pollreported that 71 percent of the United States population believed that the government was covering up information regarding UFOs. A 2002Roper poll for the Sci Fi Channel found similar results, but with more people believing that UFOs are extraterrestrial craft. In that latest poll, 56 percent thought UFOs were real craft and 48 percent that aliens had visited the Earth. Again, about 70 percent felt the government was not sharing everything it knew about UFOs or extraterrestrial life.<sup class="reference" id="cite_ref-94" style="line-height: 1em; font-weight: normal; font-style: normal; ">[95] <sup class="reference" id="cite_ref-95" style="line-height: 1em; font-weight: normal; font-style: normal; ">[96] <sup class="reference" id="cite_ref-96" style="line-height: 1em; font-weight: normal; font-style: normal; ">[97] Another effect of the flying saucer type of UFO sightings has been Earth-made flying saucer craft in space fiction, for example the Earth spacecraft Starship C-57D in Forbidden Planet, the Jupiter Twoin Lost in Space, and the saucer section of the USS Enterprise in Star Trek, and many others. For an excellent analysis of the interrelationship between popular culture and UFOs consult the research by psychologist Armando Simon, especially his contribution in Richard Haines' book, UFO Phenomena and the Behavioral Scientist.