UFOs are unidentified flying objects.

UFOs are any real or apparent flying object which cannot be identified by the observer and which remains unidentified after investigation. UFOS are also called unidentified flying objects. UFOs doesn't specially mean an alien craft. UFOs merely means the object has not been identified.

A purported 1952 photo of UFOs over Passaic, New Jersey, from an FBI document.

Sightings of UFOs date back to ancient times. However, reports of UFOs started to become more common after the first widely publicized U.S. sighting in 1947. Many tens of thousands of such claimed observations have since been reported worldwide. It is very likely many more go unreported due to fear of public ridicule because of the social stigma created around the UFO topic.

In popular culture throughout the world, UFO is commonly used to refer to any hypothetical alien spacecraft but the term flying saucer is also regularly used. Once a UFO is identified as a known object (for example an aircraft or weather balloon), it ceases to be a UFO and becomes an identified object. In such cases, it is inaccurate to continue to use the acronym UFO to describe the object.

History of UFOs.

Unusual aerial phenomena have been reported throughout history. Some of these strange apparitions may have been astronomical phenomena such as comets or bright meteors, or atmospheric optical phenomena such as parhelia and the rare, yet understood, lenticular clouds. Examples of these reports include:

• During the reign of pharaoh Thutmose III around 1450 BC, there is a description of multiple "circles of fire" brighter than the Sun and about 5 metres in size that appeared over multiple days. They finally disappeared after ascending higher in the sky.

• The Roman author Julius Obsequens writes that in 99 BC, "in Tarquinia towards sunset, a round object, like a globe, a round or circular shield, took its path in the sky from west to east.".

• On September 24, 1235, General Yoritsume and his army observed unidentified globes of light flying in erratic patterns in the night sky near Kyoto, Japan. The general’s advisers told him not to worry -- it was merely the wind causing the stars to sway.

UFOs 1566 woodcut by Hans Glaser of 1561 Nuremberg event.

• On April 14, 1561 the skies over Nuremberg, Germany were reportedly filled with a multitude of objects seemingly engaged in an aerial battle. Small spheres and discs were said to emerge from large cylinders. (image right).

These sightings were usually treated as supernatural portents, angels, and other religious omens. Some contemporary investigators believe them to be the ancient equivalent of modern UFO reports.

First modern reports of UFOs.

Before the terms "flying saucer" and "UFO" were coined, there were a number of reports of strange, unidentified aerial phenomena. These reports date from the mid-nineteenth to early twentieth century. They include:

Purported photo of a UFO over New Hampshire in 1870.

• On July, 1868, The investigators of this phenomenon define the first modern documented sighting as having happened in Copiapo city, Chile.

• 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.".

• On November 17, 1882, Astronomer E. W. Maunder of the Greenwich Royal Observatory described in the Observatory Reports "a strange celestial visitor" that was "disc-shaped," "torpedo-shaped," or "spindle-shaped." It was said to be very different in characteristics from a meteor fireball. Years later, Maunder wrote it looked exactly like the new Zeppelin dirigibles. The strange object was also seen by several other European astronomers.

• On February 28, 1904, there was a sighting by three crew members on the USS Supply 300 miles west of San Francisco, reported by Lt. Frank Schofield, later to become Commander-in-Chief of the Pacific 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 2 to 3 minutes. The largest had an apparent size of about six suns.

• The so-called Fátima incident or "The Miracle of the Sun," witnessed by tens of thousands in Fátima, Portugal on October 13, 1917, is believed by some researchers to actually be a UFO event.

• On August 5, 1926, while travelling in the Humboldt Mountains of Tibet's Kokonor region, Nicholas Roerich reported that members of his expedition saw--high in the sky, above an eagle they had been watching--"something big and shiny reflecting sun, like a huge oval moving at great speed" (from his travel diary Altai-Himalaya, published 1929). While Roerich does not say what he thought the object might have been, surrounding passages discuss Theosophical accounts of ancient civilizations and their technology..

• In both the European and Japanese aerial theatres during World War II, "Foo-fighters" (balls of light and other shapes that followed aircraft) were reported by both Allied and Axis pilots.

• On February 25, 1942, an unidentified craft was detected over the California region. The craft stayed aloft despite taking at least 20 minutes worth of flak from ground batteries. The incident later became known as the Battle of Los Angeles, or the West coast air raid.

• In 1946, there were over 2000 reports of unidentified aircraft 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 Russian tests of captured German V1 or V2 rockets. This was subsequently shown not to be the case, and the phenomenon remains unexplained. Over 200 were tracked on radar and deemed to be "real physical objects" by the Swedish military. A significant fraction of the remainder were thought to be misidentification of natural phenomena, such as meteors.

Canadian investigation.

The Falcon Lake incident report filed by the Royal Canadian Mounted Police on Stephen Michalak claimed incident with a UFO.

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 the Shag Harbour incident in Nova Scotia. [47] 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.

4. Famous Canadian cases

In the Shag Harbour incident, a large object sequentially flashing lights was seen and heard to dive into the water by multiple witnesses. The Royal 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.

Modern UFO era.

The post World War II UFO phase in the United States began with a reported sighting by American businessman Kenneth Arnold on June 24, 1947 while flying his private plane near Mount Rainier, Washington. He reported seeing nine brilliantly bright objects flying across the face of Rainier towards nearby Mount Adams at "an incredible speed", which he calculated at at least 1200 miles per hour by timing their travel between Rainier and Adams. His sighting subsequently received significant media and public attention. Arnold would later say they "flew like a saucer would if you skipped it across the water" and also said they were "flat like a pie pan", "shaped like saucers," and "half-moon shaped, oval in front and convex in the rear. ...they looked like a big flat disk." (One, however, he would describe later as being almost crescent-shaped.) Arnold’s reported descriptions caught the media’s and the public’s fancy and gave rise to the terms flying saucer and flying disk.

Arnold’s sighting was followed in the next few weeks by several thousand other reported sightings, mostly in the U.S., but in other countries as well. Perhaps the most significant of these was a United Airlines crew sighting of nine more disc-like objects over Idaho on the evening of July 4. This sighting was even more widely reported than Arnold’s and lent considerable credence to Arnold’s report. For the next few days most American newspapers were filled with front-page stories of the new "flying saucers" or "flying discs." Starting with official debunkery that began the night of 8 July with the Roswell UFO incident, reports rapidly tapered off, ending the first big U.S. UFO wave.

Starting July 9, Army Air Force intelligence, in cooperation with the FBI, secretly began a formal investigation into the best sightings, which included Arnold’s and the United crew’s. The FBI was told that intelligence was using "all of its scientists" to determine whether or not "such a phenomenon could, in fact, occur." Furthermore, 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." (Maccabee, 5) Three weeks later they concluded that, "This 'flying saucer’ situation is not all imaginary or seeing too much in some natural phenomenon. Something is really flying around." 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 either manual, automatic, or remote control. It was thus recommended in late September 1947 that an official Air Force investigation be set up to investigate the phenomenon. This led to the creation of the Air Force’s Project Sign at the end of 1947, which became Project Grudge at the end of 1948, and then Project Blue Book in 1952. Blue Book closed down in 1970, ending the official Air Force UFO investigations.

A claimed UFO from Brazil. The circular aura suggests it is a light in the foreground.

Use of "UFO" instead of "flying saucer" was first suggested in 1952 by Capt. Edward J. Ruppelt, the first director of Project Blue Book, who felt that "flying saucer" did not reflect the diversity of the sightings. Ruppelt suggested that "UFO" should be pronounced as a word - "you-foe". However it is generally pronounced by forming each letter: "U.F.O." His term was quickly adopted by the Air Force, which also briefly used "UFOB" circa 1954. (See next paragraph.) Ruppelt recounted his experiences with Project Blue Book in his memoir, The Report on Unidentified Flying Objects (1956), also the first book to use the term.

Air Force Regulation 200-2, issued in 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." Furthermore, Air Force personnel were directed not to discuss unexplained cases with the press.

UFOs in popular culture

Beginning in the 1950s, UFO-related spiritual sects, sometimes referred to as contactee cults, began to appear. Most often the members of these sects rallied around a central individual, who claimed to either have made personal contact with space-beings, or claimed to be in telepathic contact with them. Prominent among such individuals was George Adamski, who claimed to have met a tall, blond-haired Venusian named "Orthon," who came to warn us about the dangers of nuclear proliferation. Adamski was widely dismissed, but an Adamski Foundation still exists, publishing and selling Adamski’s writings. At least two of these sects developed a substantial number of adherents, most notably The Aetherius Society, founded by British mystic George King in 1956, and the Unarius Foundation, established by "Ernest L." and Ruth Norman in 1954. A standard theme of the alleged messages from outer-space beings to these cults was a warning about the dangers of nuclear proliferation. More recent groups organized around an extraterrestrial theme include Ummo, Heaven’s Gate, Raël, and the Ashtar Galactic Command. Many of the early UFO sects, as well as later ones, share a tendency to incorporate ideas from both Christianity and various eastern religions, "hybridizing" these with ideas pertaining to extraterrestrials and their benevolent concern with the people of Earth.

The notion of contactee cults gained a new twist during the 1980s, primarily in the USA, with the publication of books by Whitley Strieber (beginning with Communion) and Jacques Vallee (Passport to Magonia). Strieber, a horror writer, felt that aliens were harassing him and were responsible for "missing time" during which he was subjected to strange experiments by "grey aliens". This newer, darker model can be seen in the subsequent wave of "alien abduction" literature, and in the background mythos of The X Files and many other TV series.

However, even in the alien abduction literature, motives of the aliens run the gamut from hostile to benevolent. For example, researcher David Jacobs believes we are undergoing a form of stealth invasion through genetic assimilation. The theme of genetic manipulation (though not necessarily an invasion) is also strongly reflected in the writings of Budd Hopkins. The late Harvard psychiatrist John Mack (1929-2004) believed that the aliens’ ethical bearing was to take a role as "tough love" gurus trying to impart wisdom. James Harder says abductees predominantly report positive interactions with aliens, most of whom have benevolent intentions and express concern about human survival.

An interesting 1970s-era development was a renewal and broadening of ideas associating UFOs with supernatural or preternatural subjects such as occultism, cryptozoology, and parapsychology. Some 1950s contactee cultists had incorporated various religious and occult ideas into their beliefs about UFOs, but in the 1970s this was repeated on a considerably larger scale. Many participants in the New Age movement came to believe in alien contact, both through mediumistic channeling and through literal, physical contact. A prominent spokesperson for this trend was actress Shirley MacLaine, especially in her book and miniseries, Out On a Limb. The 1970s saw the publication of many New Age books in which ideas about UFOs and extraterrestrials figured prominently.

Another key development in 1970s UFO folklore came with the publication of Erich von Däniken’s book Chariots of the Gods. The book argued that aliens have been visiting Earth for thousands of years, which he used to explain UFO-like images from various archaeological sources as well as unsolved mysteries. Such ideas were not exactly new. For example, earlier in his career, astronomer Carl Sagan in Intelligent Life in the Universe (1966) had similarly argued that aliens could have been visiting the Earth sporadically for millions of years. "Ancient astronauts" proposals inspired numerous imitators, sequels, and fictional adaptations, including one book (Barry Downing's The Bible and Flying Saucers) which interprets miraculous aerial phenomena in the Bible as records of alien contact. Many of these interpretations posit that aliens have been guiding Human evolution, an idea taken up earlier by the novel and film 2001: A Space Odyssey.

UFOs constitute a widespread international cultural phenomenon of the last half-century. Folklorist Thomas E. Bullard writes, "UFOs have invaded modern consciousness in overwhelming force, and endless streams of books, magazine articles, tabloid covers, movies, TV shows, cartoons, advertisements, greeting cards, toys, T-shirts, even alien-head salt and pepper shakers, attest to the popularity of this phenomenon." 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 US President Gerald Ford in a 1977 poll taken just nine months after he left the White House. (Bullard, 141) A 1996 Gallup poll reported that 71 percent of the United States population believed that the government was covering up information regarding UFOs. A 2002 Roper poll for the Sci Fi channel found similar results, but with more people believing UFOs were 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.

Research into UFOs.

ufology is a Neologism coined to describe the collective efforts of those who study UFO reports and associated evidence. While ufology does not represent an academic research program, UFOs have been subject to various investigations over the years, varying widely in scope and scientific rigor. Governments or independent academics in the United States, Canada, the United Kingdom, France, Belgium, Sweden, Brazil, Mexico, Spain, and the Soviet Union are known to have investigated UFO reports at various times. No national government has ever publicly suggested that UFOs represent any form of alien intelligence. Perhaps the best known study was Project Blue Book, previously Project Sign and Project Grudge, conducted by the United States Air Force from 1947 until 1969. Other notable investigations include the Robertson Panel (1953), the Brookings Report (1960), the Condon Committee (1966-1968), the Green Fireballs/Project Twinkle investigation (1948-1951), the Sturrock Panel (1998), and the French GEPAN/SEPRA (1977-2004) and COMETA (1996-1999) study groups.

UFO categorization.

Some researchers 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).
• Rapidly-moving lights or lights with apparent ability to rapidly change direction".
• Large triangular "craft" or triangular light pattern.
• Cigar-shaped "craft" with lighted windows (Meteor fireballs are sometimes reported this way, but are a very different phenomema).
• Other: chevrons, equilateral triangles, spheres (usually reported to be shining, glowing at night), domes, diamonds, shapeless black masses, eggs, and cylinders.

Hynek system of identifying UFOs.

Dr. J. Allen Hynek developed another commonly used system of description, dividing sightings into six categories. It first separates sightings on the basis of proximity, arbitrarily using 500 feet as the cutoff point. It then subdivides these into divisions based on viewing conditions or special features. The three distant sighting categories are:

• Nocturnal Lights (NL): Anomalous lights seen in the night sky.
• Daylight Discs (DD): Any anomalous object, generally but not necessarily "discoidal", seen in the distant daytime sky.
• Radar/Visual cases (RV). Objects seen simultaneously by eye and on radar.

The distant classification is useful in terms of evidentiary value, with RV cases usually considered to be the highest because of radar corroboration and NL cases the lowest because of the ease in which lights seen at night are often confused with prosaic phenomena such as meteors, bright stars, or airplanes. RV reports are also fewest in number, while NL are largest.

In addition were three "close encounter" (CE) subcategories, again thought to be higher in evidentiary value, because it includes measurable physical effects and the objects seen up close are less likely to be the result of misperception. As in RV cases, these tend to be relatively rare:

• CE1: Strange objects seen nearby but without physical interaction with the environment.
• CE2: A CE1 case but creating physical evidence or causing electromagnetic interference (see below).
• CE3: CE1 or CE2 cases where "occupants" or entities are seen. (Hence the title of Steven Spielberg's movie, Close Encounters of the Third Kind).

Hynek's CE classification system has since been expanded to include such things as alleged alien abductions and cattle mutilation phenomena.

Vallee System of UFO identification.

Jacques Vallee has devised a UFO classification system which is preferred by many UFO investigators over Hynek's system as it is considerably more descriptive than Hynek's, especially in terms of the reported behavior of UFOs.

Type - I (a, b, c, d)- Observation of an unusual object, spherical discoidal, or of another geometry, on or situated close to the ground (tree height, or lower), which may be associated with traces - thermal, luminous, or mechanical effects.

• a - On or near ground.
• b - Near or over body of water.
• c - Occupants appear to display interest in witnesses by gestures or luminous signals.
• d - Object appears to be "scouting" a terrestrial vehicle.

Type - II (a, b, c) - Observation of an unusual object with vertical cylindrical formation in the sky, associated with a diffuse cloud. This phenomenon has been given various names such as "cloud-cigar" or "cloud-sphere."

• a - Moving erratically through the sky.
• b - Object is stationary and gives rise to secondary objects (sometimes referred to as "satellite objects").
• c - Object is surrounded by secondary objects.

Type - III (a, b, c, d, e)- Observation of an unusual object of spherical, discoidal or elliptical shape, stationary in the sky.

• a - Hovering between two periods of motion with "falling-leaf" descent, up and down, or pendulum motion.
• b - Interruption of continuous flight to hover and then continue motion.
• c - Alters appearance while hovering - e.g., change of luminosity, generation of secondary object, etc.
• d - "Dogfights" or swarming among several objects.
• e - Trajectory abruptly altered during continuous flight to fly slowly above a certain area, circle, or suddenly change course.

Type IV (a, b, c, d) - Observation of an unusual object in continuous flight.

• a - Continuous flight.
• b - Trajectory affected by nearby conventional aircraft.
• c - Formation flight.
• d - Wavy or zig-zag trajectory.

Type V (a, b, c)- Observation of an unusual object of indistinct appearance, i.e., appearing to be not fully material or solid in structure.

• a - Extended apparent diameter, non-point source luminous objects ("fuzzy").
• b - Starlike objects (point source), motionless for extended periods.
• c - Starlike objects rapidly crossing the sky, possibly with peculiar trajectories.

Source: 1. Jacques and Janine Vallee: Challenge To Science: The UFO Enigma, LC# 66-25843

Physical evidence of UFOs.

Fata 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.

Besides visual sightings, cases sometimes have alleged associated direct or indirect physical evidence, including many cases studied by the military and various government agencies of different countries. Indirect physical evidence would be data obtained from afar, such as radar contact and photographs. More direct physical evidence involves physical interactions with the environment at close range-Hynek's "close encounter" or Vallee's "Type-I" cases-which include "landing traces," electromagnetic interference, and physiological/biological effects.

A list of various physical evidence cases from government and private studies includes:

• radar contact and tracking, sometimes from multiple sites. These are often considered among the best cases since they usually involve trained 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 multiple NATO radar and jet interceptors, and investigated by Belgium's military (included photographic evidence). Another famous case from 1986 was the JAL 1628 case over Alaska investigated by the FAA.
• Photograpic evidence, including still photos, movie film, and video, including some in the Infrared spectrum (rare).
• Recorded visual spectrograms (extremely rare).
• Recorded gravimetric and magnetic disturbances (extremely rare).
• Landing physical trace evidence, including ground impressions, burned and/or desiccated soil, burned and broken foliage, magnetic anomalies, increased radiation levels, and metallic traces. See, e.g. Height 611 UFO Incident or the 1964 Lonnie Zamora's Socorro, New Mexico encounter, considered one of the most inexplicable of the USAF Project Blue Book cases). A well-known example from December 1980 was the USAF Rendlesham Forest Incident in England. Another less than 2 weeks later, in January 1981, occurred in Trans-en-Provence and was investigated by GEPAN, 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. Catalogs of several thousand such cases have been compiled, particularly by researcher Ted Phillips.
• Physiological effects on people and animals including temporary paralysis, skin burns and rashes, corneal burns, and symptoms resembling Radiation poisoning, such as the Cash-Landrum incident in 1980. One such case dates back to 1886, a Venezuelan incident reported in Scientific American magazine.
• So-called Animal/Cattle Mutilation cases, that some feel are also part of the UFO phenomenon. Such cases can and have been analyzed using forensic science techniques.
• 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, including stalled cars, power black-outs, radio/TV interference, magnetic compass deflections, and aircraft navigation, communication, and engine disruption. A list of over 30 such aircraft EM incidents was compiled by NASA scientist Dr. Richard F. Haines. A famous 1976 military case over Tehran, recorded in CIA and DIA classified documents, resulted in communication losses in multiple aircraft and weapons system failure in an F-4 jet interceptor as it was about to fire a missile on one of the UFOs. This was also a radar/visual case. (Fawcett & Greenwood, 81-89; Good, 318-322, 497-502).
• 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.
• Actual hard physical evidence cases, 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.
• Misc: Recorded electromagnetic emissions, such as microwaves detected in the well-known 1957 RB-47 surveillance aircraft case, which was also a visual and radar case; polarization rings observed around a UFO by a scientist, explained by Dr. James Harder as intense magnetic fields from the UFO causing the Faraday effect.

These various reported physical evidence cases have been studied by various scientist and engineers, both privately and in official governmental studies (such as Project Blue Book, the Condon Committee, and the French GEPAN/SEPRA). A comprehensive scientific review of physical evidence cases was carried out by the 1998 Sturrock UFO panel.

Attempts have been made to reverse engineer the possible physics behind UFOs through analysis of both eyewitness reports and the physical evidence. Examples are former NASA and nuclear engineer James McCampbell in his book Ufology online, 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 of a microwave plasma parting the air in front of the craft is currently being researched by Dr. Leik Myrabo, Professor of Engineering Physics at the Rensselaer Polytechnic Institute as a possible advance in hypersonic flight. 1995 Aviation Week article

Notable UFO-related sightings and events

In January 2007, the French Centre National d'Études Spatiales (CNES) declared it will publish an archive of UFO sightings and other phenomena online.

• List of major UFO sightings.
• Australian UFO Sightings.

Explanations and opinions of UFOs.

Statistics compiled by U.S. Air Force studies from 1947-1970 found that the strong preponderance of identified sightings were due to misidentifications, with hoaxes and psychological aberrations accounting for only a few percent of all cases.

Nevertheless, many cases remained unexplained. An Air Force study by Battelle Memorial Institute scientists from 1952-1955 of 3200 USAF cases found 22% were unknowns, and with the best cases, 33% remained unsolved. Similarly about 30% of the UFO cases studied by the 1969 USAF Condon Committee were deemed unsolved when reviewed by the American Institute of Aeronautics and Astronautics (AIAA). The official French government UFO scientific study (GEPAN/SEPRA) from 1976 to 2004 listed about 13% of 5800 cases as very detailed yet still inexplicable (with 46% deemed to have definite or probable explanations and 41% having inadequate information).

Despite the remaining unexplained cases in the cited scientific studies above, many skeptics still argue that the general opinion of the mainstream scientific community is that all UFO sightings could ultimately be explained by prosaic explanations such as misidentification of natural and man-made phenomena (either known or still unknown), hoaxes, and psychological phenomena such as optical illusions or dreaming/sleep paralysis (often given as an explanation for purported alien abductions)

Other skeptical arguments against UFOs include:

• Most evidence is ultimately derived from notoriously unreliable eyewitness accounts and very little in the way of solid or other physical evidence has been reported.
• Most UFO sightings are transitory events and there is usually no opportunity for the repeat testing called for by the scientific method.
• Occam's razor of hypothesis testing, since it is considered less incredible for the explanations to be the result of known scientifically verified phenomena rather than resulting from novel mechanisms (e.g. the extraterrestrial hypothesis).
• The market being biased in favour of books, TV specials, etc. which support paranormal interpretations, leaving the public poorly informed regarding more mundane explanations for UFOs as a possibly socio-cultural phenomenon only.

Popular ideas for explaining UFOs.

To account for hardcore unsolved cases, a number of explanations have been proposed by both proponents and skeptics. Among proponents, some of the more common explanations for UFOs are:

• The Extraterrestrial Visitation Hypothesis (ETH) (most popular).
• The Interdimensional Hypothesis.
• The Paranormal/Occult Hypothesis.
• The hypothesis that they are time machines or vehicles built in a future time.

Similarly, skeptics usually propose the following explanations:

• The Psychological-Social Hypothesis.
• The man-made craft hypothesis (see Military flying saucers).
• The unknown natural phenomena hypothesis, e.g. ball lightning, sprites.
• The Earthlights/Tectonic Strain hypothesis.

Usually a combination of explanations is cited to explain all cases, and even proponents will sometimes invoke skeptical explanations, such as man-made craft, to possibly account for some unsolved cases.

Identified flying objects (IFOs).

Lenticular clouds have been reported as UFOs due to their peculiar shape.

It has been estimated from various studies that 50-90% of all reported UFO sightings are eventually identified, while typically 10-20% remain unidentified. Studies also show only a tiny percentage of UFO reports to be deliberate hoaxes; most are honest misidentifications of natural and man-made phenomena.

Generally studies indicate that misidentifications fall into three basic categories: astronomical causes (planets, stars, meteors, etc.), aircraft, and balloons. These typically account for 80-90% of the IFOs, with all other causes (such as birds, clouds, mirages, searchlights, etc.) being rare and accounting for the remainder.

The actual percentages of IFOs vs. UFOs depends on who is doing the study and can vary widely depending on the used database, evaluation criteria, personal biases, and politics. Results can also fluctuate from year to year. For details, see Identified flying objects

UFOs: the hoaxes.

Among the many people who have reported UFO sightings, some have been exposed as hoaxers. Not all alleged hoax exposures are certain, however, and many claimants have stuck by their stories, leaving the determination of specific cases as hoaxes contentious. Some of the controversial subjects include these:

• Contactees such as George Adamski, who claimed he went on flights in UFOs. (Some believers even contend he had real experiences and later fictionalized others, leaving the subject murky.).
• Billy Meier, some of whose photographs have been discredited.
• Ed Walters of the Gulf Breeze, Florida UFO reports.
• Documents surrounding Majestic 12, a purportedly super-secret high-level United States UFO information management group formed during the Truman administration.
• The Maury Island Incident.
• Bob Lazar, who claimed to have been hired to help reverse engineer saucer craft at Area 51.
• The Ummo affair, a series of detailed letters and documents allegedly from extraterrestrials.
• An online list of reportedly Discredited Sightings.
• The sci-fi channel ran an advertising promo of a UFO near the World Trade Center being seen by a group of tourists in a helicopter. Since then photos of a UFO near the towers during the September 11, 2001 attacks have been cropping up all over the net. Some also are using this supposed sighting as conspiracy theory evidence of a deliberate missile attack.

UFOs in psychology.

The study of UFO claims over the years has led to valuable discoveries about atmospheric phenomena and psychology. In psychology, the study of UFO sightings has revealed information on misinterpretation, perceptual illusions, hallucination and fantasy-prone personality, which may explain why some people are willing to believe hoaxers such as George Adamski. Many have questioned the reliability of hypnosis in UFO abduction cases.

Astronomers and other scientists view of UFOs.

Although it is sometimes contended that Astronomers never report UFOs, the Air Force's Project Blue Book files indicate that approximately 1% of all their reports came from amateur and professional astronomers or other users of telescopes (such as missile trackers or surveyors). In the 1970s, astrophysicist Peter A. Sturrock conducted two surveys of the American Institute of Aeronautics and Astronautics and American Astronomical Society. About 5% of the members polled indicated that they had had UFO sightings. In 1980, a survey of 1800 members of various amateur astronomer associations by Gert Helb and astronomer J. Allen Hynek of 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?"

Astronomer Clyde Tombaugh, who admitted to 6 UFO sightings, including 3 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 Dr. Lincoln La Paz, who had headed the Air Force's investigation into the Green Fireballs and other UFO phenomena in New Mexico. La Paz reported 2 personal sightings, one of a green fireball, the other of an anomalous disc-like object. Even later UFO debunker Dr. Donald Menzel filed a UFO report in 1949.

Various public scientific studies have over the past half century have examined UFO reports in great detail. None of these studies have officially concluded that any reports are caused by extraterrestrial spacecraft (e.g., Seeds 1995:A4). Some studies were 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. Other private or governmental studies, some secret, have concluded in favor of the ETH, or have had members who disagreed with the official conclusions. The following are examples of such studies and individuals:

• One of the earliest government studies to come to a secret ETH conclusion was Project Sign, the first official Air Force UFO investigation. In 1948, they wrote a top-secret intelligence estimate to that effect. The Air Force Chief of Staff ordered it destroyed. The existence of this suppressed report was revealed by several insiders who had read it, such as astronomer and USAF consultant Dr. J. Allen Hynek and Edward J. Ruppelt, the first head of the USAF's Project Blue Book. (Ruppelt, Chapt. 3).
• An early U.S. Army study, of which little is known, was called the Interplanetary Phenomenon Unit (IPU). 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 1950's 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. (Good, 484).
• In 1967, Greek physicist Paul Santorini, a Manhattan project scientist, publicly stated that a 1947 Greek government investigation that he headed into the European ghost rockets of 1946 quickly came to the conclusion that they were not missiles. Santorini claimed the investigation was then squashed by military officials from the U.S., who knew them to be extraterrestrial, because there was no defense against the advanced technology and they feared widespread panic should the results become public. (Good, 23).
• Various European countries conducted a secret joint study in 1954, also concluding that UFOs were extraterrestrial. This study was revealed by German rocketry pioneer Hermann Oberth, a member of the study, who also made many public statements supporting the ETH.
• During the height of the flying saucer epidemic of July 1952, including highly publicized radar/visual and jet intercepts over Washington D.C., the FBI was informed by the Air Force Directorate of Intelligence that they thought the "flying saucers" were either "optical illusions or atmospheric phenomena" but then added that, "some Military officials are seriously considering the possibility of interplanetary ships." FBI document.
• The CIA started their own internal scientific review the following day. Some CIA scientists were also seriously considering the ETH. An early memo from August was very skeptical, but also added, "...as long as a series of reports remains 'unexplainable' (interplanetary aspects and alien origin not being thoroughly excluded from consideration) caution requires that intelligence continue coverage of the subject." A report from later that month was similarly skeptical but nevertheless concluded "...sightings of UFOs reported at Los Alamos and Oak Ridge, at a time when the background radiation count had risen inexplicably. Here we run out of even 'blue yonder' explanations that might be tenable, and we still are left with numbers of incredible reports from credible observers." A December 1952 memo from the Assistant CIA Director of Scientific Intelligence (O/SI) was much more urgent: "...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 travelling at highs speeds in the vicinity of U.S. defense installation are of such nature that they are not attributable to natural phenomena or known types of aerial vehicles." Some of the memos also made it clear that CIA interest in the subject was not to be made public, partly in fear of possible public panic. (Good,331-335).
• The CIA organized the January 1953 Robertson Panel of scientists to debunk the data collected by the Air Force's Project Blue Book. This included an engineering analysis of UFO maneuvers by Blue Book (including a motion picture film analysis by Naval scientists) that had concluded UFOs were under intelligent control and likely extraterrestrial. (Dolan, 189; Good, 287, 337; Ruppelt, Chapt. 16)).
• Extraterrestrial "believers" within Project Blue Book including Major Dewey Fournet, in charge of the engineering analysis of UFO motion. Director Edward J. Ruppelt is also thought to have held these views, though expressed in private, not public. Another defector from the official Air Force party line was consultant Dr. J. Allen Hynek, who started out as a staunch skeptic. After 20 years of investigation, he changed positions and generally supported the ETH. He became the most publicly known UFO advocate scientist in the 1970s and 1980s.
• The first CIA Director, Vice Admiral Roscoe H. Hillenkoetter, stated in a signed statement to Congress, also reported in the New York Times, February 28, 1960, that, "It is time for the truth to be brought out... Behind the scenes high-ranking Air Force officers are soberly concerned about the UFOs. But through official secrecy and ridicule, many citizens are led to believe the unknown flying objects are nonsense.... I urge immediate Congressional action to reduce the dangers from secrecy about unidentified flying objects." In 1962, in his letter of resignation from NICAP, he told director Donald Keyhoe, "I know the UFOs are not U.S. or Soviet devices. All we can do now is wait for some actions by the UFOs." (Good, 347).
• Although the 1968 Condon Report came to a negative conclusion (written by Condon), it is known that many members of the study strongly disagreed with Condon's methods and biases. Most quit the project in disgust or were fired for insubordination. A few became ETH supporters. Perhaps the best known example is Dr. David Saunders, who in his 1968 book UFOs? Yes lambasted Condon for extreme bias and ignoring or misrepresenting critical evidence. Saunders wrote, "It is clear... that the sightings have been going on for too long to explain in terms of straightforward terrestrial intelligence. It is in this sense that ETI (Extra Terrestrial Intelligence) stands as the `least implausible' explanation of `real UFOs'.".
• Nick Pope, the head of the UK government UFO desk for a number of years, is an advocate of the ETH based on the inexplicable cases he reviewed, such as the Rendlesham UFO incident, although the British government has never made such claims.
• Jean-Jacques Velasco, the head of the official French UFO investigation SEPRA, wrote a book in 2005 saying that 14% of the 5800 cases studied by SEPRA were utterly inexplicable and extraterrestrial in origin. Yves Sillard, the head of the new official French UFO investigation GEIPAN and former head of the French space agency CNES, echos Velasco's comments and adds the U.S. is guilty of covering up this information. Again, this isn't the official public posture of SEPRA, CNES, or the French government. (CNES recently announced that their 5800 case files will be placed on the Internet starting March 2007.).
• The 1999 French COMETA committee of high-level military analysts/generals and aerospace engineers/scientists declared the ETH was the best hypothesis for the unexplained cases.

UFOs the conspiracy theories.

UFOs are sometimes an element of elaborate conspiracy theories in which the government is said to be 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.

Probably most ufologists believe the basic premise that various world governments are covering up UFO information. In the U.S., opinion polls again indicate that a strong majority of people believe the U.S. government is witholding such information. 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).

There is also speculation that UFO phenomena are tests of experimental aircraft or advanced weapons. In this case UFOs are viewed as failures to retain secrecy, or deliberate attempts at disinformation: to deride the phenomenon so that it can be pursued unhindered. This explanation may or may not feed back into the previous one, where current advanced military technology is considered to be adapted alien technology. (See also: skunk works and Area 51)

It has also been suggested by a few fringe authors that all or most human technology and culture is based on extraterrestrial contact. See also Ancient astronauts.

Allegations of evidence suppression on UFOs.

Some also contend regarding physical evidence that it exists abundantly but is swiftly and sometimes clumsily suppressed by governments, aiming to insulate a population they regard as unprepared for the social, theological, and security implications of such evidence. See the Brookings Report.

There have been allegations of suppression of UFO related evidence for many decades. (See also Men in Black) Some examples are:

• On July 7, 1947, William Rhodes took photos of an unusual object over Phoenix, Arizona. The photos appeared in a Phoenix newspaper and a few other papers. According to documents from Project Bluebook, an Army counter-intelligence (CIC) agent and an FBI agent interviewed Rhodes on August 29 and convinced him to surrender the negatives. The CIC agent deliberately concealed his true identity, leaving Rhodes to believe both men were from the FBI. Rhodes said he wanted the negatives back, but when he turned them into the FBI the next day, he was informed he wouldn't be getting them back, though Rhodes later tried unsuccessfully. The photos were extensively analyzed and would eventually show up in some classified Air Force UFO intelligence reports. (Randle, 34-45, full account).
• A June 27, 1950, movie of a "flying disk" over Louisville, Kentucky, taken by a Louisville Courier-Journal photographer, had the USAF Directors of counterintelligence (AFOSI) and intelligence discussing in memos how to best obtain the movie and interview the photographer without revealing Air Force interest. One memo suggested the FBI be used, then precluded the FBI getting involved. Another memo said "it would be nice if OSI could arrange to secure a copy of the film in some covert manner," but if that wasn't feasible, one of the Air Force scientists might have to negotiate directly with the newspaper. In a recent interview, the photographer confirmed meeting with military intelligence and still having the film in his possession until then, but refused to say what happened to the film after that.
• In another 1950 movie incident from Montana, Nicholas Mariana filmed some unusual aerial objects and eventually turned the film over to the U.S. Air Force, but insisted that the first part of the film, clearly showing the objects as spinning discs, had been removed when it was returned to him. (Clark, 398).
• During the military investigation of Green Fireballs in New Mexico, UFOs were photographed by a tracking camera over White Sands Proving Grounds on April 27, 1949. The final report in 1951 on the green fireball investigation claimed there was insufficient data to determine anything. But documents later uncovered by Dr. Bruce Maccabee indicate that triangulation was accomplished. The data reduction and photographs showed four objects about 30 feet in diameter flying in formation at high speed at an altitude of about 30 miles. Maccabee says this result was apparently suppressed from the final report.
• Project Blue Book director Edward J. Ruppelt reported that, in 1952, a U.S. Air Force pilot fired his jet's machine guns at a UFO, and that the official report which should have been sent to Blue Book was quashed. 1952 newspaper articles of USAF jets being ordered to shoot down saucers.
• Astronaut Gordon Cooper reported suppression of a flying saucer movie filmed in high clarity by two Edwards AFB range photographers on May 3, 1957. Cooper said he viewed developed negatives of the object, clearly showing a dish-like object with a dome on top and something like holes or ports in the dome. The photographers and another witness, when later interviewed by Dr. James McDonald, confirmed the story. Cooper said military authorities then picked up the film and neither he nor the photographers ever heard what happened to it. The incident was also reported in a few newspapers, such as the Los Angeles Times. The official explanation, however, was that the photographers had filmed a weather balloon distorted by hot desert air. McDonald, 1968 Congressional testimony, Case 41.
• On January 22, 1958, when NICAP director Donald Keyhoe appeared on CBS television, his statements on UFOs were precensored by the Air Force. During the show when Keyhoe tried to depart from the censored script to "reveal something that has never been disclosed before," CBS cut the sound, later stating Keyhoe was about to violate "predetermined security standards" and about to say something he wasn't "authorized to release." What Keyhole was about to reveal were four publicly unknown military studies concluding UFOs were interplanetary (including the 1948 Project Sign Estimate of the Situation and Blue Book's 1952 engineering analysis of UFO motion). (Good, 286-287; Dolan 293-295).
• Astronomer Jacques Vallee reported that in 1961 he witnessed the destruction of the tracking tapes of unknown objects orbiting the Earth. (However, Vallee indicated that this didn't happen because of government pressure but because the senior astronomers involved didn't want to deal with the implications.).
• In 1965, Rex Heflin took four Polaroid photos of a hat-shaped object. Two years later (1967), two men posing as NORAD agents confiscated three prints. Just as mysteriously, the photos were returned to his mailbox in 1993.
• A March 1, 1967 memo directed to all USAF divisions, from USAF Lt. General Hewitt Wheless, Assistant Vice Chief of Staff, stated that unverified information indicated that unknown individuals, impersonating USAF officers and other military personnel, had been harassing civilian UFO witnesses, warning them not to talk, and also confiscating film, referring specifically to the Heflin incident. AFOSI was to be notified if any personnel were to become aware of any other incidents. (Document in Fawcett & Greenwood, 236).
• In 1996, the CIA revealed an instance from 1964 where two CIA agents posed as USAF representatives in order to recover a film canister from a Corona spy satellite that had accidentally come down in Venezuela. The event was then publicly dismissed as an unsuccessful NASA space experiment.

UFOs in ufology.

"Ufology" is the name given to the study of UFO phenomena. Not all ufologists believe that UFOs are necessarily extraterrestrial spacecraft, or even that they are objective physical phenomena. Even UFO cases that are exposed as hoaxes, delusions or misidentifications may still be worthy of serious study from a psychosocial point of view.

UFO researchers: organizations: U.S..

There have been a number of civilian groups formed to study UFO’s and/or to announce their opinions on the subject. Some have achieved fair degrees of mainstream visibility while others remain obscure. The groups listed below have embraced a broad variety of approaches, and have seen a correspondingly wide variety of responses from mainstream critics or supporters.

• Aerial Phenomena Research Organization (APRO) (1952-1988).
• National Investigations Committee On Aerial Phenomena (NICAP) (1956-1980).
• Mutual UFO Network (MUFON) (1969-present).
• Center for UFO Studies (CUFOS) (1973-present) A privately-funded UFO research group founded by J. Allen Hynek, a professor of astronomy at Northwestern University in Chicago. Hynek was also a top scientific consultant for Project Blue Book.
• Fund for UFO Research (FUFOR) (1976-present).
• National Institute of Discovery Science (NIDS) (1996-present).
• National UFO Reporting Center (NUFORC) (1994-present): Run by Peter Davenport; national clearinghouse for UFO reports with phone hotline; listings of reports online.
• Committee for the Scientific Investigation of Claims of the Paranormal.

UFOs in film and television.

Documentary channels, such as the Discovery Channel and the History Channel airs UFO, alien related material from time to time.

As spaceships from other worlds

In a 2006 survey, 24.6% Americans agreed (or strongly agreed) that some UFOs are probably spaceships from other worlds.

Other pages about ufos and aliens.

• Area 51 is a top-secret US airbase also known as - dreamland.
• Black triangles are the name given to UFOs.
• The British UFO Research Association or BUFORA is a British company registered as "BUFORA Ltd".
• Cattle mutilation is the mutilation of cattle by ufos and aliens.
• Condon Report was the informal name of the University of Colorado UFO Project.
• Alien Contactees are people who claim to be in contact with extraterrestrials.
• Crop Circles in the United Kingdom.
• Extraterrestrial Theories are beliefs in UFOs.
• Extraterrestrial Intelligence is the study of extraterrestrial civilizations.
• Extraterrestrial life is life outside of the Earth.
• Alien Life forms are visitors from another world.
• Foo Fighters were described by pilots in World War II as UFOs.
• Greys are extraterrestrial life forms that appear in UFO theories.
• Sightings of UFOs and Aliens.
• Little green men are extraterrestrials with green skin and antennae.
• Majestic 12 is a secret committee of scientists, military leaders, and government officials.
• Men in Black (MIBs), are used in UFO conspiracy theories.
• Disc shaped craft - military flying saucers - date back to World War II.
• Nazi UFOs are advanced aircraft or spacecraft that Nazi Germany developed.
• Project Blue Book: USAF Study of UFO Sightings.
• Project grudge: U.S. Air Force investigation of ufos.
• Project Sign official U.S. government study of unidentified flying objects.
• Rendlesham forest ufo incident.
• UFO Downed near Roswell, New Mexico, in July 1947.
• SETI: organized efforts by humans to detect intelligent aliens.
• UFO Abduction is to be kidnapped by aliens and taken aboard their spaceship.
• UFO Conspiracy Theory believes info about ufos is kept secret.
• The X Files is a US TV show about Mulder and Skully two FBI Agents hunting UFOs.

Debunkery of UFOs.

• Philip Plait (2002). Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the Moon Landing "Hoax". John Wiley & Sons, ISBN 0-471-40976-6. (Chapter 20: Misidentified Flying Objects: UFOs and Illusions of the Mind and Eye.).
• Michael A. Seeds. (1995). Horizons: Exploring the Universe, Wadsworth Publishing, ISBN 0-534-24889-6 and ISBN 0-534-24890-X. (Appendix A).

Psychology.

• Carl G. Jung, "Flying Saucers: A Modern Myth of Things Seen in the Skies" (translated by R.F.C. Hull); 1979, Princeton University Press, ISBN 0-691-01822-7.

Histories of UFOs.

• Richard M. Dolan, UFOs and the National Security State: An Unclassified History, Volume One: 1941-1973, 2000, Keyhole Publishing, ISBN 0-9666885-0-3. Dolan is a professional historian.
• Downes, Jonathan Rising of the Moon. 2nd ed. Bangor: Xiphos, 2005.
• Lawrence Fawcett & Barry J. Greenwood, The UFO Cover-Up (Originally Clear Intent), 1992, Fireside Books (Simon & Schuster), ISBN 0-671-76555-8. Many UFO documents.
• Timothy Good, Above Top Secret, 1988, William Morrow & Co., ISBN 0-688-09202-0. Many UFO documents.
• Kevin Randle, Project Blue Book Exposed, 1997, Marlowe & Company, ISBN 1-56924-746-3.
• Edward J. Ruppelt, The Report On Unidentified Flying Objects, 1956, Doubleday & Co. online. A UFO classic by insider Ruppelt, the first head of the USAF Project Blue Book.
• LeRoy F. Pea, Government Involvement in the UFO Coverup, or earlier title History of UFO Crash/Retrievals", 1988, PEA RESEARCH..

UFOs technology.

• Paul R. Hill, Unconventional Flying Objects: a scientific analysis, 1995, Hampton Roads Publishing Co., ISBN 1-57174-027-9. Analysis of UFO technology by pioneering NACA/NASA aerospace engineer.
• James M. McCampbell, Ufology: A Major Breakthrough in the Scientific Understanding of Unidentified Flying Objects, 1973, 1976, Celestial Arts, ISBN 0-89087-144-2. Another analysis by former NASA and nuclear engineer.
• James M. McCampbell, Physical effects of UFOs upon people, 1986, paper.
• Antonio F. Rullán, Odors from UFOs: Deducing Odorant Chemistry and Causation from Available Data, 2000, preliminary paper.

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