Steven Spielberg's 1977 Close Encounters of the Third Kind is regarded by some ufologists as part of a U.S.-government project to get the public used to the idea of friendly aliens. "Flying saucer" – the term – was coined 60 years ago, when salesman and pilot Kenneth Arnold reported seeing nine objects flying in a "V" formation over Mount Rainier, Washington. Arnold told a reporter on June 24, 1947, that the UFOs flew erratically, fluttering and tipping their wings, like "a saucer if you skip it across water" – and a worldwide subculture was born.

In the six decades since, flying saucers have inspired scores of movies, TV shows and a mini publishing industry. They're supposedly the source of crop circles and cattle mutilations, and they've spawned several cults and a minor religion. Fodder for government commissions, both real and imagined, the mysterious vehicles have also fed government conspiracy theorists, who believe we're being lied to.

"The evidence is overwhelming that some UFOs are intelligently controlled ET spacecraft," says Stanton Friedman, a leading ufologist, who argues further "that the subject represents a cosmic Watergate, that there are no good arguments against these conclusions and that flying saucers and the worldwide government cover-up are the biggest story of the millennium.

"I don't worry much about convincing skeptics," Friedman says. "Those who are willing to look at the scientific evidence will be convinced."

Of course, aliens and UFOs were around long before "flying saucer" was coined. UFOs have been seen for centuries, regarded as spirits, angels, dragons, phantom airships and ghost aircraft.

In 1938, Orson Welles' radio dramatization of The War of the Worlds created mass hysteria. During World War II, allied pilots often reported seeing balls of light following their aircraft. They were nicknamed "foo fighters" and were regarded as German secret weapons. Shortly after the war, ghost rockets were seen throughout Europe. In 1946, at least 1,000 ghost-rocket sightings were reported in Sweden alone.

But never have flying saucers been a bigger part of the zeitgeist than they are now. In 2002, a Roper poll found that one in seven U.S. citizens claim to have seen a UFO or know someone who's had an alien encounter. A recent survey estimated half the U.S. population believes the media is conditioning the public for our first alien encounter. Every year, thousands of UFO sightings are made worldwide. The numbers reported to the authorities or media are difficult to gauge – and even the most die-hard ufologists admit that the majority of sightings can be explained as aircraft, mirages balloons, snow showers or orographic clouds.

Author Jenny Randles has written 50 books on UFOs and the paranormal, but found no evidence of alien visitors or government cover-up .

One reliable source, the U.S. Air Force's Project Blue Book, a massive 20-year study of flying saucers, received 15,000 UFO reports between 1952 and 1970.

In 1997, members of the Heaven's Gate cult, led by Marshall Herff Applewhite, committed mass suicide, believing they would be spirited away on a flying saucer. Longer-lived UFO cults include the Aetherius Society and the International Raelian Movement, founded in 1974 by Rael, aka Claude Vorilhon, a former French motor-racing writer.

Rael was told by an alien called Eloha that the human race was the product of DNA experimentation and that the Bible and other religious texts actually refer to contact with aliens rather than with God and his messengers. Rael, who thinks he is related to Jesus and Muhammad, has managed to attract several thousand followers, who are planning to make their headquarters in Las Vegas.

The writings of Erich von Däniken, much like Rael, claim that alien astronauts who visited Earth were mistaken for gods and included in legends, folklore and religious texts and rituals.

Days after Arnold's sighting, in July 1947, the Roswell Daily Record claimed that the Roswell Army Air Field had recovered a crashed flying saucer. The Army explained the crash as the wreckage of a weather balloon. The incident was largely forgotten until the late 1970s, when eyewitnesses began to come forward claiming the balloon was an alien craft.

The Roswell case has become the foundation stone for belief that the U.S. government secretly recovered alien technology and collaborated with extraterrestrials. The Air Force has always denied this, and it published The Roswell Report: Fact vs. Fiction in the New Mexico Desert to detail its side of the argument.

In 1948 and 1949, strange green fireballs were seen exploding over the skies of New Mexico. Many feared they were guided missiles sent by the Soviet Union. However, a conference organized by the Air Force concluded that they were unusual meteors.

The '50s saw a rash of "contactees," who claimed they had meetings with aliens and rode in their spaceships. The most famous contactee was George Adamski, who allegedly met an alien called Orthon in the California desert Nov. 20, 1952. These "friendly" space people warned of the dangers of scientific progress and gave spiritual messages for humanity.

The themes were reflected in many flying saucer movies of the time, such as The Day the Earth Stood Still (Robert Wise, 1951). In Brazil, farmer Antonio Villas Boas claimed a space woman captured and raped him in 1957.11

Sex with aliens is a recurring theme in abduction stories going back to the '50s.

Amateur UFO groups and clubs began cropping up. In the United States, the two most important groups were the Aerial Phenomena Research Organization, or APRO, founded by Jim and Coral Lorenzen in 1952, and the National Investigations Committee on Aerial Phenomena, or NICAP, which began in 1956. NICAP, under the leadership of UFO author Donald E. Keyhoe, supported the idea that UFOs were extraterrestrial craft.

Many also allege that the Air Force has tried to cover up evidence of UFOs. Ironically, many CIA operatives were NICAP members, including Vice Adm. Roscoe H. Hillenkoetter, who sat on the board of directors until 1962.

The contactees were largely ignored by scientific UFO investigators until the case of Betty and Barney Hill, who reported seeing a UFO following their car the night of Sept. 19, 1961. When they returned home, they found they couldn't remember a long section of their journey. Under hypnosis, the couple recalled being abducted and subjected to intimate medical examinations. Their situation came to worldwide attention when John G. Fuller published The Interrupted Journey in 1966.

In 1969, the Colorado University UFO Project, headed by Dr. Edward Uher Condon, published the results of a two-year study of UFO files collected by the Air Force's Project Blue Book. The Condon Report concluded that the study of UFOs was not scientifically valuable and the Air Force closed down the project. Ufologists have always regarded Condon's report as a whitewash. Astronomer J. Allen Hynek, an adviser to the project, was so dissatisfied with its findings that he created the Center for UFO Studies in 1974 to continue the scientific study of UFOs.

Despite Condon's findings, UFOs still fascinated the public, and reported sightings continued. In the '70s, abduction reports escalated sharply.

Steven Spielberg's Close Encounters of the Third Kind in 1977 is regarded by some ufologists as part of a U.S.-government-backed project to get the public used to the idea of friendly aliens. The film had such an impact on the British House of Lords that it held a three-hour debate on alien abductions in 1979. Her Majesty's government, however, decided UFOs were not alien spacecraft and were not a threat to the nation.

The '80s started with a bang. The Roswell Incident, by Charles Berlitz and William L. Moore, portrayed the Roswell crash as part of a much larger cover-up, and opened the floodgates for increasingly bizarre stories featuring the recovery of flying saucers and alien bodies.

This autographed sketch of the first "flying saucer" was made by Kenneth Arnold, the pilot whose UFO encounter in 1947 inspired the term.

Whitley Strieber's reported abduction experiences, including an examination by anal probe, became the basis for the best-selling Communion: A True Story in 1987. The writings of Budd Hopkins, David Jacobs and John E. Mack reinforced the idea that millions of people are being regularly abducted.

Government conspiracy, alien abduction and Roswell fueled the highly successful TV series The X-Files (1993-2002) and films like Independence Day (Roland Emmerich, 1996) and Men in Black (Barry Sonnenfeld, 1997). During this period, ex-government whistle-blowers came forward.

In 1995, Alien Autopsy, a film by Ray Santilli, was released. The London filmmaker said he obtained it from an old U.S. cameraman. It is supposed to be genuine footage of the autopsy of an alien corpse recovered from the Roswell crash of 1947. Most regard it as a hoax.

In 2000, Alfred Webre's book Exopolitics: Towards a Decade of Contact spawned Exopolitics, which has gained a lot of supporters who feel the existence of UFOs does not have to be scientifically proven. They say there is enough evidence to accept that UFOs are spaceships piloted by extraterrestrials. Their goal is to put pressure on the United States and other governments to disclose the truth that they have been secretly working with the aliens since the 1940s.

In 2005, a large document allegedly written in the late 1970s came to light that claimed that six aliens were recovered from the Roswell crash. An alien called EBE 1 was said to have survived and organized a team of specially trained humans to visit his home planet, Serpo. The story goes that 12 humans stayed there from 1965 to 1978, two remained and the others either died on the planet or when they returned to Earth. The tale represents the flavor of contemporary UFO rumor.

"The vast majority of UFO sightings can be explained in mundane terms, writes UFO expert and author Jenny Randles. "I have found almost no sustainable evidence that any UFO encounter is caused by alien visitors or spacecraft and no support for the idea that the powers that be are covering up anything much beyond their own ignorance as to the cause of the residue of unsolved cases."

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Many online resources detail parts of the UFO story:

The FBI details reports on UFOs and cattle mutilations, Majestic 12 and Roswell.

Several UFO reports are published by the British Ministry of Defence.

The French National Space Studies Center has posted 1,600 UFO reports.

The Project Blue Book Archive attempts to put all of the Air Force's files from its UFO investigation online.

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