A UFO is an unidentified flying object. More specifically, it is some atypical or seemingly-unexplainable aerial phenomenon. UFO's are believed by many people to be extraterrestrial spacecraft, though there has yet to be any widely-convincing discovery of extraterrestrial technology. "Unidentified Aerial Phenomenon" (UAP) may be a better name, but "UFO" has stuck.
The large majority of UFO sightings are sightings of known phenomena, both of natural phenomena and of human technology, though sometimes of unusual ones. Objects described as UFO's include bright stars, planets, especially Venus, the Moon, meteors, re-entering Earthling spacecraft, artificial satellites, airplanes, including advertising airplanes, missile launches, balloons, birds, clouds, kites, flares, ground lights, searchlights, mirages, cloud reflections like sundogs and subsuns, etc. There are some unusual phenomena like ball lightning that might almost be called "real UFO's", but they are unlikely to be extraterrestrial spacecraft. The balloons include fire balloons, small hot-air balloons powered by candles. These can look like glowing blobs. They are sometimes launched as pranks, and since they are outlawed in several places as a fire hazard, the pranksters may be unwilling to reveal themselves.
Of the more detailed encounters, as opposed to distant lights and the like, some are hoaxes, some are fantasies that the tellers came to believe, and some are nightmares or sleep-paralysis effects. Several detailed pictures and videos of alleged extraterrestrial spacecraft are known or suspected fakes.
Strange apparitions in the sky go back a long way in human history. In the Bible, Ezekiel's vision and the Star of Bethlehem. The vimanas, flying chariots and castles of Hindu literature. The Fata Morgana. The Flying Dutchman ghost ship.
This paleo-UFOlogy is commonly associated with Erich von Däniken with his ancient astronauts, but discussion of it goes back to at least 1953, with Desmond Leslie's and George Adamski's Flying Saucers Have Landed.
The Fata Morgana is floating castles and the like seen in the distance. Their name is the Italian version of the name of Morgan le Fay or Morgan the Fairy, an Arthurian character. She supposedly created them, presumably to mess with sailors' minds. That one turns out to be a mirage.
In the late eighteenth century, the scientific community had some skepticism about a certain aerial phenomenon that turned out to be excessive, skepticism about alleged falls of extraterrestrial rocks and lumps of iron. Some of them believed that these objects were condensations in the upper atmosphere, much like hailstones. That supposed atmospheric origin is what led to these rocks being called meteorites. Some others believed that these rocks were ejected from volcanoes or transported by windstorms. Some more others believed that they were Earth rocks that had been struck by lightning.
But some others believed that they were extraterrestrial objects, notably Ernst Florens Chladni. From his legal training, he knew that ordinary people can be accurate in their recollections of sudden, fast, and unusual events. He also noted meteorites' unusual composition, and from reports of their falls, he deduced that they were falling far too fast to have a terrestrial origin.
In 1803, the French Academy of Sciences dispatched Jean-Baptiste Biot to check out a case of a meteorite fall at the town of L'Aigle. He discovered that people all over L'Aigle saw this object fall, people across all social classes, people who usually did not interact with each other. He also discovered the presence of rocks that were much alike, and unlike rocks known to be from the area. He wrote up his findings in a report, and that report was widely circulated and republished. He thus convinced the scientific community that meteorites were extraterrestrial rocks and iron lumps.
Some UFOlogists have compared UFO's to meteorites, comparing skepticism about extraterrestrial spacecraft to skepticism about extraterrestrial rocks. But UFOlogy has yet to produce its counterpart of the L'Aigle event.
Around the turn of the twentieth century, there were numerous sightings of "mysterious airships" in the United States, New Zealand, and elsewhere. Many of them were journalistic hoaxes, tongue-in-cheek stories, and some of them turned out to be celestial objects like the star Betelgeuse and pranks like a balloon and a bird with burning objects attached. No physical evidence of the alleged air vehicles ever turned up, and the sightings faded.
In World War II were several sightings of "foo fighters", bright objects that would follow warplanes around. UFO skeptic Philip Klass once noted a case of some pilots who saw a "searchlight airplane" that followed them around. Some of the pilots fired upon it, but none claimed to have hit it. It turned out to be the planet Venus. Celestial objects sometimes seem to follow their observers around, because they brightness and direction changes far too little to be detected as their observers move. UFO skeptic Donald Menzel recalled from his childhood watching the Moon follow him around, and Philip Klass once noted that the planet Mars followed him around as he drove at night.
In 1946, there were lots of "ghost rockets" seen in Sweden. One notable picture of one of them likely shows a meteor.
The modern era
It started in June 24, 1947, when Kenneth Arnold saw from his private plane nine objects traveling in a line near Mt. Rainier. They skipped like saucers, he said, something that provoked some journalist to coin the term "flying saucer". Before long, lots and lots more people saw aerial dishware. It seemed like silly-season stuff, but on January 7, 1948, a military pilot's plane was shot down by an extraterrestrial spacecraft, or so it seemed. Kentucky Air National Guard pilot Captain Thomas F. Mantell was dispatched to check out a silvery, metallic object that had been seen over a wide area. He climbed higher and higher, but he could not reach it. His plane eventually went into a dive and crashed. Instead of being shot down, Captain Mantell likely passed out from lack of oxygen and lost control of his plane. The object that Captain Mantell was chasing was identified as the planet Venus by US Air Force consultant J. Allen Hynek, from how another military pilot was discovered to have been chasing that planet. But that did not fit. Donald Menzel proposed a sundog, but that didn't fit either. The most likely explanation is a high-altitude balloon. These balloons were originally developed as spy balloons, complete with extreme secrecy in these balloons' first years.
The United States Air Force got into investigating flying saucers out of concern that they might be secret Soviet airplanes and balloons. Its earlier investigations were not handled very well, something that provoked claims that the USAF was covering up what it knew. Around 1952, USAF investigator Captain Edward J. Ruppelt came up with the name UFO, short for Unidentified Flying Object. That was because "flying saucer" did not describe many sightings very well, and because it sounded silly.
Also in 1952 was an alleged meeting with an extraterrestrial visitor. George Adamski went out into the southern California desert and returned with a strange story. He claimed to have met a young-looking man in a jumpsuit who claimed to be from the planet Venus and who was very concerned about Earthlings' nuclear-bomb development. George Adamski was the first UFO contactee, and he inspired several imitators, people who claimed to have close encounters of the friendly kind with UFOnauts. It must be noted that contactees are disdained by many UFOlogists as the lunatic fringe of their movement.
An alternative close-contact scenario emerged in 1961, the UFO abduction. Betty and Barney Hill were driving one night when they reported being chased by UFO's. They turned out to be planets Jupiter and Saturn. Some days later, she started getting nightmares about UFOnauts abducting her and doing clumsy medical exams on her. A psychiatrist examined her and a reporter asked him if he believed that Betty Hill had been abducted by UFOnauts. He answered "Absolutely not!" The Hills were not the first. A few years before, in southern Brazil, Antonio Vilas-Boas claimed that he was dragged into a spacecraft by some spacemen, examined, and made to have sex with a spacewoman. After successfully raping him, she pointed to her belly and then pointed upward, making him feel like a "stallion". His captors then showed him around their spacecraft and then out of it. But his case did not get a lot of publicity at first.
The USAF continued to investigate UFO cases into the late 1960's. In 1966, J. Allen Hynek proposed that some UFO's in Michigan were swamp gas, an explanation that was widely ridiculed. A more plausible hypothesis for them is fire balloons. The USAF sponsored some investigations of notable UFO cases led by physicist Edward Uhler Condon. That report concluded that UFO's were most likely not extraterrestrial spacecraft, though it left several cases unexplained. UFO skeptics like Philip Klass later filled in some of its gaps. That aside, the US Air Force stopped officially investigating UFO's in 1968.
UFO sightings and UFO controversies have continued to the present day, but without any progress in getting strong evidence of the putative extraterrestrial spacecraft. Most recently, there has been a fall-off in UFO reports and interest in UFO's that is apparently due to the proliferation of smartphones and digital cameras (TWILIGHT OF THE GULLIBLE | More Intelligent Life). These devices could provide a L'Aigle moment for UFOlogy, but instead, it appears to be an anti-L'Aigle.
J. Allen Hynek and others have proposed various classifications of UFO's. Here is Hynek's classification with some proposed extensions:
- Nocturnal lights
- Daylight disks
- Close encounters of the first kind: close enough to see a lot of detail (< 500 ft, 150 m)
- Close encounters of the second kind: physical evidence
- Close encounters of the third kind: occupants or UFOnauts evident
- Close encounters of the fourth kind: abductions
- Close encounters of the fifth kind: friendly contacts, including communication
The lowest member of Hynek's list is what inspired the title of the movie Close Encounters of the Third Kind. Likewise, abductions may be called close encounters of the involuntary kind and contacts close encounters of the friendly kind.