"UFO" redirects here. For other uses, see UFO (disambiguation).
Photograph of alleged UFO, New Jersey, 31 July 1952
An unidentified flying object (usually abbreviated to UFO or U.F.O.) is any unusual apparent object 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. There has been some debate in the scientific community about whether any scientific investigation into UFO sightings is warranted.
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).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 the United 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, though today the term UFO is often used for any unexplained sighting regardless of whether it has been investigated. 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).
The Kenneth Arnold sightings
Main article: Kenneth Arnold Unidentified Flying Object Sighting
This shows the report Kenneth Arnold filed in 1947 about his UFO sighting.
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 near Mount 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.
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,
