- Unidentified flying objects (UFOs) are airborne objects—or optical phenomena that seem like airborne objects—that an onlooker is unable to identify.
- UFOs first became a major subject of public interest after World War II, possibly sparked by the development of rocket technology.
- Some interpret the sighting of UFOs as evidence that extraterrestrial life exists and has visited Earth.
- The first widely publicized UFO sighting took place in 1947, when businessman Kenneth Arnold claimed he spotted a group of high-speed, crescent-shaped, flying objects while piloting his own plane near Mount Rainier in Washington.
- The term “flying saucer” originated from a misprint of Kenneth Arnold’s account of his own sighting, in which he described seeing the crescent-shaped objects moving through the air “like saucers skipping on water;” a newspaper report misstated that the objects themselves were saucer-shaped, thus birthing the idea of the flying saucer.
- The U.S. Air Force undertook Project Sign in 1948, an inquiry that was intended to investigate the spate of UFOs sightings that had recently been reported.
- Many researchers involved with Project Sign were originally convinced that UFOs were high-tech Soviet aircraft; a minority ascribed to the extraterrestrial hypothesis (ETH).
- Project Sign gave way to Project Grudge in 1949, which in turn gave way to Project Blue Book in 1952—the most lasting of the U.S. government’s inquiries into the UFO question. Project Blue Book remained open from 1952 to 1969. The project had its headquarters at Wright-Patterson Air Force Base in Dayton, Ohio.
- In the 17 years that Project Blue Book was in operation, it recorded over 12,000 sightings.
- Sightings that were recorded by Project Blue Book were categorized into two groups: those that could be associated with a known phenomenon, be it atmospheric, astronomic, or man-made, and those which could not be readily associated with any identifiable cause.
- In 1953 the Central Intelligence Agency (CIA) created the Robertson Panel, a panel of scientists helmed by physicist H.P. Robertson that was charged with reviewing the findings of Project Blue Book.
- The Robertson Panel came to the conclusions that the vast majority of UFO sightings could be explained by natural phenomena, that the UFOs sighted posed no security risk to the U.S., and that there was no evidence in Project Blue Book’s records that proved the existence of extraterrestrials.
- Parts of the Robertson Panel’s findings were not revealed until 1979, a delay that added fuel to the flames of various conspiracy theories involving the idea of a government cover-up.
- Another inquiry was opened by the U.S. Air Force in 1966, which—under the leadership of physicist Edward U. Condon—was tasked with investigating 59 compelling but inexplicable sightings originally recorded during Project Blue Book. The results of the inquiry were included in a report called Scientific Study of Unidentified Flying Objects, less formally referred to as the Condon Report.
- The Condon Report also found no evidence for the existence of extraterrestrials. This finding contributed to the decision to shutter Project Blue Book in 1969.
- A small minority of scientists continued to subscribe to the ETH. J. Allen Hynek, an astronomer at the Ohio State University and then at Northwestern University who participated in the Projects Sign, Grudge, and Blue Book investigations, is one of the better-remembered scientists who continued to advocate for the idea. He founded his own privately run research group called the Center for UFO Studies (CUFOS) in 1973.
- Governmental scrutiny of the UFO phenomenon was revived in the 21st century with the Advanced Aviation Threat Identification Program (AATIP), a secret (albeit unclassified) program run by the U.S. Department of Defense (DoD). According to the DoD, AATIP operated from 2007 to 2012, at which point the program’s funding was diverted elsewhere.
- Canada’s government is the only one besides that of the U.S. that has kept relatively extensive records on its citizens’ UFO sightings. Other countries—including the United Kingdom, Sweden, Denmark, Australia, and Greece—have kept scantier records.
- In some countries (for example, those of the former Soviet Union and the Peoples’ Republic of China), UFO sightings resulted from secret military tests that the countries’ people weren’t made aware of. In some cases, the governments involved encouraged their citizens to believe that the objects were of extraterrestrial origin in order to obfuscate the true nature of the experiments.
- There are numerous natural phenomena that have been employed to explain UFO sightings: they include the fact that the planet Venus is often mistaken for a flying object, that the reflections on windows and eyeglasses can produce superimposed images, or that the halo effect that camera lenses sometimes lend to illuminated objects can resemble a saucer-like shape.
- Psychologists often attribute “abduction” stories to sleep paralysis, a commonly experienced sleep disorder whereby a person—while falling asleep or waking up—is conscious but unable to move their body.