An unidentified flying object (UFO) is an object or event seen in the sky that has not yet been identified or explained. The term UFO was created when the United States Air Force studied reports of flying saucers and realized the objects described had many different shapes, not just saucers or discs. UFOs are also called unidentified aerial phenomena or unidentified anomalous phenomena (UAPs). After investigation, most UFOs are found to be known objects or natural events in the sky, while a small number remain unexplained.

People have reported unusual sky sightings since at least the 3rd century BC. However, UFOs became widely discussed in culture after World War II, especially during the Space Age. Governments, such as the United States with Project Blue Book and the United Kingdom with Project Condign, as well as organizations and individuals, have studied UFO reports over time. These studies have not confirmed the claims made by some people who believe UFOs are evidence of extraterrestrial life, advanced creatures, interdimensional contact, or time travelers.

Despite many years of promoting these ideas in media and by believers, strong evidence to support these claims has not been found. Scientists and groups like the Committee for Skeptical Inquiry explain UFOs as natural events, human-made technology, misunderstandings, or hoaxes. Some beliefs about UFOs have influenced new religions, but social scientists say the continued interest in UFO stories is an example of modern folklore and mythology that can be understood through psychological and social explanations.

The challenge of explaining events or objects that are temporarily or permanently unknown is a topic in the philosophy of knowledge, called epistemology. The U.S. government has two groups focused on collecting and analyzing UFO data: NASA’s UAP independent study team and the Department of Defense’s All-domain Anomaly Resolution Office.

Terminology

During the late 1940s and throughout the 1950s, UFOs were often called "flying saucers" or "flying discs" because of reports from the Kenneth Arnold incident. The term "Unidentified Flying Object" (UFO) was first used in 1947. The abbreviation "UFO" was created by Captain Edward J. Ruppelt for the United States Air Force. He explained, "The term 'flying saucer' is confusing when describing objects of many different shapes and abilities. For this reason, the military prefers the more general term: unidentified flying objects."

The term UFO became common during the 1950s, first in technical writing and later in everyday language. "Unidentified Aerial Phenomenon" (UAP) was first used in the late 1960s. UAP has been used more often in the 21st century because some people associate "UFO" with negative ideas. UAP is sometimes described as "unidentified anomalous phenomenon." While a UFO technically refers to any object in the sky that cannot be identified, in modern culture, the term UFO is often used to describe spacecraft from other planets. The term "extra-terrestrial vehicle" (ETV) is sometimes used to separate this idea from explanations that are entirely related to Earth.

Identification

Studies show that after careful investigation, most UFOs can be explained as common objects or natural events. A USAF study from 1952–1955 used these categories to classify UFO reports: "Balloon; Astronomical (such as stars or planets); Aircraft; Light phenomenon; Birds, clouds, or dust; Insufficient information; Psychological manifestations; Unknown; and Other." Identified causes of UFO sightings include:

A 1979 study by CUFOS researcher Allan Hendry found, like other investigations, that less than one percent of UFO cases he studied were hoaxes. Most sightings were honest mistakes, where people misidentified ordinary things. Hendry believed these errors often happened because of lack of experience or incorrect observations. Astronomer Andrew Fraknoi disagreed with the idea that UFOs are spaceships from other planets. He addressed the "overly trusting coverage" of UFO stories in books, movies, and media by teaching students to use critical thinking. He told them, "Being a good scientist is similar to being a good detective." Fraknoi explained that UFO reports "may seem mysterious at first," but "the more you look into them, the more likely you are to find that there is less to these stories than it appears."

History

People have always looked at the sky and sometimes saw unusual sights, such as comets, bright meteors, planets visible without a telescope, planetary conjunctions, and atmospheric effects like parhelia and lenticular clouds. One famous example is Halley’s Comet, which was first recorded by Chinese astronomers in 240 BC and possibly as early as 467 BC as a strange light in the sky.

Halley’s Comet visits the inner solar system every 76 years. In ancient times, people often saw it as a unique event, not knowing it would return. Many historical records described it as a supernatural sign or religious omen. While some modern people compare religious symbols in old paintings to UFOs, art historians say these images were meant to represent traditional religious ideas.

During World War II, pilots in the Pacific and European theaters reported seeing glowing, round fireballs called "foo fighters." Some believed these were caused by St. Elmo’s fire, the planet Venus, oxygen deprivation, or German weapons. In 1946, the Swedish military collected over 2,000 reports of unidentified objects in Scandinavia, France, Portugal, Spain, Italy, and Greece. These objects were called "Russian hail" or "ghost rockets" because people thought they might be Russian tests of German rockets, but most were later identified as meteors.

After Kenneth Arnold’s 1947 sighting of "bat-like aircraft" near Mount Rainier, the term "flying saucers" became widely known. A Gallup poll found that 90% of Americans had heard the term, but most did not know what flying saucers were. The Roswell incident in 1947 involved a farmer finding parts of a balloon, which the military took. In the 1950s, groups called "saucer clubs" formed, inspired by science fiction fan clubs. Books like The Flying Saucers Are Real claimed UFOs were linked to atomic weapons and alien visits.

In 1952, a UFO scare in Washington, D.C., led officials to worry that real enemy planes might be mistaken for UFOs. A 1957 survey showed over 25% of Americans believed UFOs could be from space. The 1959 book Flying Saucers: A Modern Myth by Carl Jung explored UFOs as a cultural idea.

The U.S. Air Force studied UFOs through projects like Sign, Grudge, and Blue Book, cataloging over 12,000 sightings. However, the CIA resisted full declassification of UFO records, though some officials supported transparency. In 1969, the Air Force stopped investigating UFOs after a study concluded that UFO research had not added to scientific knowledge.

From the 1960s to 1990s, UFOs were a popular topic in American culture. In 1961, the Hills’ alien abduction story gained attention. A 1966 Gallup poll found that 5% of Americans had seen a UFO, and 96% had heard of them. Media efforts to explain UFOs, like a 1966 TV special with Walter Cronkite, argued that UFOs were not real. Despite these efforts, UFOs remained a cultural fascination, inspiring movies like Close Encounters of the Third Kind and Alien. TV shows and books continued to explore UFO stories, keeping the topic in the public eye.

Investigations of reports

UFOs have been studied by many groups over the years. These studies had different levels of detail and scientific quality. Governments and independent researchers in the United States, Canada, the United Kingdom, Japan, Peru, France, Belgium, Sweden, Brazil, Chile, Uruguay, Mexico, Spain, and the Soviet Union have looked into UFO reports at different times. No official government study has ever said UFOs are definitely real, physical objects from space or a threat to national defense.

Some well-known government studies include Sweden’s ghost rockets investigation (1946–1947), the U.S. Air Force’s Project Blue Book (1947–1969), the U.S. Army/Air Force’s secret Project Twinkle (1948–1951), the USAF’s Project Blue Book Special Report No. 14 by Battelle Memorial Institute, and Brazil’s 1977 Operação Prato (Operation Saucer). France has studied UFOs since 1977 through GEPAN/SEPRA/GEIPAN, part of its space agency, CNES. Uruguay has had a similar study since 1989.

In 2008, Brazil’s National Archives began receiving UFO-related documents from the Aeronautical Documentation and History Center. These documents cover UFO sightings in Brazil from 1952 to 2016.

In 1968, Chile’s SEFAA (previously CEFAA) started collecting UFO reports from the public, pilots, and the Chilean Air Force. This work was led by Sergio Bravo Flores, who founded the Chilean Committee for the Study of Unidentified Space Phenomena. Today, SEFAA is part of the Chilean Air Force.

In Canada, the Department of National Defence has studied UFO reports. It has looked into crop circles in Alberta and still considers the Falcon Lake incident in Manitoba and the Shag Harbour UFO incident in Nova Scotia unsolved. Early Canadian studies included Project Magnet (1950–1954) and Project Second Storey (1952–1954), supported by the Defence Research Board.

U.S. investigations into UFOs include studies by the Air Force and other agencies. Thousands of documents released under FOIA show that U.S. intelligence agencies, such as the Defense Intelligence Agency (DIA), FBI, CIA, National Security Agency (NSA), and military intelligence groups, have collected UFO information.

In 1947, after a large increase in UFO sightings, the U.S. Army Air Forces (USAAF) and FBI started a formal investigation. They studied sightings like Kenneth Arnold’s, using top scientists to determine if the objects were real. The USAAF concluded that the objects were real and not just natural phenomena or man-made.

A review by the Air Materiel Command at Wright Field also found the objects were real, describing them as metallic, disc-shaped, and highly maneuverable. This led to the creation of the Air Force’s Project Sign in 1947. In 1949, Project Sign’s report said some UFOs looked like real aircraft, but their origin was unclear.

In 1948, Project Sign’s investigators wrote a secret report suggesting UFOs might be extraterrestrial. However, the report was destroyed by Air Force leadership. The report’s existence was later revealed by insiders like astronomer J. Allen Hynek and Capt. Edward J. Ruppelt.

In 1952, the CIA’s Office of Scientific Investigation (OS/I) studied UFOs and concluded they were real physical objects that could threaten national security. The OS/I urged the National Security Council to investigate UFOs further. This led to the creation of the Robertson Panel, which later dismissed UFOs as a threat.

Project Sign was later replaced by Project Grudge in 1948. In 1951, Project Grudge became Project Blue Book, led by Ruppelt. Hynek, a scientist who worked on Project Blue Book, later criticized the project for not following scientific methods. He founded the Center for UFO Studies (CUFOS) after leaving government work. Other groups, like MUFON, also study UFOs.

Air Force Regulation 200-2 (1953–1954) defined an Unidentified Flying Object (UFOB) as any airborne object that does not match known aircraft or missiles. The regulation said UFOBs should be studied as possible threats to U.S. security and to understand their technical features.

Studies

UFOs have become a common topic in modern culture, and the social interest in them has been studied by experts in sociology and psychology. Some people argue that all UFO evidence comes from personal stories and can be explained by ordinary natural events. Others say that scientific knowledge about UFOs, beyond what is shared in the media, is limited and more research is needed. Studies show that most UFO sightings are actually misidentifications of common objects or natural events, such as planes, balloons, satellites, and stars. A small number of sightings are hoaxes.

Less than 10% of UFO reports remain unexplained after proper investigation and can be called truly unidentified. Steven Novella says that some people believe these unexplained sightings are alien spacecraft, but there is also a possibility that they are natural events that are hard to identify because of missing information or unclear reports. Novella notes that UFO supporters often suggest unusual, untested explanations to support the idea of alien spacecraft, which goes against the scientific principle of choosing the simplest explanation.

Historically, UFO research has not been widely accepted by mainstream science. Scientists have generally considered UFO sightings more as a cultural topic than a serious scientific issue. Research on UFOs is rarely published in major scientific journals. In 1969, the U.S. government stopped official UFO studies after a scientist, Edward Condon, said further research would not help science. In September 2023, NASA announced the first appointment of a NASA Director of UAP Research, Mark McInerney, to study these events in a scientific and open way.

Despite studies by governments and private groups, UFO research is not seen as a legitimate scientific field by many academics. It is often called pseudoscience, which refers to ideas that claim to be scientific but lack proper evidence, testing, or scientific methods. Some studies suggest that the way science is communicated about UFOs and aliens may confuse the public and discourage scientific research.

Jacques Vallée, a scientist and UFO researcher, pointed out problems in UFO studies, including the myths and cult-like beliefs sometimes linked to UFO sightings. He noted that hundreds of scientists, called "the invisible college," continue to study UFOs on their own time.

In 2021, astronomer Avi Loeb started The Galileo Project to find scientific proof of alien technology near Earth. In Germany, the University of Würzburg is creating sensors to detect and study aerial objects. A 2021 Gallup poll showed that more Americans believe some UFOs are alien spacecraft, rising from 33% in 2019 to 41% in 2021. Gallup said increased news coverage and government attention helped change public views.

In 2022, NASA began a nine-month study to create a plan for investigating UAP. In 2023, the RAND Corporation analyzed over 100,000 UAP reports in the U.S. from 1998 to 2022. The study found that UAP reports were more common near military areas, where training happens.

Besides personal sightings, UFO reports sometimes include physical evidence studied by governments, such as Project Blue Book and the French GEPAN/SEPRA. In 1998, the Sturrock panel reviewed cases with physical evidence.

The Committee for Skeptical Inquiry (CSI) has long studied UFO claims. For example, they helped show that crop circles in Indonesia were man-made, not caused by aliens. A scientist from Indonesia’s space agency said scientists classify UFOs as pseudoscience.

Many governments have studied UFOs, but most stopped after concluding there was no scientific benefit. Some classified studies, like the U.S. CIA’s Robertson Panel and the UK’s Flying Saucer Working Party, also found no evidence of alien spacecraft. However, some reports, like the Belgian military study of unusual shapes in the sky, suggested UFOs might be real but did not confirm they were alien.

In the 21st century, military and government officials have shared personal accounts and official statements about UAP. Reports by the Navy, Pentagon, and U.S. intelligence agencies have increased public and institutional interest in the topic.

In popular culture

Since the 1950s, UFOs have become a common topic around the world. Gallup Polls show UFOs are among the most well-known subjects. In 1973, a survey found that 95% of people had heard of UFOs, while only 92% had heard of U.S. President Gerald Ford in a 1977 poll taken nine months after he left office. A 1996 Gallup poll found that 71% of Americans believed the U.S. government knew more about UFOs than it shared with the public. A 2002 Roper Poll for the Sci-Fi Channel found similar results: 48% thought aliens had visited Earth, 56% believed UFOs were real spacecraft, and 70% felt the government was hiding information about UFOs or extraterrestrial life.

Flying-saucer designs appeared in science fiction and other popular culture. Examples include the C57D in Forbidden Planet (1956), the saucer-shaped spaceship Jupiter 2 in Lost in Space, and the saucer section of the USS Enterprise in Star Trek. UFOs and aliens have been featured in many movies. The secrecy around the Nevada base called Area 51 has made it a frequent topic of conspiracy theories and a lasting part of UFO culture. In July 2019, more than a million people signed up for a humorous Facebook event suggesting a visit to Area 51, and nearly a million more expressed interest. Two music festivals in rural Nevada, "AlienStock" and "Storm Area 51 Basecamp," were created to use the event's popularity. About 150 people reached the Area 51 entrance, and the festivals had 1,500 attendees.