An unidentified flying object (UFO) is an object or event seen in the sky that has not yet been identified or explained. The term was first used when the United States Air Force (USAF) studied reports of flying saucers and found that the shapes reported were too varied to all be called saucers or discs. UFOs are also called unidentified aerial phenomena or unidentified anomalous phenomena (UAPs). After investigation, most UFOs are recognized as known objects or natural weather events, while a few remain unexplained.

People have reported strange objects in the sky since at least the 3rd century BC. However, UFOs became widely discussed 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 groups and individuals, have studied UFO reports over the years. These studies have not confirmed the unusual claims made by some people who believe UFOs are linked to advanced alien technology, hidden creatures, or otherworldly events.

Despite many years of promotion by believers and in movies and books, strong evidence to support these claims has not been found. Scientists and groups that question unusual claims, like the Committee for Skeptical Inquiry, explain that UFOs are often caused by natural events, human-made objects, misunderstandings, or deliberate tricks. Some beliefs about UFOs have influenced new religions, but social scientists say the continued interest in UFOs is similar to old stories and myths, which can be explained by how people think and behave.

The challenge of understanding objects or events that cannot be easily explained is part of the study of knowledge, called epistemology. The U.S. government has two groups that collect and study 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 through 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 acronym "UFO" was created by Captain Edward J. Ruppelt for the USAF. He explained, "The term 'flying saucer' is misleading when describing objects of many different shapes and abilities. Because of this, the military prefers the more general term: unidentified flying objects."

The term UFO became widely used during the 1950s, first in technical writing and later in everyday language. "Unidentified Aerial Phenomenon" (UAP) was introduced in the late 1960s. UAP has been used more often in the 21st century because some people have negative feelings about the word "UFO." UAP is sometimes described as "unidentified anomalous phenomenon." While a UFO technically refers to any object that cannot be identified, in modern culture, the term UFO is often used to mean alien spacecraft. The term "Extra-Terrestrial Vehicle" (ETV) is sometimes used to distinguish 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: "balloons, stars, planes, lights, birds, clouds, dust, etc., not enough information, psychological experiences, unknown, and other." Identified causes of UFO reports include:

A 1979 study by CUFOS researcher Allan Hendry found, like other investigations, that less than one percent of the cases he studied were hoaxes. Most sightings were honest mistakes in identifying ordinary things. Hendry believed these mistakes often happened because of lack of experience or errors in seeing something clearly. Astronomer Andrew Fraknoi did not believe UFOs are spaceships from other planets. He responded to books, movies, and shows that are too trusting by teaching students to use critical thinking to examine such claims. He told his students, "Being a good scientist is similar to being a good detective." Fraknoi said that UFO stories may seem mysterious at first, but more investigation often shows they are not as strange as they seem.

History

People have always looked at the sky and sometimes saw strange things. These included events like comets, bright meteors, planets visible without a telescope, when planets appear close together, and unusual cloud shapes like parhelia and lenticular clouds. One famous example is Halley’s Comet. Chinese astronomers first recorded it in 240 BC and possibly as early as 467 BC. They called it a strange "guest light" in the sky.

Halley’s Comet visits the inner solar system every 76 years. In ancient times, people often saw it as a one-time event because they didn’t know it would return. Some ancient writings described it as a sign from the gods or supernatural events. Later, some people compared UFO sightings in medieval art to religious symbols, but art experts say these images usually had traditional religious meanings.

During World War II, pilots in the Pacific and Europe reported glowing fireballs called "foo fighters." Possible explanations included natural events like St. Elmo’s fire or the planet Venus, hallucinations, or German weapons. In 1946, Sweden collected over 2,000 reports of unknown objects in the sky, called "Russian hail" or "ghost rockets." Most were later explained as meteors.

After Kenneth Arnold’s 1947 sighting of fast-moving objects near Mount Rainier, the term "flying saucers" became popular. A Gallup poll showed 90% of Americans had heard the term, but most people didn’t know what the objects were. The idea that aliens were behind UFOs was not widely believed at first.

The Roswell incident in 1947 involved a farmer finding parts of a balloon, which the military took. In the 1950s, groups formed to study UFOs, similar to science fiction clubs. Three books published in 1950 suggested aliens might be behind UFOs, linking them to atomic bomb tests.

In 1952, a UFO scare in Washington, D.C., led to concerns about confusing real threats with UFO reports. By 1957, over 25% of Americans believed UFOs might be from space. A book by Carl Jung, a psychologist, discussed UFOs in 1959.

The U.S. Air Force studied UFOs from 1947 to 1969 through projects like Sign, Grudge, and Blue Book. They recorded 12,618 sightings. The CIA resisted making UFO records public, but some officials wanted transparency. In 1969, the Air Force stopped studying UFOs after a report said no scientific value had been found.

From the 1960s to 1990s, UFOs were part of American culture. In 1961, the Hills claimed to be abducted by aliens after seeing a UFO. Gallup surveys showed many people believed in UFOs. Some TV shows and books tried to explain UFOs as fantasy, but public interest remained strong. Sci-fi movies like Close Encounters of the Third Kind and Alien kept UFOs in the public eye.

Investigations of reports

UFOs have been studied by many groups over time, with some investigations being more detailed and scientific than others. Countries such as 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 publicly said that UFOs are real, physical objects from space or a threat to national security.

Some well-known government studies include the Swedish military's investigation of "ghost rockets" from 1946 to 1947, the U.S. Air Force's Project Blue Book (originally called Project Sign and Project Grudge) from 1947 to 1969, the U.S. Army/Air Force's secret Project Twinkle study of green fireballs from 1948 to 1951, the USAF's Special Report No. 14 by Battelle Memorial Institute, and Brazil's 1977 "Operation Saucer" (Operação Prato) by the Brazilian Air Force. France has studied UFOs since 1977 through GEPAN/SEPRA/GEIPAN within its space agency, CNES. Uruguay has also studied UFOs since 1989.

In 2008, Brazil's National Archives began receiving UFO-related documents from the Brazilian Air Force covering cases from 1952 to 2016. In Chile, the SEFAA (originally CEFAA) started collecting UFO reports in 1968, including sightings from the public, pilots, and the Chilean Air Force. This effort was led by Sergio Bravo Flores and supported by the Chilean Scientific Society. Today, SEFAA is part of the Chilean Air Force's DGAC.

In Canada, the Department of National Defence has studied UFOs and still considers some cases, like the Falcon Lake incident and the Shag Harbour UFO incident, unsolved. Early Canadian studies included Project Magnet (1950–1954) and Project Second Storey (1952–1954), supported by the Defence Research Board.

In the United States, many intelligence agencies, including the Defense Intelligence Agency (DIA), FBI, CIA, and National Security Agency (NSA), have collected UFO-related information over time. After a surge in UFO sightings in 1947, the U.S. Army Air Forces (USAAF) and FBI began a formal investigation into unexplained sightings, such as those reported by Kenneth Arnold. Scientists studied these objects to determine if they were natural phenomena or man-made. By late 1947, the Air Force concluded that the sightings were real and not imaginary.

Project Sign, created in 1947, reported that some UFOs resembled real aircraft but did not confirm their origin. In 1948, a secret report suggested UFOs might be extraterrestrial, but it was destroyed by order of the Air Force Chief of Staff. This report 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 objects that could threaten national security. The study recommended urgent action, leading to the creation of the Robertson Panel in 1953. After the panel's findings, the OS/I study ended.

Project Sign was later renamed Project Grudge in 1948 and then Project Blue Book in 1951. Ruppelt led Project Blue Book, and Hynek, a scientist, became a consultant. Hynek later criticized the lack of scientific rigor in the project and founded the Center for UFO Studies (CUFOS). 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. UFOBs were to be investigated as potential threats to U.S. security and to study their technical details.

Studies

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

Less than 10% of UFO sightings remain unexplained after proper investigation. These cases are called "unidentified" in the strictest sense. Steven Novella, a scientist, says that some people who believe UFOs are alien spacecraft often ignore simpler explanations. Instead, they suggest unusual, untested ideas that go against the scientific principle of Occam's razor, which says the simplest explanation is usually the best.

UFO research has not been widely accepted in mainstream science. Scientists generally do not consider UFO sightings important for serious study, except as a cultural topic. Most UFO studies are not published in major scientific journals. In 1969, the U.S. government stopped official UFO research after a scientist named Edward Condon said further study was not useful for science. In 2023, NASA announced for the first time that it would hire a director to study UFOs (called UAP) in a scientific and open way.

Despite government and private investigations, UFO research is not considered a real scientific field by many. Instead, it is often called pseudoscience, which means it claims to be scientific but does not follow proper scientific methods or has little evidence. Some studies say that the way UFO research is done and its relationship with science and government groups has made it hard for the public and scientists to understand UFOs properly.

Jacques Vallée, a scientist and UFO researcher, said many UFO studies have problems, including myths and beliefs that are not based on facts. He also noted that hundreds of scientists still study UFOs privately. In 2021, astronomer Avi Loeb started a project called The Galileo Project to look for signs of alien technology near Earth. In Germany, a university is working on sensors to detect and study aerial objects. A 2021 poll showed that more Americans now believe some UFOs could be alien spacecraft, rising from 33% to 41% between 2019 and 2021.

In 2022, NASA began a nine-month study to create a plan for investigating UFOs. In 2023, a study by the RAND Corporation found that UFO sightings were more common near military areas than in cities or near airports. These findings suggest that military activity might influence UFO reports.

Besides stories, UFO reports sometimes include physical evidence studied by governments, like in the U.S. Project Blue Book or in France and Uruguay. In 1998, a group of scientists reviewed UFO cases with physical evidence. A group called the Committee for Skeptical Inquiry has studied UFO claims for many years. For example, they helped show that crop circles in Indonesia were made by humans, not aliens.

Governments have studied UFOs for many years, but many stopped after concluding there was no scientific benefit. Some studies, like the U.S. Robertson Panel or the UK’s Flying Saucer Working Party, found no evidence of alien spacecraft. However, some studies, like those in Belgium and Uruguay, left open the possibility that UFOs might be real but did not prove they came from space.

In recent years, military and government officials have shared more information about UFOs, increasing public and scientific interest. For example, the U.S. Navy and Pentagon have reported sightings of unidentified objects.

In popular culture

Since the 1950s, UFOs have become a popular topic around the world. Gallup Polls show that UFOs are among the most widely recognized subjects. In 1973, a survey found that 95% of people had heard of UFOs. In 1977, only 92% had heard of U.S. President Gerald Ford, even though he had left the White House just nine months earlier. 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% of people thought aliens had visited Earth, 56% believed UFOs were real spacecraft, and 70% felt the government was not sharing all it knew about UFOs or extraterrestrial life.

The image of flying saucers has appeared in science fiction and other popular culture. Examples include the C57D in the movie 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 surrounding the Nevada base called Area 51 has made it a common topic in conspiracy theories and a lasting part of UFO culture. In July 2019, more than a million people joined a satirical Facebook event planning to "storm" Area 51, and nearly a million more said they were interested. Two music festivals, "AlienStock" and "Storm Area 51 Basecamp," were later created to take advantage of the event's popularity. About 150 people reached the entrance to Area 51, and 1,500 attended the festivals.