A purported 1952 photo of a UFO over Passaic, New Jersey, from an FBI document

"UFO" redirects here. For other uses, see UFO (disambiguation).
A UFO or Unidentified Flying Object is any real or apparent flying object which cannot be identified by the observer and which remains unidentified after investigation.

Sightings of unusual aerial phenomena date back to ancient times, but reports of UFO sightings started becoming more common after the first widely publicized U.S. sighting in 1947. Many tens of thousands of such claimed observations have since been reported worldwide, and it is very likely many more go unreported due to fear of public ridicule because of the social stigma created around the UFO topic.

In popular culture throughout the world, UFO is commonly used to refer to any hypothetical alien spacecraft but the term flying saucer is also regularly used. Once a UFO is identified as a known object (for example an aircraft or weather balloon), it ceases to be a UFO and becomes an identified object. In such cases it is inaccurate to continue to use the acronym UFO to describe the object.

UFOs in popular culture
Beginning in the 1950s, UFO-related spiritual sects, sometimes referred to as contactee cults, began to appear. Most often the members of these sects rallied around a central individual, who claimed to either have made personal contact with space-beings, or claimed to be in telepathic contact with them. Prominent among such individuals was George Adamski, who claimed to have met a tall, blond-haired Venusian named “Orthon,” who came to warn us about the dangers of nuclear proliferation. Adamski was widely dismissed, but an Adamski Foundation still exists, publishing and selling Adamski’s writings. At least two of these sects developed a substantial number of adherents, most notably The Aetherius Society, founded by British mystic George King in 1956, and the Unarius Foundation, established by “Ernest L.” and Ruth Norman in 1954. A standard theme of the alleged messages from outer-space beings to these cults was a warning about the dangers of nuclear proliferation. More recent groups organized around an extraterrestrial theme include Ummo, Heaven’s Gate, Ra?l, and the Ashtar Galactic Command. Many of the early UFO sects, as well as later ones, share a tendency to incorporate ideas from both Christianity and various eastern religions, “hybridizing” these with ideas pertaining to extraterrestrials and their benevolent concern with the people of Earth.