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. 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. 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. 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.
UFOs have become a prominent theme in modern culture, and this cultural phenomenon has been the subject of academic research.
