UFO Guide

A Brief Guide to UFOs

What is a UFO?

An unidentified flying object (UFO), in its strictest sense, is an unfamiliar anomaly in the sky that is not readily identifiable to the observer as any known object. [i] Technically, 'UFO' refers to something that cannot be identified; unfortunately, in contemporary popular culture, the term has become synonymous with extraterrestrial spacecraft. However, decades of investigations, research, and analysis from a cadre of UFO investigators, including the United States Air Force and the British Ministry of Defence, have established that most UFO sightings are either hoaxes or misidentifications of man-made terrestrial objects and natural phenomena. [ii] Evidence of extraterrestrial life remains as elusive as ever.

UFO Study

Studies have established that the majority of UFO observations are misidentified conventional objects or natural phenomena – most commonly aircraft, balloons, noctilucent clouds, nacreous clouds, or astronomical objects such as meteors or bright planets, with a small percentage even being hoaxes. After excluding incorrect reports, however, most investigators have acknowledged that between 5% and 10% of reported sightings remain unexplained, and therefore can be classified as unidentified in the strictest sense. Many reports have been made by trained observers such as pilots, police, and the military; some have involved simultaneous radar tracking and visual accounts. Proponents of the extraterrestrial hypothesis suggest that these unexplained 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 although some scientists support the extraterrestrial hypothesis, few scientific papers about UFOs have been published in peer-reviewed journals. There remains some debate in the scientific community about whether any scientific investigation into UFO sightings is warranted.

UFO Terminology

The first reports of sightings typically referred to mystery airships. When reported, they were so described during the latter part of the 19th century and the early 20th. Later, during World War Two, the term 'foo fighters' was used by American fighter pilots who reported encounters with UFOs. The first widely publicised sighting, reported over the USA by private pilot Kenneth Arnold, in June 1947, gave rise to the popular terms 'flying saucer' and 'flying disc', of which the former is still sometimes used (even though Arnold said that most of the objects he saw were not exactly circular and that one was actually crescent-shaped). In addition, the infamous Roswell UFO Incident occurred at about the same time, further fueling public interest. The term 'UFO' was first suggested in 1952 by Capt. Edward J. Ruppelt, who headed 'Project Blue Book', then the USAF’s official investigation of UFOs. Ruppelt felt that 'flying saucer' did not reflect the diversity of the sightings. He suggested that UFO should be pronounced as a single word ('you-foe'). However, it is now usually pronounced by forming each letter: U.F.O. Because the term is ambiguous, referring either to any unidentified sighting, or in popular usage to alien spacecraft, and because of the public and media ridicule sometimes associated with the topic, some investigators prefer to use such terms as 'unidentified aerial phenomenon' (UAP) or 'anomalous phenomena', as in the title of the National Aviation Reporting Center on Anomalous Phenomena (NARCAP) in America. The equivalent acronym for UFO in Spanish, Portuguese, French, and Italian is OVNI ('Objeto Volador No Identificado', 'Objeto Voador Não Identificado', 'Objet Volant Non Identifié' or 'Oggetto Volante Non Identificato'), pronounced as one word ('ov-nee').

UFO Hypotheses

For the sightings that remain truely unexplained, a number of hypotheses - or theories - have been suggested over the years; including (but not limited to): [iii]

(a) The "Extraterrestrial" Hypothesis (ETH) - suggesting that (true) UFOs could be (piloted or automated) spacecraft from other planets and solar systems.

(b) The "Time Traveller" Hypothesis (TTH) - suggesting that (true) UFOs could be craft from our own future travelling back through time.

(c) The "Alternate Universe" Hypothesis (AUH) - suggesting that (true) UFOs could be craft from an alternate Universe, itself part of a larger "Multiverse".

(d) The "Living Organism" Hypothesis (LOH) - suggesting that (true) UFOs could, themselves, be biological, living creatures.

(e) The "Paranormal Phenomena" Hypothesis (PPH) - suggesting that (true) UFOs could be something paranormal or supernatural (e.g. "ghosts").

(f) The "Hollow Earth" Hypothesis (HEH) - suggesting that (true) UFOs could be craft from civilisations living inside planet Earth.

UFO Classification

Today's UFO researchers have Jacques F. Vallée and J. Allen Hynek to thank for the development of systems used to classify UFO sightings. [iv] It is believed the first classification system was developed by French scientist, Vallée (along with Aimé Michel and Dr. Pierre Guérin) in the early 1960s. This provided 4 categories of classification in which to place the numerous UFO reports being received at the time.

In the early 1970s, following joint projects with Vallée, the American, J. Allen Hynek, proposed a system that built upon the earlier one and split sightings into 6 categories (Nocturnal Lights, Daylight Discs and Radar-Visual for distant sightings and the familiar Close Encounters categories 1-3 for close-by events). This system, along with the addition of a later CE-4 category, is still used today by some researchers.

A further development in UFO classifications followed when Jacques F. Vallée produced a 20-category system to better register and record the behaviour of the UFO seen (shown right or below, depending on the size of your viewing device).


[i] Sagan, Carl & Page, Thornton. “Definition of a UFO” UFOs: A Scientific Debate, 1995

[ii] United States Air Force. Project Blue Book, 1947-1969

[iii] Moore, Robert. The Ufology Handbook, 2013

[iv] Vallée, Jacques F. A System of Classification and Reliability Indicators for the Analysis of the Behavior of Unidentified Aerial Phenomena, 2007

Original Article: Antonio Paris, Director, Aerial Phenomenon Investigations (API). [Article Additions: British Ufology]

Images: Joen Asmussen (free distribution) and Jacques F. Vallée