In ufology, a close encounter is an event in which a person witnesses an unidentified flying object. This terminology and the system of classification behind it were first suggested in astronomer and UFO researcher J. Allen Hynek's 1972 book The UFO Experience: A Scientific Inquiry. Categories beyond Hynek's original three have been added by others but have not gained universal acceptance, mainly because they lack the scientific rigor that Hynek aimed to bring to ufology. Sightings more than from the witness are classified as "Daylight Discs," "Nocturnal Lights," or "Radar/Visual Reports." Sightings within about are subclassified as various types of "close encounters." Hynek and others argued that a claimed close encounter must occur within about to greatly reduce or eliminate the possibility of misidentifying conventional aircraft or other known phenomena. Hynek's scale became well known after being referenced in a 1977 film, Close Encounters of the Third Kind, which is named after the third level of the scale. Promotional posters for the film featured the three levels of the scale, and Hynek himself makes a cameo appearance near the end of the film.
Hynek's scale
Hynek devised a sixfold classification for UFO sightings: They are arranged according to increasing proximity:
UFOs seen in the daytime, generally having discoidal or oval shapes
Radar-Visual
UFO reports that have radar confirmation—these supposedly try to offer harder evidence that the objects are real, although radar propagation can be occasionally discredited due to atmospheric propagation anomalies
Close Encounters of the First Kind
Visual sightings of an unidentified flying object, seemingly less than away, that show an appreciable angular extension and considerable detail
Close Encounters of the Second Kind
A UFO event in which a physical effect is alleged; this can be interference in the functioning of a vehicle or electronic device, animals reacting, a physiological effect such as paralysis or heat and discomfort in the witness, or some physical trace like impressions in the ground, scorched or otherwise affected vegetation, or a chemical trace
Close Encounters of the Third Kind
UFO encounters in which an animated entity is present—these include humanoids, robots, and humans who seem to be occupants or pilots of a UFO
A Close Encounter of the Fourth Kind is a UFO event in which a human is abducted by a UFO or its occupants. This type was not included in Hynek's original close encounters scale. Hynek's erstwhile associate Jacques Vallee argued in the Journal of Scientific Exploration that the "Fourth Kind" should refer to "cases when witnesses experienced a transformation of their sense of reality", so as to also include non-abduction cases where absurd, hallucinatory or dreamlike events are associated with UFO encounters. The film The Fourth Kind makes reference to this category.
Close Encounters of the Fifth Kind
A Close Encounter of the Fifth Kind is a UFO event that involves direct communication between aliens and humans. This type of close encounter was named by Steven M. Greer's CSETI group and is described as bilateral contact experiences through conscious, voluntary, and proactive human-initiated cooperative communication with extraterrestrial intelligence.
Close Encounters of the Sixth Kind
Death of a human or animal associated with a UFO sighting
