- 1.1 Nocturnal Lights
- 1.2 Daylight Discs
- 1.3 Radar-Visual
- 1.4 Close Encounters of the First kind
- 1.5 Close Encounters of the Second kind
- 1.6 Close Encounters of the Third kind
Hynek devised a sixfold classification for UFO sightings: They are arranged according to increasing proximity.
NL: Nocturnal Lights. Lights in the night sky.
DD: Daylight Discs. UFOs seen in the daytime, generally having discoidal or oval shapes.
RV: Radar-Visual. UFO reports that have radar confirmation. These seem to offer harder evidence that the objects are real, although radar propagation can often be unreliable
CE1: Close Encounters of the First kind. Visual sightings of an unidentified flying object seemingly less than 500 feet away that show an appreciable angular extension and considerable detail.
CE2: 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.
CE3: Close Encounters of the Third kind. UFO encounters in which an animated creature is present. These include humanoids, robots, and humans who seem to be occupants or pilots of a UFO.