- Nocturnal lights: the witness observes unexplained lights in the sky during the night from a distance more than 500 feet (150 meters).
- Daylight discs: the witness observes a distant U.F.O. (more often with a round shape).
- Radar-visual: The previous observation is at the same time visual and radar.
- Close encounter of the first kind: observation of an U.F.O. at a distance less than 500 feet (150 meters).
- Close encounter of the second kind: the observed U.F.O. leaves material proof (ground tracks, radiations…)
- Close encounter of the third kind: direct observation of the U.F.O. and its occupiers.
The Hynek’s scale was extended:
- Close encounter of the fourth kind: kidnapping of the witness by the U.F.O.’s occupiers.
- Close encounter of the fifth kind: communication the U.F.O.’s occupiers.
- Close encounter of the sixth kind: death (accidental or not) due to an U.F.O. and/or its occupiers.
- Close encounter of the seventh kind: creation of an alien/human hybrid, by sexual reproduction or by scientific method.
- Close Encounter of the Third Kind, directed by Steven Spielberg
- The end of Star Trek: First Contact, directed by Jonathan Frakes