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Knowledge Base / Hynek Classification System

In 1972, Dr. Allen J. Hynek published The UFO Experience: A Scientific Study, laying the groundwork for serious scientific study of UFOs. The book contained one of the most famous and important contributions to UFOlogy, the Hynek Classification System. This system provided a way to categorize or group UFO sightings, and is famous among the general population for coining the phrase "close encounters."

The Hynek Classification System categorizes UFO sightings as either "distant sightings" or "close encounters."

  • Nocturnal Light – A light seen in the sky at night.
  • Daylight Disk – An unidentified object seen in the daytime (not necessarily disk-shaped).
  • Radar-Visual – An object seen on radar that is verified by a visual observation.

  • Close Encounter of the First Kind – A UFO seen at close range, but with no interaction with the environment.
  • Close Encounter of the Second Kind – A UFO seen at close range, and physical traces or interaction with animals or objects are noted.
  • Close Encounter of the Third Kind – A UFO seen at close range, and occupants are noted.
Since Dr. Hynek's death in 1986, the UFOlogy community has added two new classes of close encounters:
  • Close Encounter of the Fourth Kind – Alien abduction.
  • Close Encounter of the Fifth Kind – Establishes communication between human and alien.