A Field Guide to UFO and Close Encounter Classification

For most of the subject's history, "UFO" meant too many things at once. A light in the night sky and a craft on the ground were both called UFOs, and the difference between them — the difference that matters most — was lost in the one word. The classification that gives the field its vocabulary was the work of one astronomer trying to sort that out.

J. Allen Hynek

J. Allen Hynek was an astronomer who began as a consultant to Project Blue Book, tasked with giving astronomical explanations for sightings. Over the years he came to believe the subject deserved better than it was getting, and in 1972 he published The UFO Experience, which proposed a system for sorting reports by how close the encounter was. The system is still used.

The three distance categories

Hynek first sorted reports by the conditions of observation:

• Nocturnal lights — lights seen at night, with no detail discernible. The largest category, and the hardest to interpret.
• Daylight discs — objects seen in daylight, with shape and detail visible. Far fewer of these, and correspondingly more informative.
• Radar-visual cases — objects detected on radar and seen visually at the same time. The rarest, and the kind the archive weights most heavily; the 1952 Washington, D.C. incidents and the JAL 1628 case both fall here.

Close encounters of the first kind (CE1)

A close encounter, in Hynek's system, begins when the object is close enough to leave detail beyond a point of light. A CE1 is a sighting within roughly 150 meters, with enough detail to describe shape, surface, or behavior, but with no physical effect on the surroundings or the witness.

Close encounters of the second kind (CE2)

A CE2 adds a physical effect. The object leaves a trace: a mark on the ground, interference with a vehicle's electrics, a measurable effect on a person, an animal reacting. The Rendlesham clearing's reported depressions and radiation readings, for instance, sit in this category. A CE2 is not more "true" than a CE1; it is more examinable, because it left something behind.

Close encounters of the third kind (CE3)

A CE3 is a close encounter in which beings are reported present — occupants, entities, figures. The Betty and Barney Hill account and the Ariel School reports are CE3 cases. Hynek himself was cautious about this category, and the archive keeps the same caution: a CE3 is a report of beings, which is not the same as the presence of beings.

Extensions and limits

Later writers added a fourth, fifth, and sixth kind — abductions, contact, and beyond — but these were added by others after Hynek, and are not part of his original system. The archive uses Hynek's three close-encounter categories and notes the later ones as extensions rather than established taxonomy.

The classification's great strength is also its limit. It describes how close the encounter was, not what the object was. A CE2 is a report with a physical trace; it is not a verdict that the trace was left by an extraordinary object. The system sorts the record. It does not settle it.

For how the archive reads the records this system describes, see The Alien Archives Guide to Reading a UFO Case File.