Hynek system

Dr. J. Allen Hynek developed another commonly used system of description, dividing sightings into six categories. It first separates sightings based on proximity, arbitrarily using 500 feet as the cutoff point. It then subdivides these into divisions based on viewing conditions or special features. The three distant sighting categories are:

* Nocturnal Lights (NL): Anomalous lights seen in the night sky.
* Daylight Discs (DD): Any anomalous object, generally but not necessarily "discoidal", seen in the distant daytime sky.
* Radar/Visual cases (RV). Objects seen simultaneously by eye and on radar.

The distant classification is useful in terms of evidentiary value, with RV cases usually considered to be the highest because of radar corroboration and NL cases the lowest because of the ease in which lights seen at night are often confused with prosaic phenomena such as meteors, bright stars, or airplanes. RV reports are also fewest in number, while NL are largest.

In addition were three "close encounter" (CE) subcategories, again thought to be higher in evidentiary value, because it includes measurable physical effects and the objects seen up close are less likely to be the result of misperception. As in RV cases, these tend to be relatively rare:

* CE1: Strange objects seen nearby but without physical interaction with the environment.
* CE2: A CE1 case but creating physical evidence or causing electromagnetic interference (see below).
* CE3: CE1 or CE2 cases where "occupants" or entities are seen. (Hence the title of Steven Spielberg's movie, Close Encounters of the Third Kind)


Hynek's CE classification system has since been expanded to include such things as alleged alien abductions (CE4s) and cattle mutilation phenomena.