Other terms are self-explanatory. Daylight discs, another expression from ufological jargon, are objects, apparently metallic, apparently structured, and obviously disc-shaped, which are observed between dawn and dusk. Nocturnal lights are what people report at other times of the day. Nocturnal lights are the kinds of ostensible UFOs that investigation is most likely to turn into IFOs- identified flying objects, the sorts of mundane stimuli (airplanes, planets, stars, meteors, weather balloons, satellite debris, and the like) that people mistake for something more interesting. Nonetheless genuinely anomalous nocturnal lights, often performing fantastic aerial gymnastics, have been reported on numerous occasions. Radar/ visual cases are those, of course, in which UFOs are picked up on radar and seen by the eye.
In his book The UFO Experience (1972) the late Dr. J. Alien Hynek devised a classification scheme for close encounters. Despite occasional efforts to change or modify it, the categories have been accepted by virtually all ufologists and UFO writers, including this one:
Close encounters of the first kind (CE1s): the appearance of a UFO within 500 feet or less of the witness.
Close encounters of the second kind (CE2s): incidents in which a UFO affects the environment in some way, for example by scorching vegetation, leaving landing traces, burning or otherwise injuring witnesses. In a CE2, in Hynek's words, a UFO has a "measurable physical effect on either animate or inanimate matter."
Close encounters of the third kind (CE3s): reports of beings, usually humanoid, in connection with UFO sightings. One subset of CE3s is the abduction experience, in which persons allegedly are taken against their will into UFOs and subjected by their humanoid occupants to physical tests or experiments before they are released, in two cases out of three with some sort of memory impairment; memory may return later through hypnotic regression or spontaneous recall. A few writers have sought to put these latter cases into a close-encounter category of their own, "close encounters of the fourth kind," but this idea has failed to catch on, probably because it is neither helpful nor necessary. In fact (or, more specifically, in allegation), the dividing line between CE3s and "CE4s" is vague at best, since many cases once thought to be traditional CE3s, in which witnesses reported occupants but no abduction, later turned out to be abduction cases. The famous story of Barney and Betty Hill, the New Hampshire couple whose supposed kidnapping by extraterrestrials became the subject of a best-selling book and a popular television movie, was known to ufologists as a typical CE3 for the first four years of its existence. Only when the Hills underwent hypnotic regression with Boston psychiatrist Benjamin Simon did the abduction aspect emerge. Moreover, the beings who figure in abduction stories and nonabduction CE3s are generally alike. There is, in short, no radical discontinuity between the CE3 and the abduction; the latter seems but one kind of the former.
A radical discontinuity does exist, however, between CE3s and contactee experiences. Contactees are individuals who claim to be in frequent communication with wise, beautiful, godlike beings from other worlds here to save earthlings from destroying themselves. These contacts may take place physically or (far more frequently) psychically. Contactees tend to be individuals with a long history of involvement in occultism and metaphysics. Unlike the overwhelming majority of UFO witnesses, including CE3 percipients, who have no prior interest in UFOs, anomalies or the paranormal, contactees have in some sense waited all their lives for word from the Space Brothers, as such beings are usually called in the contactee literature. The occupants who figure in CE3s do not look or act like this; they are usually small, grotesque-looking and minimally communicative. Contact claims represent a visionary religious response to the UFO phenomenon; in them older occult doctrines are wrapped in Space Age garb. Although fraudulent contactees do exist, the typical contactee is sincerely convinced of the reality of his interactions with otherworlders. But such interactions are nearly always ones that cannot be shared. Although there are many multiple-witness CE3s, multiple-witness cases among contactees not engaged in outright hoaxing are virtually nonexistent, suggesting subjective rather than objective causes.