In 1972, astronomer J. Allen Hynek proposed that there are three types of close encounters that humans can have with beings that we would refer to as extraterrestrial in his book, The UFO Experience: A Scientific Inquiry. The aim of Hynek’s work was not to endorse or dismiss the possibility of life that existed beyond the knowledge of humans somewhere in our, or a neighboring universe, so much as to explore what possibilities are out there, and how to categorize any reported contacts. His goal was to get researchers, and regular people, moving beyond superstition, panic, and outright absurdity in some cases, and thinking in a more rational and objective manner.
In doing so, Hynek outlined close encounters of the first through third kind. Over the years, many people have taken those three types of encounters and expanded them into a number of subcategories, and even an extended list which outlines 7 different categories of close encounters. Few, if any, of the 4 newer categories of encounters are widely accepted. In fact, not even Hynek accepts them as rational. Hynek, for his part, was not even enthusiastic about including a close encounter of the third kind on his original list. While there are literally over 100 different types of encounters that have been outlined in subheads and add-ons to the seven kinds of close encounters most commonly discussed, it is only the seven that will be explained here.
A close encounter of the first kind is a sighting in which one or more unidentified flying objects have been spotted. This would include objects loosely described as flying saucers, objects which can not be attributed to known human technology that appear in the sky, or strange lights for which no rational explanation can be offered. Close encounters of the first kind are the most commonly reported events on the Hynek scale.
A close encounter of the second kind is one in which a UFO has been spotted, but there is associated phenomena that accompanies it. The phenomena can be a crop circle, terrain damage, scared animals, electronic or mechanical interference, gaps in memory (lost time), heat or radiation, catalepsy (paralysis), or some form of unnatural physical occurrence.
Close encounters of the third kind would be those in which a UFO has been spotted, but go further to include a visual confirmation of an animate object that is associated to the UFO. For many years, reports of a close encounter of the third kind were the most controversial as there is little to no way to prove their validity.
A close encounter of the fourth kind is one in which a human is abducted by an extraterrestrial. In some cases depending on the many interpretations of this, abduction does include a visitation in which the human is not actually taken aboard a UFO, but is in the custody of an ET while still on Earth.
A close encounter of the fifth kind is one in which there is bilateral contact with an extraterrestrial entity. This can be through some audible form of communication, or by some form of mental/telepathic communication. The contact can be initiated by either a human or extraterrestrial.
A close encounter of the sixth kind entails a UFO or its inhabitants directly causing injury or death. It has been cited numerous times that this is unnecessary as it is already included on the Hynek scale under physical contact.
The most controversial encounter to most is a close encounter of the seventh kind. A close encounter of the seventh kind is one in which a human and extraterrestrial mate to produce a hybrid being. This is hardly a new theory, it actually dates back to the ancient Egyptians according to some translations of ancient texts, but it is still often seen as a bit too hard to conceive as possible in many regards from a biological sense.
This has been outlined for informational purposes, not to endorse or invalidate any beliefs. Over the years, many kinds of encounters have been slightly changed, not all sources agree on what are the actual kinds of close encounters beyond those of the fourth kind. While science itself seems to only endorse the possibility of extraterrestrial intelligence, at this time, encounters beyond the second kind have not received any accepted empirical investigation that has been made public.