In his 1972 book The UFO Experience: A Scientific Study, renowned UFO expert Dr. J. Allen Hynek came up with a taxonomy for UFO
sightings based on the nature of a given sighting, the observer's distance or its impact. Though it was superseded later by the more detailed
Vallee Classification System, created by his disciple Dr. Jacques Vallee, it is still used as a basic guide for classifying UFO sightings.
- Nocturnal Light
- Visual sighting of a light in the night-time sky. This accounts for up to 40% of all UFO sightings.
- Nocturnal Disc
- A distinction added to the Hynek system at a later time. This is a Nocturnal Light with a discernible structure or shape.
- Daylight Disc
- A UFO with a distinct shape observed in daylight
- Radar Case
- Unknown object(s) detected by radar
- Radar Visual Case
- Object(s) simultaneously observed visually and by radar. No more than 2% of the total, these are the more inexplicable cases.
Close encounters are characterised by the observer's distance being no more than 500' (150m) from the unidentified object. The
difference is generally measured by the impact on the observer and/or the surroundings.
- First kind
- Simple sighting of a UFO
- Second kind
- UFO leaves evidence such as burn marks or fragments of unknown material
- Third kind (the famous sort)
- Visual contact with UFO occupants
- Fourth kind (not expressly approved by Hynek but used anyway)
- Abduction of the human subject
- Fifth kind (added later)
- There are two different opinions here
- Vallee holds it to be injury or death as a result of the encounter
- Dr. Steven Greer considers it to be communication between a human and an alien
Sources (information is widely available):
The Temporal Doorway
Alien Abduction Experience and Research