A system commonly used to classify sightings of Unidentified Flying Objects that was developed by UFOlogist J. Allen Hynek. The system categorises experiences with UFOs and possible extraterrestrial entities on a scale of 'close encounters', the higher the degree of close encounter the more interaction there is. Hynek originally proposed three types of close encounter however additional ones were later added unofficially by other researchers but that are not generally recognised in the field.
