The UFO Experience: A Scientific Inquiry

The UFO Experience (Regnery, 1972) is the first book by J. Allen Hynek, the Northwestern University astronomer who served as the Air Force's scientific consultant on UFOs for more than twenty years, through Projects Sign, Grudge and Blue Book. Written after Blue Book closed in 1969, it argues that a residue of well-reported cases deserves serious scientific study, and criticises the Air Force project and the Condon Report for failing to give it that.

The book introduced Hynek's classification of reports: nocturnal lights, daylight discs and radar-visual cases, and "close encounters" of the first, second and third kinds. The scale passed into popular culture through Spielberg's 1977 film, on which Hynek consulted and briefly appears. Hynek admitted that he had begun as a debunker for the Air Force; sceptics such as Robert Sheaffer, who previewed a chapter in 1970, argued that his later work was too ready to accept poor evidence.

Sources: Wikipedia · J. Allen Hynek's file