BTW: In Hynek's book, "The UFO Experience: A Scientific Inquiry", there were 4 chapters that (IMO) were the better parts, Close encounters of the first kind, Close encounters of the second kind, Close encounters of the third kind, and Close encounters of the forth kind..
This is where the title of the movie came from...
Heh... I knew that... and Hynek was hired as technical advisor on the film.