{Technical details below) Ralph Nelson, my father, contributed a term to the English language, from his experience in the Air Corps in WWII. When Rod Serling asked my father for a title for a new spooky show he wanted to create, my father suggested this phrase "the twilight zone" from his pilot training. DETAILS: I thank my brother, Ralph B. Nelson, for finding how it actually worked. It was a system for pilot navigation in the USA called the "Adcock Range", of many transmitters around the USA. The twilight zone was "a portion of the overlapping area of a beam where the continuous monotone "on-course" signal became temporarily overlayed with the "A" or "N" code signals." - From http://www.aerofiles.com/glossary.html