Later in 1967, physicist John Archibald Wheeler would popularize the term "black hole" to refer to the phenomenon Kirk describes as a black star, at the suggestion of a student. While several sources credit Wheeler for coining the phrase, it was used in science journals as early as 1963. The term is now credited to physicist Robert H. Dicke, comparing the phenomenon to a life prison dungeon in Calcutta known as the "Black Hole of Calcutta".
Captain Kirk says the first moon shot was in the late 1960s. This was the first prediction of the correct decade of this accomplishment in a major science fiction work. Previous motion pictures and television series put the first lunar mission sometime in the 1970s at the earliest.
Captain Christopher is given the tunic of a full lieutenant, the naval equivalent of his Air Force captain rank.
The episode originated from a one-page story synopsis associate producer Robert H. Justman submitted to Gene Roddenberry on 12 April 1966, for possible consideration. Although almost beat for beat, Justman's proposed story is the same as this episode, Roddenberry never acknowledged Justman as the source or paid any royalties to him for the idea.
The Enterprise crew intercepts a radio report that the first manned moon shot will take place on Wednesday. Apollo 11 was launched nearly two years after the filming on 16 July 1969, a Wednesday.