|Affiliation:||United Federation of Planets|
Delta IV was an inhabited planet. This planet was the homeworld for the Deltans, a warp capable humanoid species. It was the fourth planet in the Delta planetary system. (Star Trek: The Motion Picture; Star Trek IV: The Voyage Home)
In the writers/directors guide for Star Trek: Phase II, the Deltan homeworld was referred to as 114-Delta V. The same document also stated that the planet had "recently joined the Federation." (Star Trek Phase II: The Lost Series, p. 90) In the first-draft script for "In Thy Image" (the story that gradually transformed into The Motion Picture – the script was dated 20 October 1977), the Deltan homeworld was referred to as Delta 14. (Star Trek Phase II: The Lost Series, pp. 121 & 139)
In November 1977, consultant company De Forest Research addressed the naming of the Deltan homeworld, stating that the word "Delta" being used as a planet name presents a problem in astronomy, since it (in common with other Greek letters) is commonly used to identify a particular star in a generic, recognized constellation. "That it would ever be used as a planetary name is very unlikely," the research company declared. They concluded, "We would be happy to consult on other possibilities which might be more in accord with standard astronomical usage." (Star Trek Phase II: The Lost Series, p. 64)
Evidently, the production crew did not adhere to the advice from De Forest Research, and variations of the name were included in several examples of documentation that were much more closely related to The Motion Picture than they were to Phase II. In a character study of Ilia that Gene Roddenberry wrote for the film, the Deltan homeworld was referred to as Delta. (The Making of Star Trek: The Motion Picture, p. 108) The planet was also mentioned in notes that costume designer Robert Fletcher wrote, regarding the various aliens in the movie. In that case, the Deltan homeworld was called "Planet Delta 4." (The Making of Star Trek: The Motion Picture, p. 133)
According to The Worlds of the Federation (page 64), Delta was the fifth planet orbiting Delta Triciatu, a white dwarf star. The indigenous name for the planet Delta was Seyalia. It had two moons Seyann and Cinera. The planet was covered by vast forests. According to Star Trek: Star Charts ("United Federation of Planets I"), The Delta system was a single star system. The star Delta was a F class star with a magnitude of +5, which was the same brightness as Sol. Delta IV was a Federation member in 2378.