Vulcan Has No Moon

Space is big. Space is very, very big. Because space is big, objects are usually very far apart. But empty skies and vast lanes of the void of space are not aesthetically pleasing. This trope is in effect when objects in space are visible in locations where they make no sense, either due to the science or due to pre-established canon.

Related Tropes: Asteroid Thicket, Sci-Fi Writers Have No Sense of Scale. Subtrope of Space Does Not Work That Way.

Anime

 * In Robotech/Macross the Zentradi destroy an object after the SDF-1 leaves Mars orbit but before reaching Earth. Despite the fact that there aren't even asteroids between Earth and Mars in regular orbits the object is very clearly spherical making it at the very least a Dwarf Planet (and we've certainly accounted for all those). In the dub Lisa refers to it as the planet Palomir ... Okey dokey then.
 * In Aria, Mars Aqua's moons are shown as two spheres in the sky. In reality, Mars's moons are extremely tiny, and aren't even remotely spherical. At least the animators got the orbital information right. (Mind you, the moons we are shown might not be Phobos and Deimos; the setting includes celestial engineering sufficient to cover almost all of Mars with water.)

Comic Books

 * In Cry for Justice, Green Lantern and Green Arrow fly through an asteroid thicket, despite the fact that they traveled from Earth orbit to the surface, where logically there should be no asteroids.
 * There was once a Donald Duck comic where Earth appeared improbably big in the sky of Mars.

Film

 * Trope Namer is an early episode of Star Trek in which Spock tells Uhura the trope name in response to her flirting. In contrast, Star Trek: The Motion Picture shows a massive "moon" in the sky.
 * Justified in that it's so big, in fact, that Vulcan does not technically have a moon; Vulcan is a binary planet. This specificity is quite within Vulcan character.
 * Nevertheless, the Recut of Star Trek: The Motion Picture removed the moon specifically to fix this problem.
 * In the 2009 reboot, apparently Delta Vega is close enough for without a telescope. This ends up Handwaved as a psychic vision.
 * Unfortunately, it doesn't explain why the Enterprise decided to detour out to the edge of the galaxy (literally thousands of light-years out of their way) to during their urgent, maximum warp flight from Vulcan to Earth.
 * This assumes that the Delta Vega in the film is the same as the Delta Vega in the Original Series pilot "Where No Man Has Gone Before", which is not necessarily the case. There are other examples of two completely different planets having basically the same name (Charon from TOS: "Let That Be Your Last Battlefield" and Cheron from the Battle of Cheron mentioned in TNG: "The Defector", for example).
 * In John Carter, Mars's moons are shown as two huge spheres in the sky that are always right next to each other. In reality, Mars's moons are extremely tiny, and their orbital rates are so different—2.7 days east-to-west for Deimos, 11 hours west-to-east for Phobos—that they don't stay lined up in the sky.
 * Nevermind the fact that Phobos and Deimos aren't even remotely spherical.