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Many science fiction movies involve scenes set on the surface of alien planets. In many of these scenes we see objects in the sky of the alien planet; sometimes a sun or suns; more often one or more alien moons. These objects are almost always very large compared to any standard of realistic physics.

The earth has a very large moon by known standards. It occupies an angle of about 0.5 degrees in the sky. It is, relative to the earth, the biggest moon in the solar system (and the biggest satellite we know). What we see in the sky on earth is therefore very large for a satellite.

But there are SciFi movies where we see alien skyscpaes with huge moons relative to the visual size of Earth's moon (which is very large).

And this is hardly a new thing. This is from Star Trek TOS:

Star Trek TOS image

This is from Total Recall:

Total Recall 1990 image (note that in this case we know how big the moon's of Mars are and it would be surprising if they can be seen at all from the surface: they are tiny).

This (the one that finally prompted me to ask this question) is from Altered Carbon and is a scene from Harlan's World:

Harlans World skyscape

Is there any good reason why SciFi moons are so big? Or is this a case of "I don't care about the laws of physics as long as it looks good on screen"?

Is there any in-universe justification for this common trope?

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    You're looking for an in-universe justification? Of what universe actually?
    – Napoleon Wilson
    Jun 8, 2018 at 8:56
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    @matt_black the scene from TOS is actually from TOS-R, replacing a scene from TOS "The Cage" and "Requiem for Methuselah" that also showed a very large moon. Deimos has about 1/19th the apparent diameter of Earth's moon and appears star like from Mars's surface, while Phobos has about a third the apparent diameter of Earth's moon. They are clearly visible from Mars's surface. Jun 8, 2018 at 19:47
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    I think that on the average most habitable planets will have either no moons or moons that look much smaller than Earth's moon. But some will have moons large and/or close enough to look much larger than Earth's moon. No doubt movie makers always choose those rare planets to set their films on. And filming through a telephoto lens can make Earth's moon or alien moons seem much larger than they are. Jun 9, 2018 at 17:22
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    The pictures you've shown have them relatively close to the horizon. It's a well known optical illusion that moons look larger there.
    – nitind
    Jun 12, 2018 at 4:08
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    The Total Recall image may not be the best example, given that Quaid is only an ordinary guy having an implanted fantasy about traveling to Mars. :-) Jun 29, 2018 at 16:44

3 Answers 3

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This is both an aesthetic choice, and a narrative strategy, utilized to emphasize the "alien-ness" of these speculative worlds. Similar strategy to utilizing multiple moons.

For my money, the original Starwars is still the exemplar (pre-digital, y'all):

double sunset on Tatooine

Here it's not the size of the celestial bodies, but the dual objects--Lucas is able to convey an absolutely convincing reality of the setting with physical props and real location, but the two suns that tell us this ain't earth.

  • It's a form of visual shorthand to reinforce the alien-ness of these locations

also:

  • Large moons are aesthetically appealing

ET and that kid flying in front of the moon

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    Those are the two suns of Tatooine. Not moons. Jun 28, 2018 at 20:55
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    @WakeDemons3 I acknowledge that they are suns, but the answer to the OP's question is not literal, and in no way confined to large moons. (i.e. we're talking about the symbolism, aka visual cues, used to convey narrative qualities of an alien location.)
    – DukeZhou
    Jun 28, 2018 at 21:04
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I'm going to shadow DukeZhou's answer and concentrate on one aspect of it; it's a visual cue that the characters aren't on Earth. Sometimes it's a large moon, sometimes it's multiple moons, sometimes it's a large planet visible in the daytime sky... No matter what the cue, it's something you wouldn't see on Earth and thus let's you know this definitely isn't taking place on our planet. It lends more credence to being filmed on a different planet. As for what that visual is, that's entirely up to the creative staff and what they think fits in with the world they're creating.

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It is whether the smaller or medium moons orbit are far or near in one planet, then that would make the view in the alien sky making the moons smaller or bigger. some sci-fi shows in another planet shows some exoplanets or random alien moons like larger or smaller depending on what the moons or planet are orbiting (Like larger gas giants or small/medium moons orbiting one large planet, far distance or near distance orbit)

For Example If The Kilometer Size Of The Moon Is Like 3,700 while the orbit is far in the planet's view then the view in naked would make it smaller. That is how the director or the creator of the movies would think of it.

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  • By The Way, I Hope This Helps! :D Jan 7 at 9:19
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    I'm sorry but this makes no sense to me. You may want to re-read and rewrite it a little.
    – iandotkelly
    Jan 7 at 14:25

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