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I'm currently writing a short story about astronauts exploring a seemingly barren planet, which is covered in steep mountains with large flat areas in between. They soon find themselves hunted by the inhabitants who only come out at night. These aliens have pitch black skin that has the ability to create bright lights using chemical reactions similar to bioluminescent animals on earth. They use their unique ability to hide on top of the mountains and blend in with the starry background as they hunt their prey.

Would this ability be a useful camouflage system?

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    $\begingroup$ Hiding on the tops of mountains doesn't seem very useful if you are hunting prey on the plains. Are these aliens airborne? $\endgroup$ – Lee Leon Jan 29 '18 at 8:33
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    $\begingroup$ Jut a side note: animals that hunt at night (or dusk/dawn) usually aren't black. They are in the colour of their environment, and they want to hide most of the way down from where they wait to where prey is. $\endgroup$ – Mołot Jan 29 '18 at 8:54
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    $\begingroup$ Make sure your creature has multispectral camouflage. Otherwise it will clearly show up if the astronauts use some kind of night vision goggles. $\endgroup$ – Anketam Jan 29 '18 at 11:46
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    $\begingroup$ One would have to ask, if the planet is seemingly barren, what would these inhabitants hunt without the astronauts? The whole ecology seems flawed to me. $\endgroup$ – Lee Leon Jan 29 '18 at 12:55
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    $\begingroup$ Don't try to emulate the sky. Emulate the mountains, Emulate the rock. $\endgroup$ – Drag and Drop Jan 29 '18 at 13:29
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No, this would not work

The problem is the angle at which other creatures, such as your astronauts, are looking at the creature. The far closer lights from the predator would appear to change their position far too fast for stars that are very, very far away when moving around in the vicinity of the predator.

Theoretically the predator could fool one of the astronauts if the creature could estimate how stars would look like from the victims point of view, which is quite hard.

Imagine there are clouds in the sky. The creature would have to emulate these cloud movements from the victims point of view. Depending on how the clouds move, how the predator moves and how the victim moves this view would change.

Spotting your predator might be hard for a single astronaut if you are willing to give your predator an incredible amount of empathy to know how it should look like for the victim, but it will be easily spotted by two or more astronauts. The best tactic would be to keep some space between each other. Even with a few foot difference the predator should be easy to spot.

The problem about your idea of just placing a lot of stars on its body and looking like a patch of the sky is that this patch of the sky is behaving different from the rest and once your astronauts found out what is hunting them it will be easy to keep an eye out for unusual star constellations that they haven't seen before and that seem to be changing their position from the astronaut's point of view.

To get an idea of why this would not work try painting a few white/yellow dots on your thumb, which should otherwise be painted black, and hold it in front of you, between your face and your computer screen. Open up MS Paint or any other painting program and draw a black background with a few white/yellow dots. Now move your face around, but keep the thumb at the same position. Ignoring the fact that the colours are probably off, how does this look like?

This all gets worse when your creature actually attacks. It has to fly/jump down from the mountain tops and land on the victim, but if the victim knows that they have to keep an eye on the sky they will probably see the rapidly closer coming stars. And again, even if you can fool the one creature you are attacking the ones that are for example behind it or looking back will probably realize that there is a patch of stars rapidly moving - down the mountain...

As was mentioned in the comments this effect is also called Parallax:

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

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    $\begingroup$ Another point is that when the creature won't have the night sky behind it, it'll be damn obvious (the glowing dots will be visible for miles - like hiding while wearing a bunch of glowsticks). Typically, for night camouflage (against humans), you want colors and textures similar to your surroundings. Against white snow, bright sand, grass or even a dark grey rock outcrop, a pitch-black silhouette is much easier to spot than a grey one (as long as there's some illumination, and if there isn't, color doesn't matter at all [also, why don't the astronauts have any? what about starlight etc?]) $\endgroup$ – G0BLiN Jan 29 '18 at 10:13
  • $\begingroup$ Pretty sure it can shut down the dots while moving or not high. Also there is no trivial way for two or more people to compare what they see to spot the parallax. Person moving will see it if they are looking at the beast, moving sideways and close enough. As your thumb example demostrates, distance matters with parallax. And when attacking the beast will be attacking a specific target, the position of which it knows and can adjust its light pattern to camouflage its motion. $\endgroup$ – Ville Niemi Jan 29 '18 at 11:04
  • $\begingroup$ @VilleNiemi Exactly. Shutting down the dots means that a pitch black spot is visible because the background is rocks, which won't be pitch black. And while focusing on one victim the dots may be sufficiently adapted for that one person not to see the predator, but for the person behind these dots will move in strange patterns or there will be a strange patch of pitch black before the rocky background scenery moving - because the dots are not adapted to the not-victim. For a single target this might work, but groups will easily spot the beast when it attacks. $\endgroup$ – Sec SE - clear Monica's name Jan 29 '18 at 11:23
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    $\begingroup$ how about making them flying creatures, great big wings that they hold out and whose undersides are coloured as you like. In the day they curl up on the mountains where the top of their skins are rock-coloured. It probably wouldn't fool the astronauts for very long, but you could have an atmosphere that has lots of moving points of light - micro meteorites or lots of tiny moons in orbit for example - that would help hide the creatures as they glide up in the sky. $\endgroup$ – gbjbaanb Jan 29 '18 at 16:16
  • $\begingroup$ I guess I assumed that the beasts can fly since camouflaging as a night sky does not really make sense otherwise. (And hiding on mountain tops to hunt things on the plains doesn't really work otherwise either.) But it doesn't really say that outright, does it? $\endgroup$ – Ville Niemi Jan 29 '18 at 16:55
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Secespitus's answer is good as far as the visible spectrum issues, I would like to add something on a slightly different line: astronauts on an exploration mission are not, repeat not, going to be relying on the visible spectrum for surveying a new world they're going to have, at a minimum, night vision gear with light amplification and infra-red. So unless your astronauts are criminally under resourced or criminally stupid your predator has to produce no body heat whatsoever or they are going to see it clear as day.

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  • $\begingroup$ "criminally under resourced or criminally stupid" - You mean Covenant stupid and underresourced? ;) It still earned a pretty penny, right? $\endgroup$ – Mołot Jan 29 '18 at 14:08
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    $\begingroup$ @Mołot That, Prometheus, and Red Planet were in my thoughts yes, at least the latter made some good excuses as to why all their advanced gear was unavailable/broken. $\endgroup$ – Ash Jan 29 '18 at 14:18
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It is hard to blend in with a static background if you are on the move, and a starry night sky is fairly static. But not all night skies are static.

aurora http://www.enriquepacheco.com/wp-content/uploads/2012/01/Aurora-10.jpg

If your planet has phenomenal and varying auroras every night, the creature could definitely blend with those. If you have never seen an aurora go check youtube - they are dynamic, shifting and drifting and changing color.

As regards the "seemingly barren" surface of the planet, I recommend you riff further on the camouflage theme. Perhaps your aerial hunters that look like the sky are not camouflaging themselves from their prey, but from their own terrestrial predators whose camouflage is even better.

stargazer fish source

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