How does one hide a floating island in the sky from anyone below looking up?

Question

So, floating islands are a pretty common trope at least in the media I've consumed, and one thing that sort of stands out - oftentimes, they're meant to be a reveal to a larger world (Either as part of a secret group the protagonists come to seek help from, or more exposition on a situation, or as part of a larger escalation of the conflict of the story.), and the people living on the non-floating ground of Earth aren't usually aware of the floating island, except in legends that they don't know about them until then. At best, the Grounded People believe the existence of the island is a legend, a myth even, even though the Sky People have been around for ages, often millennia.

This however, poses a problem - for this Floating Island is neither at sea on its own (Which still leads to the issue of sailors noticing it when sailing), nor likely at International Space Station levels of height out sight (Or applying the "Move very quickly across the sky" orbital trick to avoiding immediate notice). So, how do they manage to hide themselves from Grounded People when people should just be able to look up at the sky and see it, or potentially notice it through a telescope? Especially on a clear day/night, where cloud cover isn't an option?

Is there a way to hide an floating island from below for any climate situation, and is there an upper limit on when that solution would fail in terms of the technology level of Grounded People?

(I'm presuming it would fail when airplanes and/or spaceship related technologies being up, but I'd like to at least hide the island through the Medieval era tech if possible.).

Bonus if it's a passive way to hide the island itself, and not require active powering of technology to keep it hidden.

Answer 1

The Island is kept aloft by a powerplant that produces steam

Any natural phenomenon that produces cloud cover to hide your island will always encounter weather situations where the clouds dissipate from time to time... that is, unless the clouds are not natural. A nuclear isotope with a long enough of a half life, and in abundant enough of quantity could turn your whole island into a giant natural reactor that could last for thousands of years. However, nuclear power means boiling vast quantiles of water, which means lots of steam, which means the island is perpetually producing its own cloud cover. So, the same power source keeping you in the sky is also keeping you hidden.

Because the reactor boils so much water, the sky people need to occasionally lower a massive pipe down into an ocean, lake, or river to replenish their water supply; otherwise, the system could be mostly passive. Very rarely, someone might notice this pipe, but the sky people don't want the land dwellers to know about them so they are generally careful to only lower it when they are somewhere very remote so the occasional sighting would be by so few people that it would be normally disregarded as a tall tail. But it does happen from time to time. In fact, one time someone even climbed up the pipe, saying he had found a magic bean stalk, but since the bean stalk was gone by the time he could show anyone, no one really believed his story.

Those aren't clouds, it's steam!

~ Migo (Smallfoot)

While not a 100% passive hiding system, this would allow you to stay hidden even after the development of early aircraft since the clouds could envelope the whole island. It would take the discovery of radar to conclusively prove its existence.

For a more passive low tech approach

Make the island look like a cloud. I don't just mean color, I mean shape and texture too. One of the things that make clouds look like clouds is the their shape. They have gaps and funny outcroppings too them. Luckily so do some islands. Many islands, have very cloud like shapes to them; so, if you give your island enough of that shape, then you have half your job done for you. The hard part then becomes, the surface. Just painting the bottom of an island white wont's give it that aerie translucent refractive look of a cloud, but luckily there are some solid materials that have very cloudy appearances. If the entire bottom of your island were encrusted in a thick layer of mostly transparent white crystals, then you could get branches of crystals sticking out the side that create that wispy see-through look you at the edge of clouds, and any side lighting from the sun will shine through it giving it more or less the same reflective/refractive colors of other clouds.

Because the light is so diffused, you do not need exact samplings of adjacent sky to project the way you do with active camo so you can take refracted light from the edges and bend it downward such that no actual light from the top is actually needed to make the structure seem fully saturated with light.

For best results, mix these two methods together

The crystalline bottom will look like just more cloud if it pokes out through the bottom, and the steam clouds will ensure you have an amorphous outer edge so that someone watching your cloud over time does not notice it moving too rigidly.

Answer 2

Psychological warfare. The culture below has been "seeded" and social-engineered into believing that seeing dark objects above is a certain sign of death (Maybe some ancient beasts circled the land once above) and thus, one desperatly ignores the shadow and thing above, praying silently that the evil eye may fall upon somebody else.

Answer 3

What is needed is active camouflage: Either by simply increasing the light emitted by the base of the island with lighting From around 1:13: https://www.youtube.com/watch?v=aIceh3Bk0Cc&t=1s

Or adaptive camouflage where the colour of the background is detected and projected below https://www.youtube.com/watch?v=KL_KdmSTSNA

Close up they don’t work that well but at long range of a mile or two it should work well enough

Answer 4

High altitude lowers water's boiling point

Many depictions of floating islands have some measure of water on them, be it a lake, or some sort of self-sustaining water system via rain and waterfalls and rivers, etc. This suggests the island has some sort of way to create its own clouds, mainly by way of easier evaporation, due to higher altitudes lowering the boiling point of water and making it easier for the sun to turn the water into vapor, and keep itself hidden in its mists/clouds for a little bit even when the rest of the sky is relatively cloudless. High altitude boiling

Depending on the geography of the island it might also 'capture' passing clouds and drag them along with itself for extra cloud cover.

A minor problem comes when someone observes this collection of water vapor for a long enough time that parts of the island peeks through the cloud. This could lead to legends of it cropping up, with those who didn't or can't see what the others saw for that brief moment usually shrugging believing they're a little crazy for most of history.

A bigger problem comes the moment people have recording technology like cameras, or any form of aerial mobility at all with something as simple as a hot air balloon. Then they'll either be able to gather proof or take others with them to confirm the floating island's existence.

The shadows this island will cast down below will also be a problem, and unless during a heavy rainstorm the darkness it'll make will certainly make people curious. I don't know if your island has any special properties(other than floating), but I suggest that wherever it goes there is a rather heavy rainstorm going on either naturally or somehow created by the island.

Answer 5

It is far enough away to look like a celestial body

It can be tricky, thanks to the low altitude compared to the moon or any other celestial body. Yet if the telescopes aren't good enough, it is very well possible a high floating island is regarded as a strange celestial body.

If the island is high enough it can already be difficult to spot. Planes are big, but quickly diminish in size and detail the higher they go. An island can be much bigger and still hide the fact it has life on it.

With strange world views fueled by religion or ignorance (flat Earth), it isn't a stretch that the floating island is just a strangely behaving celestial body. Maybe it's represented in folklore, or a diety, or mabe the island is sort of predictable (doesn't move fast), so it can be an extra navigational point for people taking note where it is in the sky periodically. The fact is, it can be as mysterious and unknown as the moon itself. People will try to explain it, but sky people might be one made up or with a grain of truth story. One in many. That way sky people living on a floating island is as likely a possibility as the rest.

Or unlikely... who would you believe? A person who says it's an object like the moon. You can see some detail, but never enough. Or do you believe your religious leader, telling it's your deity, a great power of unknown that rules the lower skies. Or some scientist with a telescope telling everyone there's people living on a floating rock up there. The premise is so ridiculous that the others seem more likely.

Answer 6

It looks like a bird.

source

Up close it would look like a really really big bird. But it is not up close. It is higher than the clouds and there is nothing next to it to estimate scale. Viewers assume it is a bird flying high up. Really it is a colossal fake bird flying very high up.

Answer 7

Hide it in plain sight. It's a huge rock in the sky, so what. Its been in the sky for a millennia as far as people know. Sure you might find rumors' of the sky people or just as easily the legend of the dragon's living on dragon island. You would have ancient history of countless myths and legends of the great rock spanning for a millennia and none of them confirmed, no changes ever seen for all that time.

Everyone knows it could never be reached as it's more than a 5kM high, no tower can even be conceived that high by man in modern times.

Answer 8

It could be visible but in a place that’s uninhabited, like above the ocean or floating in/above a valley in some kind of himalayan-style mountain range. Somewhat similar to Shangrila.

Those few people who discover it might (a) stay, because it’s convenient or too remote to get back, (b) die on the harsh way back, or (c) return home just spread the same old legend of a place that nobody else believes to exist

Answer 9

Perhaps like Death in Pratchetts' books. People don't see it because there is no such thing as a floating island. Maybe children will see it and tell their parents, they will always be scolded and the adults will turn back to their works on the field...

Answer 10

Counterillumination and an island bottom painted white, with long cloth streamers, will make the island resemble a cloud. When possible, of course, hide among other clouds. Depending on altitude (but how would they breath?), some sort of cloud seeding might be possible to get clouds where ordinarily there wouldn't be.

This is, coincidentally, the method adopted by the mythic Tempestari pirates in the ninth century - they also had machines that ground water, dust and grain and produced a thick fog. They were said to live in the fabled land of Magonia (which possibly comes from magia, or 'Magic'). Their ships were believed to be the cause of hail and thunder, or so the Bishop Agobardus of Lugdunum reports in his Liber contra insulsam vulgi opinionem de grandine et tonitruis ("Book against the silly urban legend on hail and thunders").

Answer 11

If it hangs out off the coast of a continent, hovering about 2km high, ~25km off the coast. Combine this with various other methods others have mentioned, such as produce steam and have a crystal bottom, it would be too distant for people to say "that aint no cloud!" Unless some sailors spend excessive time out to sea under it.

With it being ~25km away from the closest observer and with a crystal structure, at sunrise or sunset (depending which coast your off, it could shine in the sunlight to look like a celestial object. However, this would wreak havoc to early astronomy and will be quickly discovered upon the invention of the telescope.

Answer 12

Try again, supposing it's impossible to hide

This deserves a second answer attempt. On my first answer, I tried to hide the thing from view. That is not going to work, because the inhabitants of the floating island have no technological means to hide their village/city/country size world from view, when it floats in the atmosphere.. to allow the medieval inhabitants of the floating island to breath, it should be below 7km altitude anyway, and avoid high mountain tops. There is no way this rock would not be visible in clear sky.. or occluding stars at night. It will always blow its cover, for people somewhere on the planet. You would need to project a cosmic hologram on the bottom, to make it transparent. Dream on..

Medieval people

Medieval people depended on agriculture. The inhabitants of the floating island will need all their water for growing crops. Fertilization is questionable, the amount of grounds is limited. Living up there will be a harsh life, inhabitants will need to find ways to survive.

When hiding is/was a priority, they are on a wrong plan. They can't hide. Maybe they'll attempt to hide.. but the can't assert if it actually works. From the planet's surface, their island will be visible as a dark blob in the sky, sometimes occluded by clouds.

It can be visible, yet remain unnoticed

Suppose visibility (alone) is no issue. People on the planet are medieval too, they won't know there are people up there. On top of the platform, people are living.. but on the planet, technology does not allow a flyover to prove that. So the people on the planet are unaware of the inhabitants living above, on the floating island. For them, the floating island is a rock in the sky. Like the moon, but not round. For centuries, the platform could be regarded as "just another celestial body in the sky" but much lower altitude, floating in the atmosphere rather than being "another hole punched in the celestial sphere", like medieval people believed. They could assign an astrological meaning to it, but they would actually know nothing. The island is safe.

Science, when it develops on the planet, will want to find an explanation

Drawing a parallel with earth scientific development, you could say in late-medieval times, the presence of this floating rock would turn into a scientific question: what is this rock in the sky ? how can it float ? why is it the only one we see ? how high up is it really ? Questions would arise.. but we're talking Galileo Galilei and Keppler. In all centuries before them, it would not matter what this rock in the sky meant. It was a celestial body floating low, just like a planet, or a small moon. People would get used to seeing it, until they don't notice it anymore.

Answer 13

Go somewhere without too many humans

A floating rock over a dense rainforest makes it too much of a pain to investigate, but still gives you regular rain. For best results, sit on plateau above a jungle, to be as inconvenient as possible to reach.

Answer 14

So, are we really going that way, huh?

You could be statisfied with "it was always there" or "make steam under it so ppl will think it's a cloud" ( =? ), but we know you aren't.

This is not an island of farmers or murlocks, there is an evil archwizzard up there and he WILL have the island cloaked eventually.

So what'd he do? Depending on whether there is magic in the world or not, he would create an optical illusion below the island to cloak it from viewers below. How? Well, not by mounting a big rack of mirrors below it. You'd want to have a flat, convex lense below the island that will break the light in a way that the sky besides the island is visible. How do you achieve this?

You can place a flat body of water under the island , either by magic or with glass, the science way. you then need to make a convex lens on top of that, so it wouldn't be too bad if these where one and the same body. The light needs to be broken in a way that directs the light from the side of the island to the bottom, so to speak. This all serves like a gigantic alchemist's bauble and you basically already know this from physics class ^^

This way you can be a sneaky boii (don't edit this)

Answer 15

Make your own cloud.

Heaps of cotton wool - or something like it. Create a faux-cloud and stick it to the bottom of the island. If it's high enough up then it should be relatively hard to detect until at least the invention of telescopes, and probably longer if it sticks to existing cloud cover where possible.

Answer 16

Put it over the dark part of the moon

On first sight, painting the bottom black will do.. however.. in daylight, your platform would cast a shadow on earth's surface, anyone would see the platform.

At night, your floating platform will hide stars behind it. These stars will move 6 degrees per hour, in respect to an observer on Earth surface. You'd need a running animation on the bottom, inconceivable with medieval technology.

Now suppose the platform would have an near-polar orbit, always accurately placing itself between Earth and the Moon, a few degrees off. The platform's bottom should be painted black, it won't be visible. It needs to be high up, or it would be seen from different angles next to the moon. Also, I haven't solved the 'full moon' situation. So maybe... they would have to paint it over, every month ? With medieval technology, this question is very difficult..

Answer 17

It naturally/magically sails on Clouds.

As in, it cannot free-fly, it instead "floats" in clouds like a boat on water.

Inherently therefore, it cannot be seen because there is always a cloud underneath it to block the view!

In order to ensure that a heavy rainstorm doesn't result in the island crashing to earth catastrophically, the mages of your floating island have cast a spell to call clouds towards the island at all times (or perhaps it's an innate part of the magic that causes the island to levitate in the first place).

Answer 18

Camouflage Paint

The most prestigious job in the Cloud People’s society is being a bottom painter. It’s a constant operation, usually performed under the cover of night, but they keep the bottom of the floating islands painted to conceal them.

They’re oblivious to the fact that the ground dwellers may have discovered the painting operation millennia ago, because the ground dwellers humor the Cloud People.