Submitted by ArmchairSpinDoctor t3_z0z4ng in askscience
In scifi we always seem to see space as a place where you can see the ship a mile away just fine. If theres no sun or if the sun is really far away how dark would it be? Would it be like being in a cave?
So to travel safely in space I guess the ship would have to emit an insane amount of light in all directions to properly monitor for potential collisions. The odds of one are low I guess, but you'd want to know if an object was heading your way.
Perhaps a sort of infrared sonar would be more useful and energy efficient? I dunno.
Like.. insanely low. So low, that I have no idea where you’re at in the world, but if I got into a car right now, closed my eyes, and drove in a straight line.. I would probably have a better chance of hitting your house.
Space is really empty
If you're picturing dodging like in star wars flying through asteroid fields, that's not what space is like
In our asteroid belt, average distance from an asteroid to the next closest asteroid is about 100,000 miles
For the probes that have gone through the asteroid belt, they had absolutely no way to know if there was an asteroid coming, because the risk of even a single one was basically negligible.
Oh didn't know it was THAT spread out. How packed would saturn's rings be ?
Very packed - so packed that although the rings are just 10-100m thick, they block most light going though them
run fact edit: Saturns rings are some of the thinnest things known to us. They have a diameter of ~1 million kilometers.
The combined mass of everything in the asteroid belt is only about 3% of our moon. And 60% of that is tied up in the four biggest asteroids.
https://en.m.wikipedia.org/wiki/Asteroid_belt
Insaaaaaaaanely sparse.
You're off by a factor of 6 with average asteroid distance - and that's just in the most dense parts of our asteroid belt (about ~1,000,000 km or ~620,000mi).
Radar but space is a lot of empty. The biggest problem is likely micrometorites and high energy atomic scale particles chewing away at you.
SONAR (SOund Navigation And Ranging) wouldn't work since sound relies on having an atmosphere or body of water/molecules to travel. RADAR (RAdio Detection And Ranging) would be much more effective because radio waves can actually travel through space.
Thank you. I was thinking of something that sent out pulses of light to read reflections in the same way sonar does but hadn't thought that radar already does the job just fine!
If you’re flying in space, you’re not relying on the visual spectrum to avoid collisions. Radar will work just fine.
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Just scan ahead of you with a 1meter laser as it boils off a mm of whatever you'll see it.
I mean, you'll see a laser reflected back right? Is there much detail to be observed this way?
Depends on how powerful a laser it is, if it's strong enough to ionize the material a spectrometer will give you an idea of what it's made of, if not the glare will only tell you something is there.
A lot of people probably imagine that if they were just in the right spot, they would see something like the Hubble and Webb deep space images of thousands of galaxies. Nuh uh. Those pictures only exist because the telescope was gathering light for many hours or even days. Our eyes will never see anything much except the pin pricks of light from stars in our own galaxy and faint smudges of the neighboring galaxies.
One is the things that blew my mind is when I found out that the reason Andromeda is so hard to spot in the sky isn’t that it’s small, it’s because it’s so faint. It’s actually much bigger than the moon in the sky!
Just to add...
It is the furthest thing you can see with your naked eye. You have to use averted vision to see it so the rods around your fovea get engaged. They are more sensitive to dim light.
What is this averted vision business you speak of?
The center of your vision is less sensitive to dim light (but much better at seeing color) than the periphery, so averted vision is looking at the blank space next to a dim thing you want to see, so that the sensitive part of your eye sees the dim thing
Ah, thanks! I’ll try it.
This is also why you "see things from the corner of your eye." Your visual clarity is best in your central field of view, but your eyes are actually better at detecting motion at the periphery of your view. Your eyes detect the change in light better at the edges and your brain says "something just moved."
You can try this in your own house. Just find a place with almost no light, let your eyes get accustomed to the dark, and then try to look an objects straight-on. They're very difficult or impossible to see. Then try looking next to that object. You should be able to see it.
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Farthest you can easily see. Experienced observers in exceptional conditions can see some things that are farther away!
Is this actually true, because if so that’s incredible. I had no idea, and to think our nearest planet is a speck smaller than the moon. That’s insane.
It's not even that dim either, it's just drowned out by the light pollution of our own galaxy.
Also, the deep field images aren't in visible light. They're red-shifted into microwave wavelengths, far outside the visual spectrum. The pictures of them require shifting the observed data back into a range we can see.
Incidentally, not being able to seem the with the naked eye is a good thing. If we could see all the stars in the observable universe in visible light, the night sky wouldn't be dark. Thankfully, the expansion of the universe solved that problem and we don't just have to pretend.
I’ve never seen that link before. Thank you for making my night.
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If it’s the Webb telescope making the images, then it’s only in the far infrared.
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Like being in a cave, basically yes. For the human eye anyway.
Presuming you're in deep space in a spacesuit, with no light sources of much consequence, then in principle you wouldnt be able to see your hands in front of your face.
The galactic plane though would be very clear. I don't know if it would produce enough light for you to be able to actually see yourself, but it would definitely provide a background against which the shadow of your limbs would be visible and you'd have a sense of orientation.
If you were in extragalactic space, you would have no galactic plane, but you would have billions of galaxies and stars, which might provide enough light and variance for you to at least perceive shadows of your limbs and some sense of position.
You can see well enough to walk around by starlight on earth. It has been a long time since I was that far out, with only a small town 50 miles away, and no cities for hundreds of miles. but I remember being able to read very large text by moonlight , and to walk by starlight. Can’t remember if I could see my hands or what, but there is definitely far far more light than in a cave
https://en.wikipedia.org/wiki/Orders_of_magnitude_(illuminance)
Here are the numbers. I can verify that you can hike rough terrain and read large lettering by Moonlight. This was especially true in the winter with leaves off the trees and snow on the ground reflecting the light. But I did not find this to be the case for starlight but it was most definitely not pitch black like a cave. So I hesitantly agree with you.
Note that it is possible for retinas to be able to see different levels of dim light. I have no proof of that so I am just guessing. I have an extremely rare retina disease, and it is very difficult for me to see things at night. And now during the daylight as the disease progresses.
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Afaik, the light on a moonless night is mostly red and green light refracted across the atmosphere from the sun on the other side of the planet.
I've seen some charts suggesting starlight could be strong enough in isolation to illuminate, but it's still drowned out by the relatively bright sunen when it's behind the planet.
>hlight. Not a chance. I flicked a lighter's sparker to flash a momentary light. Another one was riding a bicycle in a VERY dark spot in New Zealand wi
Your comment interested me so I did some googling. Looks like light doesn't actually refract all the way around the earth but the air of the atmosphere actually emits light through various physical processes (airglow). Zodiacal light is also a significant contribution.
https://en.wikipedia.org/wiki/Sky_brightness
The above article is about the apparent brightness of the sky itself and puts starlight at ~7% of the total contribution
The link below directly addresses illumination on the ground and puts starlight at about 1/5th of the total contribution. So away from the atmosphere it would be a lot dimmer for sure but still brighter than a cave~
Very interesting, thanks!
I've been out on the ocean at night, and it's the same thing. I couldn't exactly read by starlight, but I could see enough to not trip over things.
Once your eyes are fully adjusted a full moon is surprisingly bright. I've turned off my headlight and hiked by moonlight.
In deep space though the light reflected off an object would suffer from the inverse square rule so this faint light would quickly dissapear into the background.
Rainy night deep into the woods in the Adirondacks and I needed to follow trail markers with no flashlight. Not a chance. I flicked a lighter's sparker to flash a momentary light. Another one was riding a bicycle in a VERY dark spot in New Zealand without a light. I would ride until my wheel hit gravel, feel for the edge with my shoe, then continue to follow the road until I ran into something.
> rainy night
I would think that makes a big difference. Your not going to get a lot of starlight when it's overcast.
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I've been out in the Australian desert on a moonless night. I could easily walk around and see where I was going.
There was a super nova in human history that was bright enough to cast a shadow on a moonless night. I believe it lasted for a few days.
So if one is between stars and was lucky enough to have one go off, would have some level of illumination, but maybe very faint.
Depends on how close the are to that star that went boom. It might be VERY bright.
I always imagined that if earth was by the galactic core then there would be no night like we have now. It would be like twilights at night because stars are much closer together
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In the case of Starfleet starships in “Star Trek,” for example, the ships are self-illuminated (there are lights outside the hull that project light unto the hull), which is why they’re visible in deep space (for TV reasons, of course).
I like the description given by the cinematographers for the lord of the rings when asked where the light was coming from in the night scenes. "The same place as the music" was their answer.
Ooh thats a very interesting take on it, I’ll have to remember that one
Can the characters see the light but not hear the music?
Well in the case of Lord of the Rings, the lighting was at a level that made it so you could reasonably see about what the characters would already be able to see after their eyes adjusted to the dark. So it doesn't really cause any discrepancy, it just makes it so the cameras could see things as well as the people there would and makes the whole thing a lot more watchable.
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Someone much, much smarter than I could explain it in more detail. Deep space isn't so much dark, it's empty. For trillions of miles in every direction and VERY rarely on occasion, there's just absolutely nothing out there.
You'll have the near-speed-of-light particles possibly hitting you full force and that's lights out for any piece of technology we're currently capable of inventing. But to SEE something is to DETECT it, yes? To Perceive it. Human eyeballs are good at doing that -- but not perfect.
We see in the visual spectrum. Scaled up a few orders of magnitude, we have the James Webb Telescope, capable of 'seeing' hilariously further, in ridiculous detail, than the human eyeball. One pixel of it's resolution across ten days could provide an orchestral extravaganza, an avalanche of light and beauty and galactic prowess. It's stunning, really.
But even the JW has it's limits. That's just. how. dang. big. the expanding universe is. It is SO big, in fact, that the further out you go -- past all of the light we can see with our eyes -- the fewer and further between even atoms become. So much so that you'd be lucky to find one at all. And when there's nothing out there, seldom even the light of the stars around you, it's not just dark. It is a dark that we cannot even truly Perceive.
There just isn't enough 'stuff' to interact with other 'stuff' for us to 'See'. Imagine dark to a few orders of magnitude. Scary stuff.
Not the smart guy you ask, but been doing astrophotography. The number of stars one can see even with just a little bit more exposure time is amazing. And that is just about the visible light... well mostly. I would not call deep space dark.
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The darkest places on Earth, on a moonless night, are pretty close to what it would be like in instellar space. Although even then there are light sources not present in interstellar space such as the planets, zodiacal light, and airglow.
Bortle 1 locations on land are rare indeed.
Near a star, on the other hand, the starlit side of a spaceship will be highly visible, while the unlit side will be virtually black. But all spacecraft and decent-sized celestial bodies glow in the infrared.
Just as a little anecdote - I was lucky enough to get to do not one but two observing runs at the IRTF at Mauna Kea as an undergrad, and let me tell you, you haven’t experienced dark until you step outside on the summit of Mauna Kea at midnight.
Like locked in a sealed closet dark. Not being able to see your hand in front of your face while outside is a trip, especially for a jersey boy like myself who isn’t used to any kind of true darkness lol. (Also being able to see Andromeda with the naked eye is mind blowing)
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Technically it would be twice as bright in interstellar space. Since it's lit by a sphere of stars, not a hemisphere. Of course, you can only see one side of an object at a time, so as lit from above in those places. Roughly half the side lighting.
So in space we have an illusion that you will always see stars in the distantance.....it's actually much more terrifying. You might end up not being able to see any light at all , you asked how dark it would be, it would be to dark to see your own hand infromt of your face. No diffrence from closing your eyes.
The shadow contrast on objects even in orbit is severe. The darkness is so deep it makes it impossible to see without artificial light. Astronauts say the change from daylight to night is dramatic and sudden and so is the drop in temperature.
It depends on where you are in the Universe. If for example at a certain point you spontaneously came into existence in the middle of certain cosmic voids. If this happened in a not so distant future. Then the edge of that void would be moving away from you at the speed of light. That would mean that light from those stars couldn't even reach you, and any light from you would never reach the edge of the void. That to me is ultimate blackness. If you want to talk about the darkest part of the Universe those may not exist yet.
An interesting side effect of the expansion of the universe is if the false vacuum collapses in one part at a certain distance that becomes isolated from the larger universe. So no matter how bad things get in one part as long as nothing is faster then light there will always be hope of some sort. May you never be born to the void.
It’s not like you’ll be able to do anything about it if it happens in YOUR part or the universe. :)
True but I still feel solace that nothing besides the heat death can destroy the entire universe. In that sense we will have left a mark of sorts. The collapse into the false vacuum might even be the start of a new universe since it would liberate so much energy. You could get Kugelblitzs forming possibly. It's hard to think what the new rules would be because so much is dependant on that one tiny thing. What I do know is the speed of light wouldn't change that much.
Why don’t you calculate the light intensity? Think of the sun as a point light source like a light bulb. The intensity declines as the inverse square of the distance in all directions I.e. a sphere. The intensity is a rate of photons per square area. The fact the light drops off as a square of the distance the intensity drops off pretty quickly. However when I studied physics in college I learned experiments with the human eye indicated that humans when accustomed to extreme dark are able to see/detect an extremely low intensity of photons. But yes space is dark. Even with the countless numbers of suns the distances between bodies and other light sources makes space a generally dark place. The cosmic background radiation from the Big Bang is just under three degrees Kelvin (energy, which are photons) These are remnants of photons traveling around space left over from the Big Bang. However because there’s matter and light no matter how large the universe expands to there’ll always be some background light or energy. This is the wonderful thing about math. It can help you understand the universe and things like this question.
what if the the universe would be bathed in "light", maybe not seeable by the naked eye. "but felt" as it is really bathed in EM radiation and other more exotic manifestations of energy perturbations in much higher magnitudes.
would it be so truly dark? what if you were seeing fake light. like photons emitted near your eyes/retina from other higher energy "not visible" sources
then there is the fact that every body in the observable universe is exerting a force on everything else no matter how negligible. while that tis not visible light being emitted and travelling to our eyes. its almost like everything of any mass/energy is sort of reaching out and touching you, our retinas and other sensitive parts of humans are tiny and pick up all kinds of interaction. so who knows what deep space is like to human beings? not great.
kind of like the flashes' the first astronauts were quietly reporting they were seeing even sometimes with their eyes closed.
Most things in sci-fi scenarios happen around planets or at least around some star system so it's quite natural that the ships are visible. What cinema shows usually wrong is the contrast. In movies you see most ships in sort of an ambient lightning with soft shadows where you can pick up all the details. We are used that on Earth sunlight reflects from the floor, walls atmosphere and you never see pitch black shadows even in the low sun. In space you will likely see only illuminated areas of the spaceship while the rest will be just nothing, only a shadow against the stary sky.
I feel like most sci-fi misses how dark space is except for The Expanse. Even they had to brighten things up a bit for TV, but that shows realism is one of the things that kept me watching the entire run. They don't shrug off what would be lethal g-forces with magical devices like inertial dampers. Nope, you get strapped into a chair and you have to take it while the skill of the pilot (and some scifi special drug) is what keeps you from having a stroke.
And then you realize the ships aren't long flat decks like in Star Wars. They're actually like flying skyscrapers because the engines impart g-force on you while accelerating towards your destination and then the ship flips end over end and fires it's engine the opposite way to slow down. Equal and opposite reactions there folks.
It's really a cool series.
Deep space just means you're not in orbit. Could be somewhere in the solar system, between solar systems or between galaxies.
If you're still in the solar system, then the sun is shining right at you. If you're in a space suit, doing some maintenance on your ship, you most probably oriented your ship so that you work in the sun. So you can see what you're doing. Your ship will be lit up as bright as day. Assuming you're at a distance equivalent to the Earth.
If you're much further, it will still feel like working at night but with a bright projector lighting up your work area.
If you're much closer, it might be too bright, you might actually orient the ship so you work in the shade. Then you won't be able to see squat without a flashlight. It'll be just as dark as if you were ligthyears away from a start system.
If you're between solar systems, it's as dark as a moonless night. You're still bathed in the light from the stars. Which is usually not enough light to do work outdoors. And whatever solar panels you brought are now just weighing you down. Jetison. If you're quite far from Earth, more towards the center of the galaxy, there'll be way more stars in the sky. But it'll still be too dark to read.
If you're out of the galaxy, then it's pitch black. I mean properly out, right. Of course if you have just left a galaxy, you'll still be able to see it if you turn around. I mean properly halfway between two averagely spaced galactic clusters. Proper intergalactic space.
Without a flashlight, you wont be able to see your hand waving in front of your face. There are galaxies full of stars all around you, but they are all billions of lightyears away, and your eyes aren't good enough to pick them up. I mean, Andromeda is a huge galaxy that is incredibly close to the Milky Way, and it appears at a diffuse cloud. Back in the days we didn't know about galaxies, we used to call it the andromeda "nebula" which is just latin or greek for "cloud". Pitch-ass black. nothing to see.
As a rough estimate, the illumination should be of the same order of magnitude as a clear, moonless night on Earth, which at about 200 microlux of illumination is about 500 million times fainter than a clear summer noon at mid-latitudes, or about 1250 times fainter than a full moon.
With fully dark-adapted eyes, it won't be complete blackness, but it would be pretty damn close, certainly too dark to make out anything but rough shapes. If you want any fine details to be visible the way they are on ships in scifi, you will need artificial illumination.
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I think that space is much darker than a cave. A cave would be a hole in the earth, about 300 K maybe, some more or less. The microwave background is about 3 K. In your question we assume the stars to be far away, so we disregard them. I'm also disregarding thee gases, they'd emit light, too.
Kerfudamapa t1_ix8fggy wrote
I believe It all comes down to the angle of light hitting it and being reflected to your eye, and the amount of light that is being reflected really.
In sci-fi, we'll see a spacecraft in detail because that's what the audience is expecting but, more than likely, in deep space with a vast amount of distance to the nearest star you probably wouldn't be seeing much.
However, the same goes for a moon-sized spaceship that is sitting in the earth's shadow in our own solar system. If there's little/no light hitting it that is reflected to your eye then it's effectively invisible to us.
The point being, while all objects do emit light (usually in the infrared; Google black body radiation) it becomes increasingly difficult to see reflected light from a small source point, onto a small object, that you are well distanced from. Maybe if you plan on venturing into deep space you should bring a floodlight or two?