Why isn't the night sky completely lit up with all-white light?

The Hubble Ultra Deep Field image has shown us that in every single square centimeter of sky held at arms length contains on average the light of about 10,000 galaxies, and of course our own galaxy is filled with about 500,000,000 stars - so, why is it that we only see the light of the nearest stars in the night sky, when all the rest of the light from the other stars, and galaxies, has been traversing every point of space across every conceivable timeframe since creation..?

Why can we only see those stars that are closest, and not get the light of every other star who's light the telescopes reveal is present, in which case the whole night sky would be all white light with every bit of it filled with starlight?

Thanks for your imput, no silly answers please because as far as i know this is a very good question.

reply to post by NewAgeMan


My "imput" is that we've destroyed the ability to view the stars with light pollution. We've so many bright cities, we cannot see the dim lights of the stars. Go to a secluded area, you get so see them. From your back door, well no.

Input, I wish it were visible.. It's something we don't really appreciate. The loss of our vision like this.

reply to post by NewAgeMan


imagine.gsfc.nasa.gov...
cosmology.berkeley.edu...

Because visible light output drops by a factor of 4 for every doubling of distance. And we are a LOOONG way away from any of those stars.

And the atmosphere blocks a bit of light too.

We do get the light which is why they are visible through telescope it's just that they are so far away it's like standing in the moon and shining a torch at the earth

Originally posted by fourthmeal
reply to post by NewAgeMan

 

imagine.gsfc.nasa.gov...
cosmology.berkeley.edu...

Because visible light output drops by a factor of 4 for every doubling of distance. And we are a LOOONG way away from any of those stars.

And the atmosphere blocks a bit of light too.

We used to be able to see the stars. We still can.

Just not here - in city land.

lmao, you get the stars tho! I can see yours. Op must want a specific tale, not the truth. haha

Because our atmosphere, and light pollution. And even in space you don't see light from every star so easily, because they simply are too far, and they are very small, points without diameter.

Even in very far from major cities, there is still some light pollution, as sky can reflect light back. Sadly, no one is doing anything to light pollution. Most of world's population has never seen Orion's Nebula with naked eyes, I'm lucky I can see it during very clear weather. Also, I can see Milky Way, which is impossible to see from larger cities.

My guess is because the galaxies and stars are so far away and so tiny that we can't perceive the light from them. It's like trying to read really tiny text on a TV from across the room.

ETA: It could also be the same concept as looking up to the sky in a big city and not seeing any stars. The further you get away from the city the more stars you start to see.

Maybe the stars within our galaxy saturate the other light out like with the city? Good question. S&F

It's the same reason why your headlights at night only aluminate 30 or so meters in front of your automobile, but someone can view your headlights as pinpoints of light from kilometers away. I believe there is a physics term for this.

Olber's paradox

A technical explanation.

The inverse square law, as stated above, is also a good explanation.

Originally posted by elfie
Olber's paradox

A technical explanation.

The inverse square law, as stated above, is also a good explanation.

Thanks for this, at least someone understood the nature of the question posted in the OP.

Even still, you would think more starlight than that eminating from the closest stars would also be visible.. but instead all we have between the closest stars is the blackness of space.

Interestingly, if the starlight of more distant stars WAS visible, the whole nightsky would be a dazzling white, every bit of it.

Originally posted by fourthmeal
reply to post by NewAgeMan

 

imagine.gsfc.nasa.gov...
cosmology.berkeley.edu...

Because visible light output drops by a factor of 4 for every doubling of distance. And we are a LOOONG way away from any of those stars.

And the atmosphere blocks a bit of light too.

The rest of the light from more distant stars should still arrive, eventually, however dimmed down, but we don't see any of it, only the local stars, so even with the inverse square principal, I still don't see how all that starlight is completely blacked out, it's still a mystery, imho.

I think I get it though - the light is there, as can be seen via telescopes, but it's just so dim that everything but the local stars appears black to the naked eye, but it it's still filled with starlight nevertheless as depicted in the Hubble ultra deep field which picked an apparently blank piece of space to look at, which when the photo came in was filled with 10,000 galaxies.

Intersting to note however that the whole sky is filled, every point of it, with almost limitless stars and galaxies.

There are multiple things going on,

First light is not a constant stream, it comes in packets or photons. The inverse square law applies for an isotropic emitter, which a star approximately is to a very very good percentile. So if you double your distance, the number of photos you see per square meter reduces by a factor of 4.

Now the reason hubble can see this faint light is because, it takes very long exposures of the same place in the sky. Our eyes integrate for about - 60 Hz (i think, it could be faster than that depending on what part of the eye) it also has a very small aperture, so when we look up at the night sky we are limited by the exposure limit and the small collection area, the human eye is a logarithmic counter too, and we need about 10,000 or so photos to trigger the cells in the eye to tell the brain that it saw some light.

Space is also not complete vacuum, there is typically 2-4 atoms per meter cube out in space, this increases by about a factor of 10-100 in what could be considered a cloud. These atoms do absorb photons, and further more, any larger pieces of debris such as planetary fragments, stellar remnants and bits of dust the size of a grain of sand would also contribute to blocking out alot of light as it travels from the edge of the known universe to us... a distance of about 13.7 billion lightyears

reply to post by ErosA433


Yes, but what of the cumulative factor, recognizing that by the time the light gets here, it's source might not even still exist - ie: that even the most distant, and oldest light emitting sources have put forth photons which just keep on going and going - wouldn't there be a cumulative factor which would add all the light travelling from all sources at varying times and distances, such that we would get to see more than just the light from local stars?

have you ever looked at the night sky in the woods?? with no city light pollution.

it is heart stopping AWE you can clearly see the milky way with naked eye...the sky is FILLED with stars in every square inch of the sky...its breath-taking!

The first time I seen the night sky like that....I stayed up all night staring at it's beauty!

when I got back to the small city I live in (with barely any lights) I could barely see a handful of stars.

I recommend you take a trip out to the woods or country rural area at night.

You have to go to a dark place and look up to the sky.
I drove into a night spot gravel filled parking lot one end of summer perhaps but
can't remember the exact time.
There was light on a garage shining very brightly but not much else around.
I suddenly thought to look up to the sky.
The sky was filled with the stars of the milky way.
It was incredible.

The stars are so far away they are only pin points of light.
Even in a telescope stars are like pin points of light, nebula are light blurs.

Light waves appear to be coming at you and do nothing else because they are
a result of energy floating in a medium as a wave and can only excite the
appropriate receptors.

I can only refer you to the writings of Tesla and ask those who secret his work
why Tesla said he would light up the night skies for ships at sea to avoid night
time collisions. Tesla's collision avoidance system.

New light has appeared in this matter by Mr. Lyne and his 1000x over unity
Atomic Hydrogen reactions. Not known to Tesla at the time as Tesla only
vibrated gases in a tube to light up but the night sky vibrations might have met
with overunity of gases causing Tunguska or an atmospheric catastrophe.

reply to post by NewAgeMan


Unfortunately there is only the cumulative factor of exposing a 5mm aperture for about 0.2 seconds and require about a million photons to activate the rod cells to constitute your brain seeing something. Even with all those galaxies and all that distance, we simply do not collect enough light. And noise in the atmosphere from city lights and dust scattering means we can only see bright objects... typically those that are nearby.

The Hubble deep field is also made up of many many exposures where the typical total exposure time at each wavelength is about 42 hours... (i am not sure about how many wavelengths they look at, but counting photons for 42 hours on a CCD that only requires a few 10s of photons to register a hit, is far better than the human eye)

about light being blocked... imagine what the far side of the moon would look like during a full moon as observed from the earth... if you where placed behind it, it would appear to block out some of the light you see.

This is in fact what is used to detect some extrasolar planets, the transit of a planet across a solar disc reduces the visible light output of that star... now 13 billion light years is rather a large distance, alot of light never makes it to us though obviously not all paths are blocked.

Same reason you can't see an atom without a microscope.

Also our looking through our atmosphere (especially near cities with high amount of light pollution) is the equivalent of someone with really bad eye sight.

Originally posted by _Phoenix_
Same reason you can't see an atom without a microscope.

Nope you don't get it.

See this Olber's paradox

Every point in the sky contains stars, many of them, at every distance imaginable whereby the light from them has been emiting for eons and eons, some of which may not have got here yet, but much of which has & is passing us by. The Hubble Ultra Deep Field in fact shows that every square centimeter held at arms length (try it) contains the light from about 10,000 galaxies, never mind the starlight from the cloud of our own Milky Way (which is visible absent light polution).

In theory the whole sky could be so filled with starlight that it would be all-white or "bejeweled" (I like that word).

What I've learned however, is that while the light is there, once you reach a certain distance, by the inverse square law, it's so dim that it cannot be detected by the naked eye, and thus appears black.

However, if you took the Hubble Space Telescope and created a wrap around image enveloping the earth at every point of the sky, and at variying magnifications, what would be seen would not be a black sky dotted with stars, and a hazy river-like Milky Way in one section, or even a nebula here and a galaxy there, with black space in between - but a dome of nothing BUT stars and galaxies without any black in between whatsoever!



Thus, even though we cannot see it with our eyes, seeing "only" the local stars in a very very small sphere of space within the Milky Way Galaxy, what's mind-numbingly AWESOME is that in truth, the whole sky IS "bejeweled" every single point of it, all around the whole earth - think of that next time you look at the sky either during the day (imagining what's behind the blue) or during the night (what's in between the stars that are visible).

Originally posted by elfie
Olber's paradox

A technical explanation.

The inverse square law, as stated above, is also a good explanation.

Actually Olber's paradox assumes an infinite number of stars.

A simpler solution to Olber's paradox is that the number of stars is huge, but finite.

I have never seen this as much of a paradox with a finite number of stars. Some galaxies are so distant that one photon arrives at your eye every few seconds. The light is hitting your eye but that's not intense enough for your eye to detect it.

Simple.