How dark is intergalactic space?

[JoeSchmuckatelli]

I still think the people saying you can't see anything are incorrect. 

Dark sky viewing places on earth (if you traveled around to the appropriate N and S Hemisphere locations) allow folks to see 51 different galaxies.  Not necessarily with great detail - but you can see them.  

Given that, I'm saying that the human eye could resolve the visible light in interstellar space, generally. 

Maybe - just maybe - there is a void like the Great Repeller where you can't see much - but I doubt it. 

[kerbiloid]

4 hours ago, cubinator said:

Could the galaxies be packed visually close enough that the clusters would be at least a little visible?

Yes.

All you need is speed.

Spoiler

 

Btw, an idea of UFRT, the ultra-fast relativistic telescope.

Just launch it in arbitrary durection, and watch the whole universe on a signle photo.

Interesting, is it possible to use fine mechanics to point at different gravitational lenses...

[sevenperforce]

On 5/14/2023 at 10:55 PM, JoeSchmuckatelli said:

I still think the people saying you can't see anything are incorrect. 

Dark sky viewing places on earth (if you traveled around to the appropriate N and S Hemisphere locations) allow folks to see 51 different galaxies.  Not necessarily with great detail - but you can see them.  

Given that, I'm saying that the human eye could resolve the visible light in interstellar space, generally. 

Maybe - just maybe - there is a void like the Great Repeller where you can't see much - but I doubt it. 

If you are far enough away, light from distant galaxies will still reach you, but their light will be too dim to be visible. There are voids a hundred times wider than the distance between us and Andromeda.

[lajoswinkler]

It depends on how distant the galaxies in question are. If you are sufficiently far away from them, in one of those large voids, you would see nothing real. Only retinal phosphenes. That would be a scary experience - lack of proprioception and visual signal input would make the brain come up with something on its own because brains don't like zero processing.

The visual reality of space is that it is a black void. Exceptions are highly condensed bodies, luminous or illuminated, and rare examples of nebulas which are frankly always very dim and therefore gray (approaching them does not help as they are not point-like light sources).

There are no vivid colors. There are no rainbow nebulas, no spiky stars, no tantalizing vistas. Sun is not yellow, but pure white or, if dimmed sufficiently, gray. Supernovas' detonations take months and even if we were there, we couldn't see their parts moving outwards because speed is limited to c and they are so enormous. Solar prominences don't fall like rain. It's all so slow because it's all so huge. Fastest celestial movements are starlight suddenly peeking from a planet or a satellite moving out of the way.

Yes, there are photons being emitted which would give us sensation of color if their number was plentiful (and that color would almost always be pink-red with some violet, courtesy of ionized omnipresent hydrogen and helium), but they are scarce and our retinas are small so we see nothing or see a monochrome, almost gray hazy blob. Space is almost entirely (I can't emphasise word almost enough) a black, cold void hostile to life in every single way and that reality is frightening and fascinating at the same time.

[JoeSchmuckatelli]

On 5/16/2023 at 4:38 PM, sevenperforce said:

If you are far enough away, light from distant galaxies will still reach you, but their light will be too dim to be visible. There are voids a hundred times wider than the distance between us and Andromeda.

From what I read, the average person can see celestial objects as dim as +6.5.  Trained astronomers / people with really good eyesight in ideal terrestrial conditions (high, dry, clear and dark) have seen galaxies as dim as +7.2.

Centaurus A, M81 and NGC 253 have all been seen naked eye and are between 12 and 13.7 Mly away.  They have AMs of +6.8 to +7.2.

So what is going to matter is the combination of both distance and brightness such that the apparent magnitude is above +7.2 from the location of the observer - as a floor. 

I've read that the 'average' distance between galaxies is about 9.9 Mly.  Average is in quotes because galaxies are not uniformly distributed - clusters, suoerclusters, sheets, filaments, etc. 

The opposite of a cluster is a void.  The largest void I could find a definition of is the Bootes.  It's apparently 300Mly in diameter.  So, yeah, drive out there and you will see a whole Lotta Nuthin with the Mark 1 Eyeball.  Hubble and Webb would see just fine and you probably could use IR goggles... Which isn't the point of this exercise. 

Place the observer in any region of intergalactic space that isn't a void - and because of the way 'averages' work, the organization of cluster, supercluster, sheet, filament, etc means that most likely you will have a relatively higher density than normal... Meaning the observer should have several galaxies inside a sphere less than 10 Mly in diameter. 

So if these galaxies aren't tiny, or obscured by dust etc - they should have an apparent magnitude above 7, and your intrepid explorer should be able to see them without enhancement. 

cc: 

@farmerben