B Would the Giant Arc be visible from a hypothetical exoplanet?

[Maximum7]

TL;DR Summary

Hypothetical question of whether you could see a giant arc from a vantage point in the universe

I recently watched History of the Universe and they talked about the Giant Arc, a large scale structure that spans 3.3 billion light years long, exceeding the hypothetical limit of 1.2 billion. The Arc was discovered last year.

https://en.wikipedia.org/wiki/The_Giant_Arc

They said if the Giant Ark was visible from Earth, that it would occupy the space of 20 full moons. Obviously, it isn't visible to us, but could there be an exoplanet somewhere in the galaxy or universe that you can see this giant arc from?

 

[Bandersnatch]

With a naked eye? No. Same reason you can't see any but the closest galaxies from Earth. As a general rule, you can't see other galaxies that are farther than maybe a dozen million light years. A few dozen for large ones. And this structure - if it is a structure, and not a chance arrangement - is just a bunch of galaxies stretched along much larger distances.

 

[Vanadium 50]

If you can't see it from earth, going to the farthest known exoplanet gets you 0.00001% closer. Do you think this will make a difference?

 

[snorkack]

With a naked eye? No. Same reason you can't see any but the closest galaxies from Earth. As a general rule, you can't see other galaxies that are farther than maybe a dozen million light years. A few dozen for large ones. And this structure - if it is a structure, and not a chance arrangement - is just a bunch of galaxies stretched along much larger distances.

Is the visibility of deep sky objects to naked eye limited by sensitivity of eye, by skyglow, or by the background of Milky Way?
Naked eye can see Beehive without seeing any single star in it. The brightest galaxy in Virgo cluster is quoted as +8,4, so invisible to naked eye. But what is the magnitude of Virgo Cluster combined? Could naked eye integrate the whole cluster into a visible light patch without detecting any single galaxy in it?

 

[Vanadium 50]

C'mon.

0.00001% closer.

 

[snorkack]

C'mon.

0.00001% closer.

Yes. And the distance between day and night is what, under 1/10 000 of AU, which means under 1/1 000 000 000 of a lightyears. Yet we see nearby stars at night, not by day.
If we looked at night sky from a planet a few thousand lightyears out of the Milky Way disc, without the obscuring glare of Milky Way (on the hemisphere opposite the Milky Way) and without the skyglow of Earth atmosphere, would naked eye see distant galaxy clusters like Virgo as hazy patches of light even if the individual galaxies (M49, M87) were too dim to resolve?

 

[Vanadium 50]

distance between day and night is

With all due respect, that's utter nonsense.

 

[snorkack]

If we looked at night sky from a planet a few thousand lightyears out of the Milky Way disc, without the obscuring glare of Milky Way (on the hemisphere opposite the Milky Way) and without the skyglow of Earth atmosphere, would naked eye see distant galaxy clusters like Virgo as hazy patches of light even if the individual galaxies (M49, M87) were too dim to resolve?

Trying to find some numbers:
The total brightness of galaxy clusters is something which is not quoted commonly, let alone consistently. With some searching, I found:
https://ui.adsabs.harvard.edu/abs/1985AJ...90.1759S/abstract

central 6° radius

The total luminosity of all supposed member galaxies in the central 6° core is 2.4 X 10¹² blue solar luminosities.

The Virgo cluster center is around 55 million lightyears from Sun. Back of the envelope, Virgo Cluster would have about the same luminosity as 1 solar luminosity from distance of 35 ly... in the blue. Visible left unspecified.
1 solar luminosity from 35 ly would be about 5,05. Not too dim for naked eye... for a point star.
The brightest single galaxy in Virgo cluster is M49, at 8,4. Which IS too dim for naked eye. All the Virgo Cluster galaxies combined have over 20 times the luminosity of M49. Virgo cluster is described as 1300 or 2000 galaxies total and 160 bright ones, so makes sense to be 22 times as bright as the brightest single galaxy.
And yet - 5,05 spread across 6° radius, that is 12° diametre...
Large Magellanic Cloud is about the size of Virgo Cluster at 11°x9°... but it is magnitude +0,1. 100 times brighter than Virgo Cluster.
Triangulum Galaxy is about magnitude +5,7, which is half the brightness of Virgo Cluster. And some people report seeing Triangulum Galaxy in dark skies.
But yet... Triangulum Galaxy is reported as 1,2°x0,7°. Which means that it has 80 times the average surface brightness of Virgo Cluster.

So Virgo Cluster, at least on average, is a low surface brightness object compared to such naked eye objects as LMC or M33. (And Virgo cluster is an easy, long discovered object. The giant arc would be harder again!)

Now, I asked about eye sensitivity vs. airglow of the ordinary dark nights of Earth.
On ordinary dark nights, the total brightness of airglow is actually quoted as comparable to the total starlight...
If we could look at skies through an atmosphere which is far darker and clearer than the best dark skies on Earth, how much more dim/diffuse deep sky objects would we see by ordinary good naked eye vision? Is the answer more like "a lot more", or more "only slightly more, we would run into inherent sensitivity limits of eye"?

 

[russ_watters]

There is no magic to a darker or clearer sky. On a good, clear night the sky is close to 100% transparent to visible light, with just the little bit of scattering on the blue end - and closer still to 100% dark, minus the stars. Once our eyes are fully dilated/adjusted in such a setting, an additional percent or two darker/clearer isn't going to change anything.

[edit]
To be honest, I hadn't even heard of "airglow", but it is sooooo faint that we can't see it anyway.

[edit2] Actually, scattering is higher than I realized: Up to 23% blue, from 4% red. This will lighten the sky a bit with scattered starlight, while dimming the individual stars.

 

[Drakkith]

Now, I asked about eye sensitivity vs. airglow of the ordinary dark nights of Earth.
On ordinary dark nights, the total brightness of airglow is actually quoted as comparable to the total starlight...
If we could look at skies through an atmosphere which is far darker and clearer than the best dark skies on Earth, how much more dim/diffuse deep sky objects would we see by ordinary good naked eye vision? Is the answer more like "a lot more", or more "only slightly more, we would run into inherent sensitivity limits of eye"?

You'd see almost nothing more than you can currently see. Based on Russ's post just above, let's assume a 12% average absorption across the visible spectrum. That's only about 0.1 magnitude difference. Even the most experienced observers would have difficulty telling two stars apart if they had only 0.1 magnitude difference, let alone extended and diffuse objects like galaxies and nebulae.

 

[snorkack]

You'd see almost nothing more than you can currently see. Based on Russ's post just above, let's assume a 12% average absorption across the visible spectrum. That's only about 0.1 magnitude difference. Even the most experienced observers would have difficulty telling two stars apart if they had only 0.1 magnitude difference, let alone extended and diffuse objects like galaxies and nebulae.

Reminding of the day again.
Clear daytime sky scatters 12% of the incident light and transmits 88%. Clear night sky scatters 12% just the same and transmits 88% just the same.
At high noon, 88% of the light of any star still reaches our eyes. The problem is that the 12% scattered light of Sun is a much bigger amount.
A part of the diffuse light of clear night sky must be Rayleigh scattered light of nearby stars just like the clear day sky is blue of Rayleigh scattered light of Sun. But it is said that a lot of airglow of clear night sky is actually fluorescence of upper atmosphere somehow excited, for example through incident cosmic rays.

 

[Drakkith]

A part of the diffuse light of clear night sky must be Rayleigh scattered light of nearby stars just like the clear day sky is blue of Rayleigh scattered light of Sun. But it is said that a lot of airglow of clear night sky is actually fluorescence of upper atmosphere somehow excited, for example through incident cosmic rays.

Airglow has a very, very small effect which is only observable in very dark skies with cameras and long exposure imaging. Per this NASA page:

Just a tenth as bright as all the stars in the night sky, airglow is far more subdued than auroras, too dim to observe easily except in orbit or on the ground with clear, dark skies and a sensitive camera.

It's really only a problem for when you're trying to image extremely dim objects whose magnitudes are well beyond what most amateur astrophotographers would try for. Light pollution from manmade light sources is much brighter than skyglow except for locations with the darkest of skies (mag 18ish vs mag 22ish for urban vs excellent dark sky site).