# Is there a place in the known universe that there would be no visible light from other stars/galaxies?

Is there a place in the universe where, with the naked eye, you wouldn't see any stars, galaxies or light emitting phenomena? From what I understand at some point into the far future in Earth's location, we wouldn't be able to see anything. Is there a place like that could be like that now?

p.s. Not sure what the appropriate tags to put on this question. Feel free to add/change tags as needed.

• The surface of Venus or Titan. Jan 14, 2017 at 21:02
• @DavidHammen Or Krikkit... Jan 16, 2017 at 10:41
• Quite possibly Bok globules: en.wikipedia.org/wiki/Bok_globule Jan 16, 2017 at 16:57

If you don't want to look at the stars and galaxies, you can do two things: You can travel so far that they're too far away to see, or you can block your vision.

## Go far away

On large scales, i.e. above a billion lightyears or so, the Universe is observed to be roughly homogeneous. On smaller scales, however, matter is distributed in the so-called cosmic web, where galaxies lie in filaments and sheet, meeting each other in knots (where the largest clusters are found). In between these overdensities, there are underdensities known as voids. These voids are virtually free of any luminous matter, and since they're up to several million lightyears across, you could place yourself in the middle of such a void and only see darkness.

As an example, consider a void of 100 Mpc (~300 million lightyears) in radius, corresponding to a distance modulus1 of $\mu = 35$. If a Milky Way-like galaxy (absolute magnitude2 $M=-20.5$) were at the border of the void, its apparent magnitude3 would be $m = M+\mu = 14.5$, invisible to the naked eye.

A small telescope, however, would enable you to see galaxies from here. The limiting magnitude4 of the naked eye is roughly 6–7 (though some claim to be able to see $m=8$ objects), so the Milky Way-like galaxy would be roughly 8 magnitudes too faint to see. The gain in limiting magnitude when using a telescope is roughly $g = 5\log(D_\mathrm{tel}/D_\mathrm{pupil})$, so with your 6 mm pupil, a telescope with a diameter of $$D_\mathrm{tel} = D_\mathrm{pupil} 10^{g/5} \\ = 6\,\mathrm{mm}\times10^{8/5} \\ \simeq 200\mathrm{-}250\,\mathrm{mm},$$ would enable you to see Milky Way-like galaxies from the center of the void.

Note though that no matter how far you are from galaxies, there will always be some radiation around, if nothing else then at least the CMB. Of course, being microwaves, this is not visible to the naked eye.

Apart from going down in your basement and turn off the light, could there be "astronomical" places where you would be unable to see anything? As David Hammen comments, at the surface of a cloud-enshrouded planet or moon, you could face total darkness (at least on the night-side of the planet). But perhaps you could also, as Wayfaring Stranger comments, go inside a dense, interstellar cloud.

Bok globules are small ($R\sim10^4\,\mathrm{AU}$), dense ($n\sim10^{4\mathrm{-}6}\,\mathrm{cm}^{-3}$) nebulae of gas and dust. A sightline from the center of such a cloud would result in the apparent magnitude being extincted (i.e. increased) by up to several tens in visual light. The largest extinction through the center of a Bok globule that I've been able to find — but I'm not expert on this — is "FeSt 1-457" with a visual extinction of $A_V = 41$ (Kandori et al. 2005), so from the center and out is roughly $A_V\simeq20$. That means that the fraction of light from outside sources that make it into the center is $$f = 10^{-A_V/2.5} \sim 10^{-8},$$ which is not a lot. However, Bok globules are found in the vicinity of young stars which tend to be bright. An O star has an absolute magnitude of $M\simeq-4$. Such a star located right outside the cloud (say, at a distance of $d=2\times10^4\,\mathrm{AU}=0.1\,\mathrm{pc}$) would have an apparent magnitude of $m=M+\mu+A_V\simeq6$, and thus be just visible to the naked eye, albeit very faint. And if it were just a little farther away, you wouldn't be able to see it.

I assume that you're human, but if you are in fact a cichlid, you should be able to see infrared light (Meuthen et al. 2012). In the IR, the extinction is much smaller than in the visible, so hiding in a Bok globule won't help you.

1The distance modulus $\mu$ is a logarithmic way of expressing distances: $\mu \equiv 5\log(d/10\mathrm{pc})$.

2The absolute magnitude $M$ is a (logarithmic) measure of the luminosity $L$ of an object: $M=-2.5\log(L)+\mathrm{constant}$. Note the minus sign; the brighter an object is, the smaller $M$ is.

3The apparent magnitude $m$ is a logarithmic measure of how bright an object looks to an observer, and so depends on the distance to the object: $m = M + \mu$. Stars visible to the naked have roughly $m=0$–$6$. Again, the smaller the number, the brighter the object is. An extremely distant galaxy may have $m=30$, while the Sun has $m=-27$.

4The limiting magnitude is the largest magnitude (i.e. faintest object) visible.

• I think the statement you're trying to make is... No... but it's hard to tell with all of the extraneous jargon you've used. If that is the case. +1 Jan 15, 2017 at 3:47
• @LaserYeti: My answer is "Yes, there is such a place; you can put the telescope in the middle of a void", but as I try to explain — using extraneous jargon — it depends on what the OP means with "naked eye strength telescope".
– pela
Jan 16, 2017 at 8:31
• I added some footnotes to explain the astronomical terms.
– pela
Jan 16, 2017 at 9:28
• @pela - I was meaning as if someone with normal vision were floating in a hypothetical glass bubble with nothing else to aid their vision (telescope, binoculars, etc). Horrific as that sounds. Jan 16, 2017 at 18:00
• @iMerchant: Okay, in that case you should be fine in the center of a void. Well, perhaps "fine" is not the right word here…
– pela
Jan 17, 2017 at 9:47

Here's a simplified answer. "About" the farthest thing we can see with the naked eye is the Andromeda galaxy at about 2 million light years. Therefore, I would say that you just have to be in a void with no galaxies closer than about 2 or 3 million light years. I could be wrong, but I'm thinking that this is most of the known universe. As far as future Earth goes, it won't be about distance, but about when the last star close enough to see "burns out, which will be a VERY long time from now. There may not even be an Earth then, if it is engulfed by the sun going red giant.

• 2-3 million lightyears is nowhere near the radius of the known Universe, which is 47 billion lightyears in radius.
– pela
Jan 26, 2017 at 11:50
• @pela .. Sorry, I'm afraid my sentence was ambiguous. What I meant is that, I'm not sure but, I think that most locations in the known universe are at least 2-3 million light from the nearest galaxy. Jan 29, 2017 at 19:32
• Okay, I see. You're right that this is roughly a typical distance between galaxies in filaments and sheets, but in voids it is much, much more.
– pela
Jan 29, 2017 at 20:53