Put the other way around. From how far does visible light reach the Earth to be observable by a telescope that operates in this spectrum?

Gas clouds for instance absorb light. A star behind such a cloud would be not observable, because its visible light does not reach us.


As a matter of fact, the space is almost empty; usually the problem with observing a far star are not the gas clouds between us and that star, but any possible brighter source of light in the surrounding space of that star (e.g. other stars or nebulae). As an example consider, the Hubble Space Telescope, which works in the visible-light spectrum, as well as in the near-infrared and near-ultravioelet spectrum. On the web there are lots of images of very far galaxies photographed using visible-light. Then, I can imagine that with visible light you can see far enough, with adequate instruments.

Also, take a look at this image, taken from Wikipedia, of how far can some present-days telescopes see through the space!

Let me guess, is it possible that your question is motivated by the sci-fi novel Nemesis, by Isaac Asimov? ;)

enter image description here

  • $\begingroup$ I believe the Hubble (Ultra) Deep Field images were taken at infra-red wavelengths, though. I guess the red shift gives a limit to how far you can see in visible light, but I don't know what that limit is. $\endgroup$ – Nathaniel Sep 12 '13 at 15:09
  • $\begingroup$ Hi Nathaniel! Well, according to wikipedia the Hubble Ultra Deep Field images of the 2003 and 2004 are taken in the range of visible light (between 435 and 850 nm), and I believe they are the deeper visible-light images of our Universe ever taken; while those of the 2009 are in the near-infra red, at about 1k nm. $\endgroup$ – AstoundingJB Sep 12 '13 at 19:36
  • $\begingroup$ When you say that "you guess the red shift gives a limit to how far you can see in visible light", are you thinking about "the Infamous Olbers' Paradox"? Actually, the red shift explanation, related to this paradox, explain why the cosmic microwave background radiation has a temperature of about 2.73 K now. Nevertheless, it doesn't explain (or contribute significantly) to why the night sky is black... $\endgroup$ – AstoundingJB Sep 12 '13 at 19:54
  • $\begingroup$ ...for example, UV light at 100 nm emitted by a $z=7$ very far star (more likely, a galaxy!), reaches us as visible red light at $\lambda=(7+1)\times 100$ nm $= 800$ nm. So, what was UV becomes visible and what was visible becomes infrared and hence there isn't a consistent loss of luminosity in the visible spectrum within small red shift of $z<10$. $\endgroup$ – AstoundingJB Sep 12 '13 at 20:03

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