I was wondering what is the farthest the best optical telescope can see into outer space from Earth. What causes them to see so far?

  • $\begingroup$ What kind of telescope? Optical? Radio? X-ray? Please edit your question to give more detail. For further guidance, see How to Ask, and take our Tour. :-) $\endgroup$ Mar 27, 2022 at 1:34
  • $\begingroup$ Optical. My apologies for not being specific. :) $\endgroup$
    – Mintvbz
    Mar 27, 2022 at 4:17
  • $\begingroup$ As I noted in my earlier comment, you need to edit your question to include this information. Clarifying your intention in a comment is insufficient, since comments are (by SE design) impermanent. Not including the information in the body of your question can lead to people adding further answers on non-optical telescopes. For example, the most powerful telescope to date is the James Webb Space Telescope, and it can view objects too distant and faint for the Hubble telescope to pick up, but it primarily operates in mid-infrared rather than optical. $\endgroup$ Mar 28, 2022 at 5:38
  • $\begingroup$ I consider it a bit rediculous to expect the OP to specify the type of scope. Perhaps they don't care. $\endgroup$ Mar 29, 2022 at 16:29
  • $\begingroup$ @GregMiller I really didn't care, I had just been curious. Any would have worked. $\endgroup$
    – Mintvbz
    Mar 29, 2022 at 17:15

1 Answer 1


"How far" is kind of an odd way to measure how good a telescope is.

The visibility of a distant object depends on how bright it is, not only how far it is.

How far can you see with the naked eye? About 10.5 billion light-years. There was a "gamma-ray burst" that was at this distance and would have been visible without a telescope (though there is no evidence that anybody actually saw it)

There are galaxies that are 32 billion light years distant. Further than this is the "surface of last scattering" which we see as a uniform glow of light reaching us as a relic from the big bang. This is about 42 billion light years away, but you don't need a particularly "good" telescope to detect it, you only need a radio telescope. However the surface of last scattering was so bright that it doesn't need a very big radio telescope. You can't see any further than this, since this is almost back to the start of the big bang.

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    $\begingroup$ Wavelength also comes into play due to the expansion of the universe. A very bright object will become invisible as its light's wavelength is stretched. The JWST operates in the infrared because the objects it intends to study are much further away. $\endgroup$ Mar 25, 2022 at 19:33

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