Stargazing How far can the best telescope see?

  1. Using the best technology available, how far can you see things clearly? As in how many light years?
  2. jcsd
  3. Drakkith

    Staff: Mentor

    We don't use distance as a measure of how well a telescope can see. Instead we use brightness. A super bright object 5 billion light years away can be MUCH easier to see than a very dim object within our own solar system.

    Also, how far a telescope can see has little to do with the telescope itself and more to do with how much exposure time you can get to beat down the signal to noise ratio in the images. Given enough exposure time, my 8 inch telescope could see the same objects that the Hubble Space Telescope can. The difference is that the HST has far more resolution thanks to its larger size along with the advantage of being in space instead of on the ground where seeing ability is limited by light pollution and blurring due to the atmosphere.
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  4. Drakkith

    Staff: Mentor

    Here's a perfect example of what I was saying.

    The Andromeda Galaxy is a little over 2 million light years away and is visible to the naked eye from practically the entire world.

    Pluto is within our own solar system and cannot be seen by the naked eye. (The eye performs the same function as a telescope, so I'm using it as a comparison)
  5. Chronos

    Chronos 10,348
    Science Advisor
    Gold Member

    We can see the CMB, how far is that?
  6. Chronos

    Chronos 10,348
    Science Advisor
    Gold Member

    On the other hand, we have difficulty resolving ordinary stars in the Magellanic clouds.
  7. When you say "how far", I immediately think of the Hubble Deep Field and the Ultra-deep field. Are you aware of these two images?
  8. Isn't "how far" a little bit misleading? I could possibly say that my vision with bare eye is infinite, however what I can actually observe and identify - that is something completely different.
  9. Drakkith

    Staff: Mentor

    Yes, just as we explained above, asking "how far" a telescope can see is meaningless.
  10. My bad, I didn't know that. I got curious when I saw an image in which there appeared to be many stars. But the explanation said many of them were actually galaxies.

    Given enough clarity and exposure, is it possible to observe the happenings in, say, Andromeda?
  11. No I haven't. I'll check them out.
  12. russ_watters

    Staff: Mentor

    Depends on what "the happenings" are.
  13. Like volcanos on the surface of a planet. Just a crude example. Something like that.
  14. russ_watters

    Staff: Mentor

    No, the resolution of our telescopes is a function of their size, due to the physics of how optics work. They have nowhere close to enough resolution to resolve planets, much less surface features in Andromeda.
  15. About 5.8 billion light years. That corresponds to a red shift of about 1.64. We can see light from objects which has been travelling for longer but those objects were closer when the light was emitted.
  16. davenn

    davenn 4,354
    Science Advisor
    Gold Member
    2014 Award

    probably a bit hopeful there ;)
    I would suggest its substantially less than that
    yes we can see objects at several billion lightyears. but resolving ones out to a few 100 million ly's

    note what the OP said .... "how far can you see things clearly? "
    Russ's response gives a better idea of resolution problems

  17. mfb

    Staff: Mentor

    The resolution of our best telescopes is good enough to:

    - see some features of Pluto (of the size of ~500km), but nothing in detail
    - see a few of the biggest and closest stars as a disk
    - see some planets (as spots without any features) around stars nearby
    - track individual stars in the whole galaxy
    - observe some individual bright stars in the Andromeda galaxy

    To see features on planets around other stars, you would need a telescope with a diameter of (at least) hundreds of kilometers.
  18. "clearly" is a qualitative term. The original question suggests that better telescopes can see farther but that is not always the case. We have telescopes that can image objects at z=1.6 and while better telescopes may improve the resolution at all ranges, they can't allow us to see farther.

    Essentially, the only sensible measure of resolving power is angular and range becomes academic.
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