Expert: Tom Whiting - 9/10/2008

Question
QUESTION: What is the furthest object known,that could be seen with a telescope?

ANSWER: Hi Jackie,
Depends on what kind of telescope you are thinking of, and what you mean by "seen"....photographed or naked eye?  And using a visible light telescope, or a radio telescope?

Photographed in visible light is the Hubble Ultra Deep Sky photograph
which imaged galaxies that existed only about 800,000 years after
the Big Bang, so their distance is 13.7 billion - 0.8 or about
12.9 billion lightyears distant.  See
http://en.wikipedia.org/wiki/Hubble_Ultra_Deep_Field

If you mean 'eyeball' to the eyepiece, I believe Einstein's Cross
is one of the most distant quasars, gravitationally lensed around
a foreground galaxy. That quasar is believed to be about 8 billion
lightyears distant. (Google 'Einstein's Cross')
[The eye is not as sensitive as a computerized camera called a
CCD, or Charged Coupled Device used on the really big scopes and the Hubble Space Telescope.]

But the real record holder is microwave radio telescopes that can image the remnant light of the Big Bang itself, red-shifted down into the microwave portion of the radio spectrum, only about 400,000 years after the Big Bang, so it's distance is 13.7 - 0.4 = 13.3 billion lightyears. Just Google "timeline of the Big Bang"....
(Of course, it's not an "object"...it's simply photons of red-shifted light, so I guess one of the other answers above would be the
correct one.

So see, it depends on what you call "seen" and what kind of telescope
you are thinking of.  Of course we just launched into orbit a
gamma ray telescope, so maybe soon, it will be the record holder.
Time will tell. Science is always advancing.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA

FOLLOW UP:
Opps, I make an arithmetic error above...the microwave Cosmic Background radiation is 13.7 billion minus 400,000 so it would
be 13.696 billion lightyears distant, and the Hubble Deep Sky field
would be 13.7 billion - 800,000 or 13.692 billion lightyears distant.

And, Just googling 'most distant object seen', I come up with a
gravitationally lensed cluster of stars in galaxy cluster Abell
2218 (not the galaxy cluster itself, but the light that it's lensing)
See, and punch on the picture for the 'red streaks of light'....at
http://news.bbc.co.uk/2/hi/science/nature/3490657.stm
estimated at around 13 billion light years.
The most distant object is always changing every few years as our
equipment becomes better and better...it will always be like that
in science.
Clear skies,
Tom Whiting
Erie, PA


 FOLLOW UP:
Oh, my initial arithmetic WAS correct on the Hubble deep sky photo, at 800 million years after Big Bang, so those galaxies ARE at 12.9 billion lightyears after all. So they are slightly exceeded by the object in the Abell 2218 galaxy cluster after all.

And to learn about our newest Gamma Ray Telescope in orbit, see
http://en.wikipedia.org/wiki/Gamma-ray_Large_Area_Space_Telescope which was just launched on June 11th and is still conducting an all sky survey.
Clear Skies,
Tom  


---------- FOLLOW-UP ----------

QUESTION: in follow up to last question thankyou so much,you did say depends on the telescope used?,it would be the most powerful.

Answer
Hi Again Jackie,Well, to an astronomer, "power" is a relative term. It usually means magnification, but believe it or not, most of us astronomers use our LOWEST power eyepiece 90% of the time.Why?  Because going up in power means you go 'down' in 3 other items;1. There is less light so the image is dimmer.2. There is less field of view, so you are looking at a much smaller piece of sky.3. There is a small loss of resolution, so the image isn't as sharp when you go up to very high magnifications.(Identical to what happens using a microscope for viewing, ahigher magnification causes the exact same thing to happen;just laws of optics, that's all- nothing you can do about itexcept get a still bigger microscope or telescope). Most of the time, especially us who enjoy viewing DSO's (Deep Sky Objects, not planets or stars); things like the Andromeda Galaxy, Ring Nebula, Whirlpool Galaxy, Lagoon Nebula,Globular star clusters, Open star clusters, etc etc. We prefer most of the time to maximize those other 3 items at thesacrifice of only one item, namely magnification. So most of thetime, we use either low, or medium power eyepieces.Realize, we change magnification just by changing eyepieces. Like a microscope, it's the eyepiece that does the magnifying, not the mirror or lens up front. They are just gathering in the light. It's mainly the eyepiece used, that does the magnification, justlike a microscope. But generally speaking, the larger the mirror, the "more powerful"the telescope because it's collecting much more light. And that's whywe want bigger and bigger mirrors, for more light brought to the focus. And it's the same with radio telescopes; the bigger the collection surface of the dish, the more radio radiation can be captured and brought to a single point focus.Hope this answers your question,Clear Skies,Tom WhitingErie PA