Author Topic: "How far can your telescope see?"  (Read 79 times)

Michael Greene

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Re: "How far can your telescope see?"
« Reply #15 on: January 20, 2018, 04:27:34 PM »
Lately I put it this way.

I say: Imagine it's night and there's a mountain ten miles away. A person is standing on the mountain next to the car. Can you see that person? No. So you can't see ten miles. Now that person turns on the car's headlights and they're pointed right at you. Can you see them? Quite likely, even at ten miles. So now we can say you can see ten miles at night.

So, how far you see distant things depends on how bright things are.

Then you can say well you can see Andromeda naked eye, that's 2 million light years; and in the telescope the brighter things are the farther you can see 'em, as the quasars Jon mentioned.

So how dim can you see and how far can you see are two related concepts. There are very close things (cosmically) that our amateur scopes don't see, such as brown dwarfs; and things that our scopes can see, but only photographically.

It's a question in which has the potential to pack in a lot of information in the reply. And somewhere in there you might even mention that the more light you collect the dimmer, and hence further, you can see.

Greg N

Mike Brown

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Re: "How far can your telescope see?"
« Reply #16 on: January 20, 2018, 05:05:11 PM »
I suspect this question is so hard to answer because the asker doesn't understand what they are asking. To truly answer the question, we have to explain what telescopes do. I don't think there's any way around that. You could say, "I can see pulsars 2 billion light years away!" Which is technically an accurate answer, but probably not what they were looking for.How far can my telescope see? That depends on what you want to see.

Picture a ship's captain peering through a spyglass at another ship. With his unaided eyes, he could see the ship just fine. What he wants to see are people on the decks. Why can he see them with a telescope, but not his eyes? Because they are too small. The telescope makes them big enough to see.

Telescopes make things brighter and bigger.

Looking at things in the sky is different than looking at things on the ground. They are vastly further away. We can only see things that are already pretty big and bright. For example, we can see mountains on the moon, but we can't see the Apollo landers. We can see Jupiter's Great Red spot, but that's bigger than the Earth. We can see stars, but they mostly just look brighter. They're too far away for us to see them as more than a point of light, even through a telescope.

With your unaided eyes, you can see Andromeda, another galaxy! With a telescope, you can see more detail...but you can't see individual stars. They're too far away. Some things are so far away we can't see them with our eyes. They're too small and dim. A telescope makes them bright and big enough to see, but only just.

But hey, don't take my word for it! Have a look for yourself...

An explanation on that level might cause their eyes to glaze over. Or, it might spark their interest. If it does, yay! You just made a friend. If not, then they'll hopefully wander off and take their lack of enthusiasm with them.

satimoja

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Re: "How far can your telescope see?"
« Reply #17 on: January 20, 2018, 07:52:59 PM »
My telescope can see galaxies up to 50MLY well, but galaxies get pretty small at 200MLY. However, it can see bright points of light such as quasars up to 12BLY away, or over 80% across the visible universe.

Chad Fithian

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Re: "How far can your telescope see?"
« Reply #18 on: January 21, 2018, 01:14:20 AM »
Quote
However, it can see bright points of light such as quasars up to 12BLY away, or over 80% across the visible universe.

How do you do that with your eye and a 6" SCT?

bunkreplterpka

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Re: "How far can your telescope see?"
« Reply #19 on: January 21, 2018, 08:28:03 AM »
All of the telescopes I own are capable of seeing just as deep as any other land-based telescope, regardless of size. The only reason that huge telescopes are able to produce images as nice as they do is because waves of photons that emanate from some object managed to fall on their mirrors or lenses. It only stands to reason that if these photons are falling on huge mirrors/lenses, they're falling on my relatively diminutive scopes as well. The difference is that in the large scopes, an image is formed that exceeds the luminance of the background noise, whereas in smaller scopes, the image may not actually exceed this level and an image is not perceived, although it is there. So, I would have to say that my scopes are able to see to at least the end of the known universe. I suppose this is an over-simplification, since the diameter of the mirror or lens does limit the resolution due to diffraction properties. Still, the question is "How far can your telescope see?", not "How far can your telescope see well?".

Bill

dextcinthrervest

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Re: "How far can your telescope see?"
« Reply #20 on: January 22, 2018, 11:19:21 PM »
Quote
All of the telescopes I own are capable of seeing just as deep as any other land-based telescope, regardless of size. The only reason that huge telescopes are able to produce images as nice as they do is because waves of photons that emanate from some object managed to fall on their mirrors or lenses. It only stands to reason that if these photons are falling on huge mirrors/lenses, they're falling on my relatively diminutive scopes as well. The difference is that in the large scopes, an image is formed that exceeds the luminance of the background noise, whereas in smaller scopes, the image may not actually exceed this level and an image is not perceived, although it is there. So, I would have to say that my scopes are able to see to at least the end of the known universe. I suppose this is an over-simplification, since the diameter of the mirror or lens does limit the resolution due to diffraction properties. Still, the question is "How far can your telescope see?", not "How far can your telescope see well?".

Bill


Heh, good luck making that argument.

I once tried this when someone asked me what the farthest planet I'd seen was. I said, "Most stars have planets, and light reflected off them reaches us. So every time I look at a star, I see planets that arereallyfar away."

His response was an exasperated, "No, but what's the furthest planet you'veseen?"

...Saturn.

pafunsirep

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Re: "How far can your telescope see?"
« Reply #21 on: January 23, 2018, 10:47:45 AM »
"Between 1 Billion Light-Years to 12 Billion Light-Years depending..."

An excellent, accurate, and concise answer.

I had a very moving experience a few years ago by imaging the quasar APM 03279+5255, at 12 billion light years the farthest object in the readily visible universe and visually within reach of large amateur telescopes, and easy reach of a modern DSLR. Seeing this object in real time with my camera is an experience that I will never forget and is #1 on my bucket list to see visually.

APM 08279+5255 – Quasar in Lynx
Telescope: Meade SN8, Orion Atlas EQ-G
Camera: Gary Honis Baader Modified Canon Rebel T2i
Filter: Orion Imaging Sky Glow Filter
Guide scope: DSX-90, DSI III, PHD
Exposure: 28x60sec, ISO 1600 saved as RAW
Darks: Internal
Flat: Synthetic
Software: Backyard EOS, Deep Sky Stacker, Nebulosity, Photoshop
Very neat stuff.


erafquacor

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Re: "How far can your telescope see?"
« Reply #22 on: January 25, 2018, 12:55:15 PM »
thistelescope see's back in time muchmore then far away. that should get you some attention!

reaipasjime

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Re: "How far can your telescope see?"
« Reply #23 on: January 25, 2018, 06:29:06 PM »
Thanks everyone for such insightful responses.

I believe the question comes out of a misunderstanding of what an astronomical telescope does and, ultimately, the nature of light and distance. They think the purpose of a telescope is to enable one to "see faraway objects." This may come from personal experience. If you want to see someone standing atop a mountain, you'll need a telescope (or binoculars, etc.). As we know, this has nothing to do with distance, but instead with size. A counter-example is right in front of them: they can't see the person but they can see the mountain--both are equally distant.

The problem may be compounded by light pollution. The Hercules Cluster is invisible to the naked eye under LP but can be clearly seen through a telescope. So, naturally, the telescope is enabling them to see something very far away.

My usual response to the question is something along the lines of "the reason we can't see some things is because they are dim, not so much because they are far away. If our eyes were as big as this telescope, we'd be able to see them, too." But I don't think this is entirely satisfying to the people asking.

middbankrecra

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Re: "How far can your telescope see?"
« Reply #24 on: January 25, 2018, 09:28:45 PM »
I just usually tell folks how far a light year is and then how far away many objects are, and then how far they can see naked eye.  We always end up agreeing that it is much further than many politician's sight, even if the market has good seeing.

Cesar Lawhorn

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Re: "How far can your telescope see?"
« Reply #25 on: January 29, 2018, 09:38:56 PM »
My usual response is that it's not so much about how far, but how faint you can see. But I like the 1-12 billion light year answer.

Many years ago I attended a lecture on telescopes, and the speaker started out by summing it up; a telescope gives you light grasp and resolution. Those two talking points do fairly well in an outreach event.

micfullprovlo

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Re: "How far can your telescope see?"
« Reply #26 on: January 31, 2018, 05:04:24 AM »
Quote
I just usually tell folks how far a light year is and then how far away many objects are, and then how far they can see naked eye. We always end up agreeing that it is much further than many politician's sight, even if the market has good seeing.


People can be told how far a light year is, but it's really tough for the human mind to conceptualize just how huge the distances are when you're looking at a long string of zeroes. The best one I've heard so far goes something like this:

"Imagine the sun is an ordinary Major League baseball sitting on home plate at the Rogers Centre in Toronto. The Earth would be a ball-point-pen ball sitting about halfway out toward the pitchers' mound, and the outermost planets would be orbiting out beyond the outfield where the circular rails guide the retractable roof. Our nearest neighbouring star, Alpha Centauri four light years away, would be another baseball sitting on home plate at the Houston Astrodome."

Once people have digested that jaw-dropping sense of how puny humans really are, it's interesting to move on and talk about things that are a few hundred times further than Alpha Centauri (some nearby nebulae), a few thousand times further (some globular clusters), or a few million times further (some galaxies generally visible in an amateur telescope).

Sean Meyer

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Re: "How far can your telescope see?"
« Reply #27 on: January 31, 2018, 05:17:09 AM »
I like to do something similar on a slightly larger scale, using the Guy Ottowell "Thousand Yard Model". At this scale, the sun is the size of a 8" bowling ball (or 8" traffic light) and the earth is a 2 mm peppercorn about 74 yards away. The next nearest star would be as far away as ENGLAND is from the Midwest US at that scale, and that's just a close neighbor.

olaralal

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Re: "How far can your telescope see?"
« Reply #28 on: February 04, 2018, 10:28:10 AM »
Since the number of astronomical units in a light year (63,241.1) is almost equal to the number of inches in a mile (63,360), making the distance from the Sun to the Earth equal to one inch means that Proxima Centauri will be about 4.2 miles away.

Dave Mitsky

ovisimmus

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Re: "How far can your telescope see?"
« Reply #29 on: February 04, 2018, 12:12:59 PM »
This is a kind of neat scale-of-size visualization running from the quantum world to the entire universe:

http://htwins.net/sc...rdercolor=white