Author Topic: How big can we make a Telescope?  (Read 413 times)

Matthew Calhoun

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How big can we make a Telescope?
« on: December 28, 2017, 11:02:53 PM »
Throwing the weight issue out of the way, how big could we make a telescope before the light from the center would be too quick for the light from the edges to travel to the focuser and make an image distorted? Or could this even be an issue and I am just making a fool out of myself?



bermordliro

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Re: How big can we make a Telescope?
« Reply #1 on: December 29, 2017, 04:10:10 AM »
Fool!:^)Just kidding.

tingranseattters

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Re: How big can we make a Telescope?
« Reply #2 on: December 29, 2017, 05:49:53 AM »
"how big could we make a telescope before the light from the center....."

Hurt my head to think like that but...couple miles I guess.

Andy

Francisco Hossain

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Re: How big can we make a Telescope?
« Reply #3 on: December 29, 2017, 09:47:55 AM »
Kinda big, somewhere over the speed of light across outta do it.

Tyler King

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Re: How big can we make a Telescope?
« Reply #4 on: December 30, 2017, 10:11:03 AM »
BlueFalcon: google for Fermat's principle and see for yourself.

Levi Cruse

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Re: How big can we make a Telescope?
« Reply #5 on: January 03, 2018, 10:27:16 AM »
Quote
Throwing the weight issue out of the way, how big could we make a telescope before the light from the center would be too quick for the light from the edges to travel to the focuser and make an image distorted? Or could this even be an issue and I am just making a fool out of myself?

In optical terms, that's what the curvature of the optical elements has to do, it makes sure that all the light from the same part of the original 'beam' comes together at the focuser at the same time.

In a reflector, the curve makes the light from the 'edge' start reflecting back a bit sooner than the light from the centre.
In a refractor, the primary lens is thicker in the centre than at the edge, because that slows the light down more, and the thinner lens at the edge means that the light is slowed down for less time en-route

Of course, the curvature of the lens and mirror helps to bring the light to the same point, but bringing them together at the same time is needed to give a good image.

It's the same principle for Long Baseline Interferometry for Radio Telescopes, the signals from two radio telescopes separated by many kilometers are brought together and correlated so that they are brought together with the appropriate signal delay that they would have had if it was a single telescope dish.

So a valid question, and in response, we have used Very Long Baseline Intefrometry for radio telescopes that linked over thousands of km.

Dennis Collins

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Re: How big can we make a Telescope?
« Reply #6 on: January 09, 2018, 06:00:28 AM »
I'm thinking that it may be cheaper just to travel 'there'...

Jack Hillian

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Re: How big can we make a Telescope?
« Reply #7 on: January 10, 2018, 12:25:21 AM »
Looking to buy a 640' diameter pyrex blank.

szenawahle

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Re: How big can we make a Telescope?
« Reply #8 on: January 10, 2018, 11:42:02 AM »
How much is that gonna set you back?!

faubloginac

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Re: How big can we make a Telescope?
« Reply #9 on: January 11, 2018, 02:44:51 AM »
Funny

charnhoupito

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Re: How big can we make a Telescope?
« Reply #10 on: January 11, 2018, 06:20:22 AM »
I dunno. How big can a "gravitational lens" be?

Chris Young

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Re: How big can we make a Telescope?
« Reply #11 on: January 12, 2018, 01:09:34 PM »
Quote
I dunno. How big can a "gravitational lens" be?

I don't think a gravitational lens fits his clause about "before the light from the center would be too quick for the light from the edges to travel to the focuser and make an image distorted?"

unmoharib

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Re: How big can we make a Telescope?
« Reply #12 on: January 13, 2018, 09:46:09 PM »
Quote
Throwing the weight issue out of the way, how big could we make a telescope before the light from the center would be too quick for the light from the edges to travel to the focuser and make an image distorted? Or could this even be an issue and I am just making a fool out of myself?

Too Quick ???

For a parabolic mirror ...
http://montessorimud..._with_focus.png
the distance from the dotted line to focus point is the same ( the wave front is in-phase )

Largest telescope ... I assume you mean largest mirror?
Size of largest monolithic mirror?
Size of largest segmented mirror?
Size of largest interferometric set of mirrors? ( already exists and is located at the four "corners" of the earth )

Christopher Patel

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Re: How big can we make a Telescope?
« Reply #13 on: January 16, 2018, 03:02:55 AM »
Quote
Throwing the weight issue out of the way, how big could we make a telescope before the light from the center would be too quick for the light from the edges to travel to the focuser and make an image distorted? Or could this even be an issue and I am just making a fool out of myself?

How about the size of the moon. We actually used it to observe the sun with I think the Hubble, for the Venus transit.

So the moon is the reflector and the Hubble the eyepiece.

I have a design, carved into the side of a mountain thats a mile in dia.

asagnata

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Re: How big can we make a Telescope?
« Reply #14 on: January 25, 2018, 05:00:46 PM »
Quote
Quote

Throwing the weight issue out of the way, how big could we make a telescope before the light from the center would be too quick for the light from the edges to travel to the focuser and make an image distorted? Or could this even be an issue and I am just making a fool out of myself?

How about the size of the moon. We actually used it to observe the sun with I think the Hubble, for the Venus transit.

So the moon is the reflector and the Hubble the eyepiece.

I have a design, carved into the side of a mountain thats a mile in dia.
Very interestingconcept! But of course, you would have to have everything aligned perfectly. And if you messed your focal length up by a few nanometers you could have your focal point 100 miles too far or too close. But in theory, it would work.