A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Amateur Astronomy
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Tomorrow's Monster Telescopes



 
 
Thread Tools Display Modes
  #21  
Old March 11th 08, 09:40 PM posted to sci.astro.amateur
canopus56[_1_]
external usenet poster
 
Posts: 556
Default Tomorrow's Monster Telescopes

On Mar 11, 2:20*pm, L D'Bonnie wrote:
L D'Bonnie wrote:


snip all

L D'Bonnie wrote in news:47d59fdf$0$26249$6c5eefc5
@news.maximumusenet.com:

Perhaps my question should have been more along the lines of
Has nature imposed a limit to the maximum size a telescope could
be, where it would no longer be of any use to build bigger?
LdB


Looking at the question from a hypothetical prespective - free of the
engineering practicalities that limit materials - the answer is a
qualified no. For radio astronomy, there probably are no limits on
the
size of a useful telescopes.

For optical astronomy, the presence of interstellar and intergalactic
dust probably makes a theoretical limit on making a clear image - for
example - of a star or a planet in another galaxy. But, as we have
seen
in the past with microwave radio telescopes like COBE - even blurry
images of distant objects (the cosmic microwave background radiation)
-
can result in groundbreaking discoveries.

For radio astronomy, because of materials limits and for economic
efficiencies, some extremely large _synthetic_ telescopes are
currently
in use. These are much larger than you might intuitively expect.

Radio astronomers use very long baseline interferometry to create
synthetic telescopes many times larger than the size of the Earth.

http://en.wikipedia.org/wiki/Very_Lo...Interferometry

In the United States, the Very Long Baseline Array, a series of
interconnected radio telescopes -

http://en.wikipedia.org/wiki/Very_Long_Baseline_Array

- work together to create a synthetic radio telescope half the size
of
the Earth. The longest baseline (the diameter of the synthetic
aperture
of the radio telescope) is about 8600 kilometers.

The Europeans have a similar array - the Joint Institute for Very
Long
Baseline Interferometry in Europe (JIVE).

http://www.jive.nl/

When the two networks of radio telescopes work together - they form
the
GVLBI - the Global Very Long Baseline Array. This is a synthetic
radio
telescope with an aperture effectively the diameter of the Earth.

A larger synthetic radio telescope has been created in the past.
Through 2003, the Japanese space agency operated an orbiting radio
telescope called HALCA -

http://www.isas.ac.jp/e/enterp/missi...ca/index.shtml

- which had a maximum orbital altitude of about 24,000 kilometers.

When combined with Earth based arrays, HACLA created the largest
experimental aperture radio telescope ever known - one much larger
than
the Earth itself. As noted on the JAXA site, the Space VLBI telescope
-
even though it operated on radio wavelengths and not optically -
achieved an angular resolution "in these observations was [of] 0.3
milli-arcseconds in the 5 GHz frequency band, which is equivalent to
300
times the resolution of the Hubble Space Telescope."

http://www.isas.ac.jp/e/enterp/missi...a/achiev.shtml

But you do not need a multi-billion dollar space radio telescope to
create a truely massive synthetic telescope.

An intermediate-advanced amateur observing project is the detection
of
parallax shift of stars - and can be done will a 10 inch reflector
and
equatorial mount. In this type of synthetic telescope, a picture of
star is taken twice six months apart. The two images can be combined
to
see how the position of the star against the background stars has
changed.

http://en.wikipedia.org/wiki/Parallax#Stellar_parallax

This effectively creates a synthetic telescope with an aperture of
twice
the average radius of the Earth's orbit. The aveage radius of the
Earth's orbit is called an "astronomical unit" or "a.u." and is equal
to
about 150,000,000 kilometers. 2 a.u. is 300,000,000 kilometers.

For the future in optical astronomy, NASA has planned an orbiting
optical synthetic telescope - the Terresterial Planet Finder -

http://en.wikipedia.org/wiki/Terrestrial_Planet_Finder

- which, if realized, will be able to resolve planets orbiting nearby
stars. In 2007, the Bush administration and Congress defunded the
project for budgetary reasons - not technical reasons. The TPF's
future
remains unclear. The analogous European Space Agency proposal is
called
"Darwin", which is in the "assessment" stage of projects for
consideration after 2015.

http://sci.esa.int/science-e/www/are...cfm?fareaid=28

Finally, your pickup on the gravitational lensing was one that I
enjoyed -
using natural events - the chance positioning of large galaxies as a
"telescope".
I guess using a 200,000 light year diameter galaxy qualifies as the
largest "lens" ever used!

Hope that helps.

Peace - Canopus56

  #22  
Old March 11th 08, 11:08 PM posted to sci.astro.amateur
L D'Bonnie
external usenet poster
 
Posts: 15
Default Tomorrow's Monster Telescopes

canopus56 wrote:

For the future in optical astronomy, NASA has planned an orbiting
optical synthetic telescope - the Terresterial Planet Finder -

http://en.wikipedia.org/wiki/Terrestrial_Planet_Finder

- which, if realized, will be able to resolve planets orbiting nearby
stars. In 2007, the Bush administration and Congress defunded the
project for budgetary reasons - not technical reasons. The TPF's
future
remains unclear. The analogous European Space Agency proposal is
called
"Darwin", which is in the "assessment" stage of projects for
consideration after 2015.


Excellent reply, Thank You

Can you imagine one day, governments diverting military spending
towards science instead of the other way.

LdB

  #23  
Old March 12th 08, 08:12 AM posted to sci.astro.amateur
Paul Schlyter[_2_]
external usenet poster
 
Posts: 893
Default Tomorrow's Monster Telescopes

In article ,
L D'Bonnie wrote:

If I understand correctly there is no theoretical maximum size,
that if you can build it bigger it will have more resolution.


If nothing else, at least the size of the universe ought to be a
theoretical maximum size of a telescope.... :-) ....perhaps some
people would consider that a practical rather than a theoretical
limit....

I suppose the answer to my question was partially answered in the
another article in the same magazine (p. 16) A Double Einstein
Ring. The galaxy SDSS J0946 is acting as a lens. All you would
have to do is to devise a way to reach out and focus it.

So it seem if professional astronomers actually do suffer from
aperture fever (or envy), there can be no cure for them. They are
doomed to be forever anticipating the construction of the next
larger telescope.

LdB

Indeed..... check out:

http://stjarnhimlen.se/bigtel/LargestTelescope.html




--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stjarnhimlen dot se
WWW: http://stjarnhimlen.se/
  #24  
Old March 12th 08, 08:12 AM posted to sci.astro.amateur
Paul Schlyter[_2_]
external usenet poster
 
Posts: 893
Default Tomorrow's Monster Telescopes

In article ,
canopus56 wrote:

Finally, your pickup on the gravitational lensing was one that I
enjoyed -
using natural events - the chance positioning of large galaxies as a
"telescope".
I guess using a 200,000 light year diameter galaxy qualifies as the
largest "lens" ever used!


That "lens" is much larger than the galaxy itself! It works through the
gravity from the galaxy which bends the light rays - and the gravity from
the galaxy extends well beyond the physical size of the galaxy itself,
making the effective size of the "lens" perhaps a few million light years
large!

And, in contrast to glass lenses, a gravitational lens is completely
achromatic! I strongly doubt a gravitational lens could be used well
as a telescope though, because it probably suffers from several other
horrible aberrations....





--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stjarnhimlen dot se
WWW: http://stjarnhimlen.se/
  #25  
Old March 12th 08, 08:12 AM posted to sci.astro.amateur
Paul Schlyter[_2_]
external usenet poster
 
Posts: 893
Default Tomorrow's Monster Telescopes

In article ,
L D'Bonnie wrote:
canopus56 wrote:

For the future in optical astronomy, NASA has planned an orbiting
optical synthetic telescope - the Terresterial Planet Finder -

http://en.wikipedia.org/wiki/Terrestrial_Planet_Finder

- which, if realized, will be able to resolve planets orbiting nearby
stars. In 2007, the Bush administration and Congress defunded the
project for budgetary reasons - not technical reasons. The TPF's
future
remains unclear. The analogous European Space Agency proposal is
called
"Darwin", which is in the "assessment" stage of projects for
consideration after 2015.


Excellent reply, Thank You

Can you imagine one day, governments diverting military spending
towards science instead of the other way.


That happened, in a way, during the space race of the 1960's. The
alternative to the space race would probably have been an even bigger
nuclear arms race....

LdB



--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stjarnhimlen dot se
WWW: http://stjarnhimlen.se/
  #26  
Old March 12th 08, 02:41 PM posted to sci.astro.amateur
Helpful person
external usenet poster
 
Posts: 251
Default Tomorrow's Monster Telescopes

On Mar 11, 4:40*pm, canopus56 wrote:


For the future in optical astronomy, *NASA has planned an orbiting
optical synthetic telescope - the Terresterial Planet Finder -

http://en.wikipedia.org/wiki/Terrestrial_Planet_Finder

Peace - Canopus56


As I read it this is not a synthetic aperture telescope. At optical
wavelengths this is way beyond our technology.
  #27  
Old March 12th 08, 08:38 PM posted to sci.astro.amateur
Dennis Woos
external usenet poster
 
Posts: 559
Default Tomorrow's Monster Telescopes


The obvious limit is when the telescope size becomes so large that it
contains a significant percentage of the universe's mass.


I don't think that a mirror, or telescope, needs to have much mass at all.
Currently, most of the mass is in the material (glass) holding the
reflective surface and the mechanism for pointing this mass. The mass of the
reflective coating must be very, very small. In the future, it may be
possible to produce a mirror with not much more mass than this coating. Is
it a violation of the laws of nature to do away with the reflective material
altogether and collect and focus the light some other way, e.g.
electromagnetically?

Dennis


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
preview of tomorrow's spacewalk Jim Oberg Space Station 0 February 21st 07 11:41 PM
prominences for tomorrow's eclipse ? nytecam UK Astronomy 6 October 5th 05 03:56 PM
solar proms for tomorrow's eclipse ? nytecam Amateur Astronomy 0 October 2nd 05 10:17 AM
BBC R4 tomorrow's afternoon play "Kepler" (wednesday 11th at 14:15) Robin Leadbeater UK Astronomy 0 August 10th 04 03:39 PM
Interferograms for Four High Quality Telescopes and Two Commercial Telescopes Edward Amateur Astronomy 3 January 11th 04 02:02 AM


All times are GMT +1. The time now is 03:02 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.