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#21
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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
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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
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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
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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
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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
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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
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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 |
#28
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Tomorrow's Monster Telescopes
Helpful person wrote in news:dba646c5-8018-42a6-9177-
: As I read it this is not a synthetic aperture telescope. At optical wavelengths this is way beyond our technology. Bad use of language on my part. By "synthetic" telescopes, I was meaning "synthetic image" - two images taken by two telescopes at two locations and digitally combined. - C P.S. - Probably should have mentioned interferomtery of the surface of Betelguese Coast and the Keck interfermoter as examples. http://www.mrao.cam.ac.uk/telescopes/coast/betel.html http://planetquest.jpl.nasa.gov/Keck/keck_index.cfm -- Posted via a free Usenet account from http://www.teranews.com |
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