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Global Internet Telescope Tops Hubble's Resolution
satorchi writes "
The Arecibo Observatory
together with the
European VLBI Network have used the internet to make a
real-time transatlantic synthesis telescope. Data from the individual telescopes was transfered via the internet, and processed in real time by the central processing station at the Joint
Institute for VLBI in Europe. 9 terabits were transfered during the 20 hour experiment, and the resulting synthesised telescope had a resolution of 20 milliarcseconds, about 5 times better than the Hubble Space Telescope (HST). This level of detail is equivalent to picking out a small building on the surface of the Moon!"
I don't know, but if you see something, the sceptics will claim the picture is fake.
Sadly I doubt it. If they weren't convinced by the reflectors, nothing will convince them http://www.lpi.usra.edu/expmoon/Apollo11/A11_Exper iments_LRRR.html
http://nssdc.gsfc.nasa.gov/database/MasterCatalog? sc=1969-059C&ex=4
The same reason Europe is building its own GPS-variant... to not depend solely on one country for something. Creating your own alternatives for important things is a good thing, you know.
- Leon Mergen
http://www.solatis.com
the hubble telescope gives you informations ...
in the visible and IR spectral range which
is completely different from radio astronomy
which is done here.
Comparing just the resolution of both methods
doesn't make much sense.
Slashdot articles should really be of a better
quality
Haven't we been using VLBI techniques for almost a decade? Or more?
The only thing I see in this story that is new is the fact that the VLBI data was sent over the internet, instead of the usual method of "Never underestimate the bandwitdth of a Fed-Ex truck full of terabyte data tapes." Otherwise, this is just announcing a new VLBI center.
we computer guys think we're geeky, but these stargazers make us look like a bunch of high school jocks.
Wut ? The use of AO is still largely confined to the longer wavelengths and over tiny, tiny fields of view compared to that of the whole instrument.
The absence of decent, bright, guide stars often limits performance, and the synthetic, laser induced, stars have their own problems.
And space based scopes can see when its cloudy on Earth.....
Steve
This was the funniest yet most insightful post I've seen in a long, long while. People who have their beliefs won't yield them no matter what we do to convince them. We could increase science funding so people can hopefully learn how to process information, but I doubt it. There's a huge crunch, at least in New York, on science teachers.
We should stop modding the guy "Funny" and "Informative" instead, since the former doesn't increase his karma. In fact, he should post a dumb comment and then mods should go and mod that up just to equalize his karma.
I am not TrollBridge's alterego.
Heh.
A NYC lawyer blogs. http://www.chuangblog.com/
That's another area where Hubble excels because it can integrate an area of sky for several orbits (Hubble Deep Field, for example), picking out very faint galaxies from nearly individual photons. These ground-based scopes, while integrating for long times, will probably integrate more scattered atmospheric light, and not be able to extract faint galactic signals from atmospheric noise nearly as well as Hubble.
make world, not war
Well, that's not true. Speckle interferometry can get to 70 milliarcseconds at 1.2 microns wavelength, and I'm working on an AO system that can get down to 85 milliarcseconds. What you may mean is that the Strehl ratio is nowhere near as good, which is very true.
If you are talking about the visible bands though, then it is true that hardly anyone has done well in that wavelength regime, and there I've heard the AEOS telescope on Maui can get halfway decent performance around a micron wavelength.
Dr Fish
Well, the 85 mas is for the MMT AO deformable secondary mirror system. I've reduced Ks band images with 90 mas full width at half maximum, and that's pretty repeatable. We're not the best by any means, and I've seen better images from the larger telescopes, but that's mostly due to larger aperture and having excellent seeing. (Nobody will showcase images from AO nights of 2 arcsecond seeing!)
The general definition of resolution is pretty fuzzy anyway (no pun intended) for AO systems, because the FWHM doesn't tell you the Strehl ratio of the image, which is what you really care about with these instruments. You can have poor image quality and yet still have a good FWHM measurement.
My original comment was on your fairly blanket statement about "nothing less than 100mas". I would have emphasised the lack of wide field correction, lack of UV wavelength coverage, and the problem with clouds as better reasons why AO cannot replace space telescopes.
AO is by no means a replacement for a space telescope (I would never claim that, and I work on an AO system!) but for certain science cases, it can do better than HST, partially because 8 meters of aperture beats a highly competitive 2m space telescope in light gathering capibility.
I've just had a thought rereading your comments - were you referring to purely visible (0.4 - 1.0 um) AO correction with 0.1 arcseconds? If you were, please accept my apologies - that'll teach me to RTF Comments :)
Dr Fish
To implement aperature synthesis you need to have the phase of the signal. Almost all optical recording devices just record the amplitude or intensity, because light waves vibrate at teraherz, i.e. beyond present day electronics, although we are closing in. Radio operates a megaherz which is easy to capture, record, transmit the phased signal.
If you have a full signal and high fidelity transimssion system you can send the actual light signals, with phase, to an analog inferometric synthesizer. This is presently being done at the ESO observatories simulating a optical mirror several hundred yards wide. This system has seen first light light, but is still in the developmental stage. Atmospheric distortion is a major issue.
"Having two scopes one mile apart, as far as resolution is concerned, is equivalent to having a single one-mile-wide mirror (in essence; the previous poster is correct in his argument about atmospheric distortions & other problems)."
No. Two scopes a mile apart gives you the equivalent of a scope a mile wide in one direction and a few meters wide in the other, with great resolution in one direction and normal in another. You need at least 3, and preferably many, arranged over a 2-d surface.
If you've ever seen any images produced by interferometric techniques you will note that most of them look like crap, with all kinds of odd distortions. This is something an astronomer can work around, but for nice images a single mirror/dish is superior.
I would say that, for the type of science that HST does (at the wavelengths that it does it), there is nothing on the ground that can match its resolving power.
*winces* sorry to be anal about it, but if you added "for visible wavelengths" to that then it would be on the money.
HST has an IR camera, and with that the AO ground observations on large telescopes beat HST in spatial resolution, period. The diffraction limit for HST at 1.65 microns is 200 mas, whereas for a 6.5m telescope, it is 64 mas. The PSF of HST is cleaner (i.e. follows a sinc pattern well) and stable than that of a ground based AO equipped telescope, but you can split binaries in the NIR on the ground that HST could not resolve. Because of the power law of the atmospheric turbulence, visible light AO is not being tackled, and so far there is no big push to work on it, as there is a lot to be done at near IR wavelengths where AO works a couple of orders better.
Thanks for your patience with my nitpicking - I do agree with your general view! AO in near IR is extremely competitive, but for visible and UV imaging, HST cannot be beat.
Dr Fish
It's also very important to note than the signals being combined in interferometry must be aligned to within a half a wavelength of tolerence (IIRC). So, for a radio signal, this is pretty easy. For optical interferometry, however, this is incredibly difficult and requires remarkably precise tuning of the optical path. This would be why optical interferometry is done on relatively small scales (although there are a number of projects out there working to build larger optical interferometers).