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World's Largest Virtual Optical Telescope Created
erice writes "Astronomers in Chile linked four telescopes together to form a single virtual mirror 130 meters in diameter. Previous efforts had linked two telescopes but this is the first time that all four had been linked. 'The process that links separate telescopes together is known as interferometry. In this mode, the VLT becomes the biggest ground-based optical telescope on earth. Besides creating a gigantic virtual mirror, interferometry also greatly improves the telescope's spatial resolution and zooming capabilities.'"
the big problem I think is atmospherics. Getting two scopes to sync is the easy bit, getting them to dance out shimmer is difficult - the idea of interferometry (FYI) is to separate two points - difficult to do if they're moving in different directions in two (or four) locations at the same time. I reckon the best they could do here is to apply some sort of real time or maybe even predictive correction to the raw data (wind sensors?). Job even harder if the sensors are located a continent or two apart...
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The coolest thing I learned about the VLT is that it uses a laser to excite sodium particles 90km up in the atmosphere which creates a very faint 'star' at a very well-known distance. This reference point is used to make tiny adjustments to the mirrors to correct for atmospheric turbulence. These telescopes are not continents apart, they are all at the Paranal observatory in Chile. The light from each telescope is routed underground through equal-length tunnels to a central point to make one GIANT image. From wikipedia, "when all the telescopes are combined, the facility can achieve an angular resolution of about 0.001 arc-second. This is equivalent to roughly two metres at the distance of the Moon."
It's not the equivalent of a 130-meter diameter mirror; it's the equivalent of that mirror with all but four 8.2-meter diameter pieces of it blacked out. Yes, you can get a sharper image using interferometry, but your total light-gathering area is 211 square meters, not 13,273 square meters. That's going to affect exposure times. But still, it's cool. :)
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I think Keck's got near-IR interfometry working. I very strongly suspect VLT is doing near-IR as well, but the article doesn't say. And this use of an optical chip instead of mirrors... dunno.
I'm still waiting for the "Ohana" project that's supposed to link Keck 1+2, Subaru, Gemini, and maybe some of the 3-meter-class scopes near them through single-mode fiber. Maximum baseline if they build that? 800 meters, if I recall.
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Why not plan for an array at one of the Lagrange points?
Just asking....
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Can we get to see the Apollo landing sites? Some sharp images this time?
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There are radiotelescopes also, like Arrecibo (300m) or Effelsberg (100m).
I heard on NPR the other day a story about Roger Angel, U. Arizona mirror guru, who's making 27-footers for installation in Chile by, I think it was, 2020. The amazing part is casting to that accuracy -- without exact uniformity. These 27-foot mirrors have to focus slightly off-center. Here's the transcript: http://m.npr.org/news/Science/145837380
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Your referring to the Dawes's resolution limit [arc sec] = 116 / Aperture Diameter [mm] (for green light), it's actually the edges that contribute the most to resolution, where the glass in the middle increases the light gathering ability more and the glass in the center usually doesn't do anything. As the glass gets bigger, the cost increases exponentially. The lack of light gathering is easy to compensate by increasing the exposure time.
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the big problem I think is atmospherics. Getting two scopes to sync is the easy bit, getting them to dance out shimmer is difficult - the idea of interferometry (FYI) is to separate two points :-)
Each telescope has its own adaptive optic correction system, which takes care of the atmospheric aberrations within its own field of view. The separate telescopes' corrected images are then combined interferometrically, plus and additional A-O step to account for atmospheric differences between telescopes. I'd call it all "magic" except that I worked on A-O systems for 20 years
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Since I don't know I'll ask...
Can this scale up to multiple scopes, and does this need a minimum size scope ?
I'm asking for the following reason: ...
I think it would be a great service to mankind if, people that own telescopes could hook up the telescopes every now and then to a central platform and let the computers observe the local solar system for possible unknown items in space. given, I think that I think the idea is years away, I would like to start tinkering with the idea.
Heck, we now have DIY CNC machines, people whom will help ( for reasonable prices ) design circuit boards, and places to swap equipment, I think this might be something I could start working on for the next 5 to 10 years.
what I picture is a centralized server receiving images from 100 or 200 scopes from all over the world, and just cataloging them, then they run the comparison via a seti@home type platform. the centralized server send location data of where to look...
Again I am just dreaming out loud, but if could even work with 12 inch platforms, it just might be a wonderful tool for local discovery.
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"Besides creating a gigantic virtual mirror, interferometry also greatly improves the telescope's spatial resolution and zooming capabilities."
Should read:
"Interferometry greatly improves the telescopes' spatial resolution."
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I understand that (one of) the designs for the TPF was for four optically linked telescopes spanning about(?) 100m that using interferometry/optical nulling/coronagraphs could isolate enough light from a planet to get its spectrograph and thus determine if it (might) have life.
Of course the TPF was not only supposed to be in space but in DEEP space (in Jupiter orbit, at the trojan point?) so as to avoid the zodiacal light but is this overcome by the MUCH greater light capturing ability of these giant 'scopes? Or are they too deep in our own atmosphere to be able to get any sort of spectrographic reading of another planet's atmosphere at any wavelength? (Is there any mountain on earth tall enough?)
Thank you for the information
here is the link for astronomical interferometry http://en.wikipedia.org/wiki/Astronomical_interferometer
it seems that the application for this is amazingly great for light year distances and beyond, I am just wondering if on the smaller scale ( with smaller telescopes ) would it work on a solar system scale.
but hey this is a start
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http://xkcdsucks.blogspot.com/2011/08/comics-uh-941-943-maybe-triple-feature.html
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And X-ray telescopes in orbit (the Chandra X-Ray Observatory) and gamma ray telescopes in orbit (the Fermi Gamma-Ray Space Telescope) and on the ground (the MAGIC-I and II atmospheric imaging Cherenkov telescopes).
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A-O ? So that would be like virtual adaptive optics (as in lens corrections executed in mathematics) ?
I think what you're trying to point out is that the TFS is misleading, if the submitter intended to imply that interferometry improves both aperture and resolution. With interferometry, of course, one gets the resolution of the baseline (in this case 130m), but the aperture remains the same as the telescopes themselves. Meaning that one can improve the resolution of images, but not their sensitivity -- the light photons that fall onto the ground between the telescopes are still lost, whether or not interferometry is being used.
A-O is "real" adaptive optics: measure the wavefront error and move some physical object, e.g., deformable mirrror, to correct the phase errors. It takes a bunch of math, but depends on fixing the light before it becomes an image.
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If we could have well synchronized time (down to a small fraction of observed wave's period), and sensors that could heterodyne the incoming optical signal, then we could simply frequency-shift the optical signal, digitize the I and Q (preserves phase and amplitude), record it with the timestamps, and do interferometry completely offline. No adaptive optics needed, it'd be all done digitally. It's done that way for some radioastronomy and is no big deal, the only problems are technical when you think of doing it for optical observations. As in: we're not there yet to do optical I-Q heterodyning, but perhaps we're close enough. Once that becomes mainstream, 130m equivalent diameter will be nothing noteworthy, we'll be probably able to observe moon at sub-millimeter resolutions and it'd be amateurs doing that. My expectation is that it'll be possible in well less than a 100 years.
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Why not get a couple thousand 10" reflecting telescopes on digital servo mounts (~$1,500 each), hook them up to HD web cams (~$1,500 each), and use netbooks (~$300 each) with unlimited data plans (~$500/yr) to connect to database that uses a volunteer-based distributed computing network to process the data using inteferometry? You'd effectively have a telescope with a mirror the size of the Earth for about the cost of a professional level telescope. It would be orders of magnitude more powerful than anything else we could build. I still have no idea why this hasn't been built yet.
It is my understanding that by seperating the detectors over large distances in space or time, it makes it easier to detect and correct for atmospheric abberations. Which is one of the reasons interferometers were built in the first place.
No. Paranal is 24 d 37'; they should see down to 65d 23', but adding a few degrees for atmosphere and the pointing of the telescopes, they can see any part of the sky from 90 S to roughly 60 N, which is 87% of the whole sky.