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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....
Actually exactly this is planned already.
There are radiotelescopes also, like Arrecibo (300m) or Effelsberg (100m).
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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No, because no matter how high resolution the pics are, it will never be enough to satisfy the moon hoax morons.
I suggest that we round up the hoaxers, and in an attempt to prove to them that we really did land on the Moon in 1969, send them to Tranquility base, let them out, and remove their helmets, because the visors would distort the view.
And with their dying breaths, you would see them mouth the words "movie set."
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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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Laser guide stars.
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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