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World's Largest Virtual Optical Telescope Created

Soulskill posted more than 2 years ago | from the very-very-large-telescope dept.

Space 57

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.'"

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Optical interferometry? (0)

Anonymous Coward | more than 2 years ago | (#38925187)

The last I knew (4-5 years a ago) Keck was still struggling to get optical interferometry to work well, and those mirrors have a smaller baseline. Has this technique matured since then?

Re:Optical interferometry? (3, Interesting)

Tastecicles (1153671) | more than 2 years ago | (#38925259)

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...

Re:Optical interferometry? (5, Informative)

Jesse_vd (821123) | more than 2 years ago | (#38925303)

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."

Re:Optical interferometry? (-1)

Anonymous Coward | more than 2 years ago | (#38925445)

The Seattle Animal Control folks have done a study and determined that
last year:

174,000 cats in Seattle produced 5.6 million pounds of cat shit (32 pounds
a year per cat).

I would have thought it would be more...

Re:Optical interferometry? (-1)

Anonymous Coward | more than 2 years ago | (#38925837)

That IS somewhat disappointing.

Re:Optical interferometry? (-1)

Anonymous Coward | more than 2 years ago | (#38926003)

Tyxt33358dggyf

Re:Optical interferometry? (3, Interesting)

Ambitwistor (1041236) | more than 2 years ago | (#38926609)

Laser guide stars [amusingplanet.com] .

Re:Optical interferometry? (2)

cellocgw (617879) | more than 2 years ago | (#38926529)

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 :-)

Re:Optical interferometry? (1)

OeLeWaPpErKe (412765) | more than 2 years ago | (#38928271)

A-O ? So that would be like virtual adaptive optics (as in lens corrections executed in mathematics) ?

Re:Optical interferometry? (1)

cellocgw (617879) | more than 2 years ago | (#38929959)

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.

Re:Optical interferometry? (2)

onepoint (301486) | more than 2 years ago | (#38926575)

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.

Re:Optical interferometry? (0)

Anonymous Coward | more than 2 years ago | (#38926723)

Theoretically, yes. Practically, astronomical interferometry (there's a Wikipedia article on that, might want to read it for additional information) is incredibly complex and thus expensive. It begins with the problem that you need fairly good adaptive optics, and goes on to require optical waveguides (likely fibers or tunnels) of exactly equal length.
Still, I agree that this would be awesome for amateur astronomy, and some enthusiasts should definitely build a prototype. :)

Re:Optical interferometry? (1)

onepoint (301486) | more than 2 years ago | (#38926931)

Thank you for the information
here is the link for astronomical interferometry http://en.wikipedia.org/wiki/Astronomical_interferometer [wikipedia.org]

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

Onepoint

Re:Optical interferometry? (2)

tibit (1762298) | more than 2 years ago | (#38932153)

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.

Re:Optical interferometry? (1)

sudonim2 (2073156) | more than 2 years ago | (#38935987)

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.

Re:Optical interferometry? (4, Interesting)

Shag (3737) | more than 2 years ago | (#38925325)

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.

Re:Optical interferometry? (0)

Anonymous Coward | more than 2 years ago | (#38925657)

Many people probably know what the VLT is. But it still should be mentioned that this is not some Chilenian telescope, but the biggest telescope aray funded by the European Union's ESO.

Re:Optical interferometry? (0)

Anonymous Coward | more than 2 years ago | (#38926261)

Chilean, Chilean, not Chilenian (are you Germanian?). and yes, the telescopeas and operation are funded by ESO (this is decoupled from the European Union), and the site was donated by Chile.

Re:Optical interferometry? (0)

Anonymous Coward | more than 2 years ago | (#38930377)

Sorry, just wanted to make clear that the VLT is playing in the same league as Keck.
Your guess about my origin was correct. Are we the only ones adding this n in between?

"Besides", or by? (0)

Anonymous Coward | more than 2 years ago | (#38925281)

TFS:

Besides creating a gigantic virtual mirror, interferometry also greatly improves the telescope's spatial resolution and zooming capabilities.

Uh, isn't that exactly what we gain from a large aperture?

Also, good job making optical interferometry work -- that's some tough shit.

Re:"Besides", or by? (2)

budgenator (254554) | more than 2 years ago | (#38926471)

Your referring to the Dawes's resolution limit [wikipedia.org] [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.

Re:"Besides", or by? (0)

Anonymous Coward | more than 2 years ago | (#38926747)

Your referring to the Dawes's resolution limit [wikipedia.org] [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.

I'm actually talking about the Rayleigh criterion [wikipedia.org] , of which Dawes's limit is merely an empirical approximation for optical wavelengths. And I never said anything about filled-aperture and the sparse-aperture curse, because I was addressing the assertion we get larger aperture AND improved resolution, when in reality the large aperture is responsible for the improved resolution.

So your reply, while true, has fuck-all to do with what I said.

aperture vs. resolution (1)

dtmos (447842) | more than 2 years ago | (#38929495)

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.

Re:aperture vs. resolution (0)

Anonymous Coward | more than 2 years ago | (#38930209)

No, it also increases aperture -- the aperture IS 130m across, it's just sparse. Saying that "the aperture remains the same" is like saying that aperture masking turns a 10m aperture into a cm-range aperture. Do you people not understand the concept of a sparse aperture?!

Re:aperture vs. resolution (1)

dtmos (447842) | more than 2 years ago | (#38932477)

Well, I don't know, Mr. AC. To which "people" do you refer? Most "people" I know in astronomy define an "aperture" in the same way Wikipedia does [wikipedia.org] :

[T]he aperture stop is the stop that determines the ray cone angle, or equivalently the brightness, at an image point.

In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself. For example, in a telescope the aperture stop is typically the edges of the objective lens or mirror (or of the mount that holds it). One then speaks of a telescope as having, for example, a 100 centimeter aperture. [emphasis added]

Most astronomers I know actually would, in fact, tell you that aperture masking turns a 10m aperture into a cm-range aperture, since the sensitivity of the resulting telescope would be that of one having a much smaller diameter. That's how most cameras work . . . f-stops, anyone?

Strictly speaking, the usual use of the word "aperture" in astronomy actually means, "diameter of a circular aperture have equivalent area," since that telescope would be of equivalent sensitivity. Saying the Chilean interferometer has an aperture of 130m is saying that the diameter of its aperture stop is 130m, which is saying that it has the sensitivity of a solid 130m-diameter aperture, which isn't true. In fact, without assuming a shape and orientation for the mask (aperture stop), saying a telescope has an aperture of X meters is a meaningless statement.

There may be an astronomical context in which the strict definition of aperture, as you are using it, is common, but I'm unaware of it. Perhaps those doing the interferometric mathematics define it this way.

Ehhh, not exactly. (5, Informative)

Shag (3737) | more than 2 years ago | (#38925317)

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. :)

Re:Ehhh, not exactly. (3, Interesting)

jgardia (985157) | more than 2 years ago | (#38926281)

Of course, you don't have the light gathering capacity of a 130m telescope, but you have the spatial resolution of a130m telescope.

Re:Ehhh, not exactly. (2)

alreaud (2529304) | more than 2 years ago | (#38926877)

Just what one needs to image the black hole at the center of the Milky Way. If they can get the timing right, between this set of 4 telescopes operating as one, the Keck telescopes in Hawaii, and the Spitzer IR Space Telescope, we could have a virtual telescope in the IR band that is easily 30,000 km wide.
http://www.keckobservatory.org/ [keckobservatory.org]
http://www.spitzer.caltech.edu/ [caltech.edu]

Btw: This idea increased spatial resolution using very long baseline interferometry is why it would be worth a few billion dollars to send multi-spectral moderate aperture telescopes to the L4 & L5 points, IMHO.
http://en.wikipedia.org/wiki/Lagrangian_point [wikipedia.org]

Re:Ehhh, not exactly. (0)

Anonymous Coward | more than 2 years ago | (#38930649)

...you have the spatial resolution of a130m telescope.

This is almost, but not quite, true. If you have two telescopes separated by 130m, and observe for long enough to compensate for your limited light-gathering capacity, you get an image like that of a 130m telescope - plus some awkward distortions. As you build additional telescopes within that 130m, those distortions decrease. In the limiting case, if you build wall-to-wall telescopes, they go away entirely - because what you've got is the 130m telescope we were using as a comparison.

This is why they're using four telescopes, rather than just two. With four, plus a bit of smart signal-processing to minimise the distortions, their image will be almost as sharp as that from a 130m telescopes.

Radio astronomers, incidentally, have been doing this stuff for a while longer. They build arrays of 27 [wikipedia.org] or 36 [wikipedia.org] telescopes, to minimise distortions. And to reduce costs - it's more expensive to build one big telescopes than to build a bunch of little ones with the same total light-gathering area.

This is cool, but.... (1)

rts008 (812749) | more than 2 years ago | (#38925471)

Why not plan for an array at one of the Lagrange points?

Just asking....

Re:This is cool, but.... (0)

Anonymous Coward | more than 2 years ago | (#38925863)

Because a) it's a lot harder to get to a Lagrange point that it is to walk up a hill on the planet and b) why not just build one giant (presumably segmented) mirror and put that at the L point?

Re:This is cool, but.... (2)

Zorpheus (857617) | more than 2 years ago | (#38926095)

Why not plan for an array at one of the Lagrange points?

Just asking....

Actually exactly this is planned already [wikipedia.org] .

Re:This is cool, but.... (1)

WillDraven (760005) | more than 2 years ago | (#38926459)

Why not plan for an array at one of the Lagrange points?

Just asking....

Actually exactly this is planned already [wikipedia.org] .

If by planned you mean considered and then abandoned..

The study of this proposed mission ended in 2007 with no further activities planned.

Ever since I heard about interferometry I thought we should put some satellites at far distant points (perhaps Earth's L2 and L3 points, with a repeater at L4 or L5 so the signal can get around the sun) and get some really impressive pictures of distant objects.

Re:This is cool, but.... (0)

Anonymous Coward | more than 2 years ago | (#38926485)

According to the link, the idea was merely studied... not planned. In fact, it says that additional studies are needed in order to determine if it's even possible to control distance to the micron/nanometer accuracy needed.

obligitory xkcd (0)

Anonymous Coward | more than 2 years ago | (#38925485)

this one springs to mind:

xkcd.com/941

Wrong Tilte (0)

Anonymous Coward | more than 2 years ago | (#38925683)

A telescope is optical as far as I know. The thread should be "Largest Virtual Telescope" without the misleading optical term.

go ahead, mod down this comment further, I don't care any more...

Re:Wrong Tilte (2)

jgardia (985157) | more than 2 years ago | (#38926285)

There are radiotelescopes also, like Arrecibo (300m) or Effelsberg (100m).

Re:Wrong Tilte (1)

careysub (976506) | more than 2 years ago | (#38927811)

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).

Apollo Landing Sites (1)

AHuxley (892839) | more than 2 years ago | (#38925869)

Can we get to see the Apollo landing sites? Some sharp images this time?

Re:Apollo Landing Sites (2, Insightful)

bmo (77928) | more than 2 years ago | (#38926511)

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."

--
BMO

Re:Apollo Landing Sites (1)

bmo (77928) | more than 2 years ago | (#38926769)

Follow-up for resolution limit for a 130M telescope looking at objects on the Moon.

Best resolution = distance to object * wavelength / diameter of mirror

Best resolution = 400,000,000M * 500nm / 130M

1.5M.

You'll get fuzzy images regardless.

For what the Hubble could see, just substitute 2.4 for the mirror diameter. You get roughly 80 meters across. This is why Hoaxers are morons when they say "just point Hubble at the Moon."

--
BMO

Re:Apollo Landing Sites (0)

Anonymous Coward | more than 2 years ago | (#38931669)

no no send them to a remote Arizona desert site that LOOKS JUST LIKE Tranquility Base and let them die in the heat as they crow about being right.

Re:Apollo Landing Sites (1)

tlhIngan (30335) | more than 2 years ago | (#38932945)

No, because no matter how high resolution the pics are, it will never be enough to satisfy the moon hoax morons.

And remember, if it's TOO high resolution, it'll just scream "PHOTOSHOP!" because the lander photo will be less blurry than the moon photos beside it.

Re:Apollo Landing Sites (1)

wisebabo (638845) | more than 2 years ago | (#38926715)

Actually, I think(?) that a giant scope like these could never look at the Moon (and maybe Venus, the next brightest object in the night sky) is because the light gathering capability would burn the sensors.

I mean the light amplification from something 8m across down to about a centimeter(?) must be close to a million fold. So imagine moonlight a million times brighter. Gives new meaning to the expression "blinded me with science".

But maybe they put a piece of cardboard in front of the mirror and punch a little hole in it.

Neutral density filter Re:Apollo Landing Sites (0)

Anonymous Coward | more than 2 years ago | (#38930739)

How about a neutral density filter?
(I have no idea how these telescopes really work)

trollko8e (-1)

Anonymous Coward | more than 2 years ago | (#38926037)

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27ft mirrors, heard on NPR (1)

garthsundem (1702946) | more than 2 years ago | (#38926325)

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 [npr.org]

It proves that Hubble Telescope is obsolete. (0)

Anonymous Coward | more than 2 years ago | (#38926507)

It proves that the Hubble Telescope is obsolete.

Re:It proves that Hubble Telescope is obsolete. (0)

Anonymous Coward | more than 2 years ago | (#38927391)

It proves that the Hubble Telescope is obsolete.

Since this telescope is in Chile, it can only observe the portion of the sky visible from the southern hemisphere.

The Hubble Telescope can observe anywhere in the southern and northern hemispheres.

Just sayin'.

Re:It proves that Hubble Telescope is obsolete. (1)

fremsley471 (792813) | more than 2 years ago | (#38936557)

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.

minor edit (1)

ArcSecond (534786) | more than 2 years ago | (#38926647)

"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."

Re:minor edit (1)

plover (150551) | more than 2 years ago | (#38926843)

Here it is straight from CSI: VLT

"It looks like the Chileans ..."
[puts on sunglasses]
"zoomed and enhanced."
YEEAAAHHHHHHHHH!!!

Will this be able to replicate the TPF? (1)

wisebabo (638845) | more than 2 years ago | (#38926653)

(Terrestrial Planet Finder)

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?)

Congrads.... (1)

butilikethecookie (2566015) | more than 2 years ago | (#38929753)

you can now watch alien women undressing....

The Obvious Thing to Do (1)

sudonim2 (2073156) | more than 2 years ago | (#38935967)

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.
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