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100 Meter OWL Telescope Project
mindpixel writes: "The European South Observatory (my employer) is getting VERY serious about building the OWL (OverWhelmingly Large) 100 meter telescope. Check out this new site dedicated to the project. You can see some cool diagrams of what the OWL telescope will look like and some simulated images here." For more about telescopes of unusual size, you might read McKinstry's interview last year.
For the same amount of money you can make awesome pictures of Africa without any national debts or children starving.
Really, the costs going to these space projects is just insane. Where are our priorities?
One thing which I've been wondering about VLT is the usage of just digital imaging (FORS1, etc)...or at least I haven't noticed any VLT cameras using traditional film (correct me if I'm wrong). I know that CCDs are great for making photometric measurements because of their linearity, but their resolution is nothing compared to large photographic plates used in older cameras. For example, FORS1 is just 2048x2048.
Well, ok, camera resolution might not be so important in most research, but I would imagine that doing the Palomar sky survey (hundreds of huge plates) with CCDs would be impossible (it would probably require trillions of pictures). ...And the best space poster pictures are still the ones taken with the Palomar 5m. ;-)
So, how are surveys made now or in future, with CCDs or plates? Are surveys or other hi-res imaging still relevant?
[I'm eagerly waiting for a job decision from ESO at Garching, should come next week. It would be great to get to mess up^H^H^H^H^H^H^Hdevelop the computer systems there. ;-)]
Not quite solid, try made of hexagonal mirrors approx 2m across. It would be a huge pain in the ass to make a 100m diameter mirror, not to mention uneconomic. Thats why they plan to have it tiled. But all the tiles do make up the mirror for one large telescope. Cheers
This doesn't apply to telescopes described in the article, but there's a method for removing the light of a star in order to see dimmer companions (such as planets) which is called nulling interferometry.
An interferometer is an instrument with two telescopes, which uses the wave nature of light to combine them. When you separate 2 telescopes by say 100 meters and combine their light properly, you get the apparent resolution of a 100m telescope (minus the light gathering power and the cost).
A nulling interferometer doesn't try to combine the wavelengths at the same place (think reinforcing the wave you're getting from the object). Instead it delays one of the the waves by 1/2 wavelength, so when the two are combined, they cancel each other out (at least in the center).
So the light of the star is "nullified" while you can still measure the light coming from very close by.
The technique has been demonstrated in the lab, but I don't believe it has been used in practice. It may be used in some astronomy satellites in the future.
Doug
Venn ist das nurnstuck git und Slotermeyer? Ya! Beigerhund das oder die Flipperwaldt gersput!
Everytime you read about the newest development in telecscope technology, it's given an outrageous name describing how large it is. I remember when the Very Large Telescope, or VLT, came about. Now we have OverWhelmingly Large? This is complete craziness. We've got Large, Very Large, OverWhelmingly Large, and the ultimate which will probably never be developed, My Penis!
For the price of one small space telescope (HST mirror is only 2.4m in diameter) you can build the largest earth-based telescopes ten times over (the ESO VLT, 4 8m telescopes working as an array will, when fully operational in 2003-2004 have cost maybe 1/5 of what Hubble has cost until now). Furthermore, in visible light, earth-based telescopes are already producing images as sharp as, and even sharper than Hubble. At the time the HST was conceived, Adaptive Optics, which can eliminate most atmospheric turbulence, was still a US Military classified technology). The only short-term reasons for building space telescopes are: 1) observing in wavelengths absorbed by our atmosphere (like much of the IR and UV spectrum) 2) Getting spectra of earth-like planets surrounding other stars, this would require a space-based interferometer, because the earth probably isn't a sufficiently stable base to do this type of observations...
The problem is that angular resolutions of telescopes are given for separating two objects of the same maginitude. A star is so damn bright compared to any orbiting planet (probably more than 1,000,000,000 times brighter) that, if the image is taken with an exposure time that would make the planet visible, the atmosphere will spread the star to many arc secs, even with the best adaptive and active optics. I think OWL would also have this problem.
I don't know exactly why Hubble can't see such planets. Probably its angular resolution is still not good enough. Also, CCDs don't always behave nicely when they are grossly overexposed, as the CCD would be if there's a planet in one pixel and its star two pixels away.
Btw, Alpha Centauri is a multiple star, and the close component stars probably can't have stable planets. Proxima Centauri (one of the components) is farther away from the others and might have planets (I guess).
The Sloan Digital Sky Survey is using CCDs to map one quarter of the entire sky, in five passbands. Its main camera uses a mosaic of 30 2048x2048 CCDs to cover an area about 2.5 degrees across (although there are gaps between the chips). Other mosaic cameras have even more pixels.
Future ground-based surveys will use electronic detectors, not photographic plates. The increased sensitivity and linearity of electronic detectors, plus their inherent digital output, make them far superior to plates.
Michael Richmond "This is the heart that broke my finger."
mwrsps@rit.edu http://stupendous.rit.edu
What are the benefits of having an Earth-bound, optical telescope? Or rather, what can a larger optical telescope find better from Earth that we can't already find on other wavelengths and from other venues (i.e. The Hubble)?
If there are no advantages here, is it more cost-effective, or what?
Chris: What you should actually ask is what advantage does a space based telescope have over a ground based telescope? The only thing you gain from being in space for an optical telescope is better image quality due to lack of atmospheric turbulence. By for every other measure (maintenance, support, materials, etc.) being in space is much, much more expensive and limited. Which is why the Hubble and it's 2.4 meter primary cost a number of times more than the projected cost of of the 100 meter OWL. Recent advances in computer technology (adaptive and active optics) have greatly reduced the advantage that being in space provides at optical wavelengths. For some non-optical telescopes (x-ray, IR, gamma ray) there will always be an advantage to being in orbit.
Space based and ground based telescopes compliment each other. Right now, the Hubble's primary mission is that of a scout... it finds targets for the VLT (which I operate)... the Hubble's mirror is small and exposure times are limited by cosmic rays... the ground based VLT is much better at getting science data once the Hubble finds the target.
The next space telescope will be the NGST (Next Generation Space Telescope) which will be about the size of a single VLT telescope (we have 4 here in Chile) and it again will act as a scout for the OWL.
On the other hand, it is far away relative to low Earth orbit. It is expensive to get there and, once there, manned missions to repair and upgrade it would be, at this time, out of the question. Hubble has benefitted massively from such upgrades, from the optics correction package to the replaced gyros and computer upgrade. You could do without them, but it's something to be considered.