Engineering the 30-Meter Telescope 64
yyzmcleod writes "When completed in 2018, the Thirty Meter Telescope (TMT) will be the world's largest and most powerful, with a resolving power 100 times that of Hubble. As TMT's preliminary design review nears, this article details how its enclosure, segmented mirror and adaptive optics will work to let astronomers peer back to the beginning of the Cosmos."
If only they had a 30 foot server... (Score:1, Funny)
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Do not despair, the article is here [canadianma...turing.com].
Thirty Meter Nano-Telescope (Score:3, Funny)
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Kowabunga dude!
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Yes, calling it the "thirty millitesla" [wikipedia.org] would avoid a lot of confusion...
Correct link (Score:4, Informative)
Correct link without the 501 error: http://www.canadianmanufacturing.com/designengineering/features/industryfocus/article.jsp?content=20090512_125904_8252 [canadianma...turing.com]
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I don't want to hear about your wardrobe malfunctions.
World's largest? Not quite... (Score:5, Informative)
"World's largest and most powerful".
Yeah, except for the 42-m E-ELT, also slated for 2018-ish. And that's still excluding radio telescopes...
42 meters? (Score:5, Funny)
Something gives me the feeling E-ELT will give us the ultimate answer about our universe.
Scratch the above... (Score:2)
...thinking about this a bit more seriously, it might actually, and...more appropriately (? ;p ), give us THE QUESTION! :>
(taking into account how especially, among others, in astronomy/astrophysics new observations and answers often lead to more profound dillemas)
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Too bad the world ends in 2012 :/
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Thirty Meter Telescope will go a long ways! (Score:2, Interesting)
This telescope design has a lot of promise.
My father is an optical designer/astronomer, and I grew up around many different designs that actually do work.
Why is a long telescope important? Well, once you eliminate the tube sag, it has certain properties.
This design almost eliminates ambient light (think of looking at the moon through fog compared to looking at the moon on a clear night in the mountains).
Because of this, even "tiny" 6-inch long-tube designs can match or exceed 24" or better telescop
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Re:Thirty Meter Telescope will go a long ways! (Score:5, Insightful)
1 'tube sag' only applies to telescopes which HAVE a long tube, that is, long focal-length refracting telescopes which have a lens at the front end, not reflectors, which have a mirror at the back end.
2 almost all large telescopes do not use any sort of 'tube' at all for supporting the optics, any solid tube would be too heavy to be useable, they use open-frame supports
3 'detail'....if by this you mean 'angular resolution' then no, a 6" telescope can NEVER beat a 24" one, the angular resolution [THETA] is determined by the equation sin THETA = 1.22 X [wavelength of light] / [telescope diameter], so a 24" scope will *always* have 4 times better (ie smaller) angular resolution than a 6" does.
4 even with this taken into consideration, large observatory-class telescopes are made large for their light-gathering capabilities, which allow them to see extremely faint objects, -not- for their angular resolution, which is limited not by the telescope design but by atmospheric seeing conditions, these fall far below the theoretical limit of a large telescope.
5. The 30m scope is not a Cassegrain, it's a Ritchey-Chretiene, same design as used in many other large and very successful observatories, and trust me, the people who build observatory-grade optics are very able to construct ANY shape of mirror they are asked to without mucking it up. Perhaps you're thinking of -amateur- telescope makers having a go at grinding a Schmidt-Cassegrain corrector plate in their garage/shed/back room using a grinding-rig they made out of broom-handles and a washing machine motor?
Your father may well be an optical designer and astronomer, you're not though.
Not trying to be nasty, it's just that nearly everything you wrote is either wrong, misleading, or half-right but mis-applied, and to the wrong thing.
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It sounds like you don't have much practical experience using telescopes either. ;)
The Rayleigh equation you state is for the theoretical *MINIMUM* resolvable angle based on aperture size but if you think that's all there is to telescope optics, you probably haven't had experience using a wide range of telescopes. I've used home-ground 10" refractors that have MUCH better resolving power than other commercial 14" scopes.
Size matters, but so do a lot of other fa
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Just a quick note even though you're an AC, a Ritchey-Chretien optical system is a Cassegrain design, so your criticism here is wrong. The TMT is actually an aplanatic variation of the RC design.
FWIW, some of the best mirrors on the consumer market are handmade, but obviously the TMT is far from being this type of mirror.
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In the spirit of a friendly discussion, I'll reply.
Common optical designs typically suffer from optical coma (where rays of light end up in unintended places). This 30-meter telescope is designed to eliminate that, however typical classical Cassegrains do suffer from this.
Secondly, there's the issue of spherical aberration, where light near the edges of the optics becomes blurred. This is preventable by design as well.
There is yet another issue of optical -quality-, which is purely dependent on the
Seeing and Rayleigh Criterion (Score:1)
'detail'....if by this you mean 'angular resolution' then no, a 6" telescope can NEVER beat a 24" one, the angular resolution [THETA] is determined by the equation sin THETA = 1.22 X [wavelength of light] / [telescope diameter], so a 24" scope will *always* have 4 times better (ie smaller) angular resolution than a 6" does.
If I look through a 6" telescope on a typical evening here in Pennsylvania, I will have a resolution of about 2 arcseconds.
If I look through a 24" telescope on a typical evening here in Pennsylvania, I will have a resolution of about 2 arcseconds.
The limiting factor is Astronomical Seeing [wikipedia.org] not the Rayleigh criterion [wikipedia.org] which you stated quite correctly.
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Because of this, even "tiny" 6-inch long-tube designs can match or exceed 24" or better telescopes in detail and quality.
I've owned a few telescopes and this statement sounds a little far fetched to me.
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Is there any theoretical upper limit on the resolving power of a reflecting telescope? For example, would a kilometer mirror necessarily be better than a 100-meter mirror? Would a 100-kilometer mirror necessarily be better than a 10-kilometer mirror?
I was imagining an army of robots spreading out across the solar system, turning asteroids into telescopes. Over centuries these robots could create hundreds of thousands of reflecting telescopes whose images could be combined to pr
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Is there any theoretical upper limit on the resolving power of a reflecting telescope? For example, would a kilometer mirror necessarily be better than a 100-meter mirror? Would a 100-kilometer mirror necessarily be better than a 10-kilometer mirror?
Telescopes have no theoretical upper limit in design, however in practice it's very different.
The wavelength of visible light is between 0.7um and 0.4um. A mirror that is made to have no less than that much surface irregularity is very difficult to make, but it can be done.
The larger a mirror is, the more surface area you have to manufacture. A single flaw or error in manufacture could render an entire mirror either useless or of inferior quality.
I'm also absolutely sure that there is a limit to ho
oh man.... (Score:3, Funny)
2018 !, I wanted to use the 30 meter telescope to fry ants in other galaxies now !, or maybe see some boobs.
R.Morton
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Hold your horses, Veruca. Daddy will get you one when we're done with this crazy tour.
http://en.wikipedia.org/wiki/Veruca_Salt#Veruca_in_the_1971_film
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Yeah, Willy Wonka rocks, have not seen that in years, I really hated that KID she was so damned spoiled reminds me of my sisters kids.
R.Morton
I've Seen It (Score:3, Funny)
"...to let astronomers peer back to the beginning of the Cosmos."
I remember that. It had music by Vangelis and a Seyfert galaxy in the forward view screen.
I'm trying to think (Score:2)
I remember that. It had music by Vangelis and a Seyfert galaxy in the forward view screen.
Thought back through my collection and checked the wiki. Drew a blank. So which movie are you thinking of?
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I bought the Cosmos DVDs to watch and caught something I missed the first time. They used a short clip of Pink Floyd's One of These Days (I'm Going to Tear You into Little Pieces) as background audio in one episode. Good ol' Puff Daddy Sagan.
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The Cosmos DVDs were remastered to include updated special effects and some previously unaired footage. They might've updated the soundtrack, but the Floyd was probably in the original.
If by 'Puff Daddy' you mean major toker, than you're correct - he used marijuana 'avidly' [druglibrary.org].
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I tried watching it recently, but between the horrible effects, dated information, bizarre analogies, odd filming locations, ridiculous "spaceship" set, and his permagrin, I just couldn't take it seriously at all. I'm sure it fit right in to contemporary 1980, but IMO it's not quite a "timeless" documentary. It was more valuable to me as a view into the late 70s/early 80s than general astronomy. Obviously that wasn't the goal of the series, which just made it all the more cringe-worthy.
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Collecting area versus resolution (Score:5, Informative)
As the actual article notes on its first page, TMT will have roughly 100 times the collecting area of Hubble: this goes as the square of the diameter of the telescope, so with TMT = 30m and Hubble = 2.5m, that's about right.
Resolving power (if the TMT can be made diffraction-limited, which it is aiming to do, but which is hard nevertheless) gets better linearly with the diameter, so TMT will have roughly 10 times the resolving power of Hubble.
The more appropriate space-based comparison in 2018 will be JWST which has a diameter of 6.5m, although JWST and ground-based ELTs are more properly thought of as being complementary, not competitive: they do different things.
But as already noted, the more appropriate comparison is with the European E-ELT which is under Phase B study now and is baselined for 42m diameter.
More interesting is where the TMT and E-ELT will be located: same hemisphere or not? Current bets are on E-ELT being in Chile, with TMT possibly going to Mauna Kea. This would be a better outcome for us astronomers than having both in the south, IMHO.
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In addition, no earthbound scope can 'see' into the UV and IR bands as the atmosphere absorbs them.
And Atmospheric Blur (Score:1)
That excludes the blur caused by the atmosphere, which Hubble does not have to worry about. TMT will have "adaptive optics" to partially compensate for atmospheric blur, but it is still a relatively new and evolving technique with certain limits. A direct comparison with Hubble depends on lots of factors and technical issues.
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Yeah, exciting stuff, but Ed Weiler himself just said at the recent Atlantis post launch news conference something to the effect that he always hears about new telescopes that will be xx times better than Hubble, but you have to take those with a huge grain of salt coming from land based telescopes. There is a lot of buzz about adaptive optics but not much substance yet and you can't see UV light from the ground.
What about that h
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Well, Ed would say that, wouldn't he? :`)
Adaptive optics is not quite the same as raw diffraction-limited imaging, no, but it's getting pretty damn good. It's a lot more than buzz: all major telescopes use it routinely.
I've been using for many years already from ground-based 8-m telescopes and it really does deliver more than HST can ... in the near-IR. Nope, it can't compete at optical wavelengths with HST ...
You're thinking Arecibo: Puerto Rico and yes, it's radio.
If ground-based telescopes are so good (Score:2)
Then why are we fixing the Hubble telescope (and developing newer space telescopes...)
Seems to me like the era of expensive/hard to maintain space telescopes is over.
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Ground based telescopes will always be worse than space based telescope due to the atmosphere.
Ground based telescopes will always have to deal with the atmosphere, and space based ones won't, yes. That's rarely the only factor in the results.
The only place ground based telescopes beat space based telescopes is ease of access.
Ah, but ease of access translates to ease of upgrades. Hubble's infrared imaging capability is about to be upgraded from 256x256 to 1024x1024... meanwhile, folks in Hawai have been at 4096x4096 for six years already, since they developed the chips for the next (James Webb) space telescope's infrared camera.
Now...a lunar base with a massive telescope...that wouldn't be all that bad.
Sure, as long as you can fabricate instruments from re
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Ah, but ease of access translates to ease of upgrades. Hubble's infrared imaging capability is about to be upgraded from 256x256 to 1024x1024... meanwhile, folks in Hawai have been at 4096x4096 for six years already, since they developed the chips for the next (James Webb) space telescope's infrared camera.
It's slightly more complicated than that. JWST's near-IR detectors were manufactured by Teledyne (formerly Rockwell), with the University of Hawai'i involved under contract for development and testing. Specs were set at the project level and the detectors have also been tested under contract by the STScI Detector Lab and, of course, by the instrument teams using them (Univ Arizona for NIRCam, GSFC/ESA for NIRSpec, GSFC/CSA for FGS/TFI).
What Hawai'i have always been very good at is giving the impression
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Good job I put that bit in about "some of my best friends are Hawai'ans", eh, Dan, now that I've seen that you're a TO for the 88 inch ... :`)
After all, it would hypocritical for me not to remember that through my Hawai'in friends (a fellow Englishman building IR instrumentation at the IfA, shall we say), I made good use of one of Klaus Hodapp's earlier "lashed-up" cameras on the 88 inch, the one with the first 256x256 NICMOS3 array in. This happened as part of the deal that was made when Hawai'i lost i
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JWST's near-IR detectors were manufactured by Teledyne (formerly Rockwell), with the University of Hawai'i involved under contract for development and testing.
What Hawai'i have always been very good at is giving the impression that they develop detectors themselves :`)
Depends on whether your definition of "develop" involves fabrication, I guess. You just said right up there that Rockwell manufactured them and UH was involved for development and testing. I think MIT Lincoln Labs was in the mix too, but at that point in time I was wrangling an SCO OpenSewer box at a trucking company, and I don't really want to go ask Don Hall even if he's in the same building, so I'll take your word for it. :)
While they're also good at getting them on the telescope quickly, it's often on small telescopes like the UH 88 inch in lashed-up dewars and (to be honest) not delivering much science.
Darn right! A slightly-smaller-than-Hubble scope that doesn't have 5-7 nights
Re:If ground-based telescopes are so good (Score:5, Informative)
As I said, ground- and space-based telescopes are actually highly complementary: it sounds greedy, but we really need both.
Space has the advantage of there being no atmosphere to block some of the incoming light and blur the image. Also, if you cool your telescope down (e.g. ESA's Herschel being launched tomorrow and NASA/ESA/CSA JWST in 2014), then you benefit from greatly reduced sky background at infrared wavelengths. This can result in an enormous increase in sensitivity in situations where the background matters, e.g. imaging of extremely faint sources.
Also, space-based telescopes can cover a wider wavelength range, including wavelengths that don't make it through the atmosphere, so some kinds of thing must be done from space (e.g. X-ray astronomy as in NASA's Chandra and ESA's XMM-Newton).
At the same time, space telescopes are much smaller than state-of-the-art ground-based ones, and thus the ground-based telescopes can catch many more photons over all. For some science (e.g. medium- to high-resolution spectroscopy of extremely faint objects where the background doesn't matter), it's all about the number of photons you can collect.
Also, if you can implement adaptive optics on your ground-based telescope, you can get higher resolution than in space.
As an example of true synergy, look at the many studies done jointly by HST and the ground-based 8-10m telescopes like the VLT, Keck, Gemini, and so on. In many cases, both were needed to complete the study.
Indeed, there are many of us helping develop both JWST and ground-based ELTs like E-ELT and TMT for exactly the same reason: we need both to get a more complete picture of what's going on out there.
Yeah, but where? (Score:2)
Reading TFA is further evidence that these so-called journalists always neglect some basic piece of information that's right in front of their nose.
- "Hey Kent, I proof-read your piece on the telescope, you forgot to indicate where in the world it's gonna be installed".
- "Sorry about that, I'll get right on it, Mr White".
So what is it, Chile? Hawaii? Canary Islands? El Segundo, California?
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They've narrowed it down to two sites. It's either going on Mauna Kea, or in Chile.
I was just talking to a guy today who works at an 8-meter-class telescope on Mauna Kea, and he was saying that right now, they have proposals for 7 times as many nights as there actually are available. He thought this might drop off a bit once the TMT is built, but I figure hey, the TMT is only one scope, so at most one of those 7 can go use it. The 8-10 meter guys are safe for probably a good while - Keck I is 17 years ol
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Heh... interesting way of looking at it.
"Sorry, Dr. Tully, but you only get 45 minutes." :)
I wonder whether they'd actually do that.
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They've narrowed it down to two sites. It's either going on Mauna Kea, or in Chile.
and
They haven't decided yet. Either Mauna Kea, Hawaii or Atacama Desert, Chile.
Thanks, guys. The article did not make it apparent, although many big astronomy projects nowadays end up at either site.
It's been a while since I've read about Arizona bagging a major project such as this, same with the Canary Islands. South Africa is sometimes floated around in these articles.
A possibility in my neck of the woods is the San Pedro Mountain Range in Baja California. To make the pitch more plausible, the local state government has begun installing low-glare street lighting in nearby urb
Slashdotted? (Score:1)