Slashdot Mirror
Engineering the 30-Meter Telescope
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."
Correct link without the 501 error: http://www.canadianmanufacturing.com/designengineering/features/industryfocus/article.jsp?content=20090512_125904_8252
Do not despair, the article is here.
"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...
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.
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.
The Cosmos TV series by Carl Sagan. I loved that show.
Tiller's Rule: Never use a word in written form that you've only heard and never read. You will end up looking foolish.
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 factors that ultimately determine a scope's actual resolving power.