China Building World's Biggest Radio Telescope

Zothecula writes "Since its completion in 1963, the Arecibo Observatory in Puerto Rico, with a diameter of 305 m (1,000 ft) and a collecting area of 73,000 square meters (790,000 sq ft), has been the largest single-aperture radio telescope ever constructed. But Arecibo is set to lose its title with construction now underway in Guizhou Province in southern China of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Upon its expected completion in 2016, FAST will be able to see more than three times further into space and survey the skies ten times faster than Arecibo."

Comments

It's been awhile since astro classes, but...

[Colonel Korn]

Given the 5 to 3 ratio in apertures between the two telescopes, I think that it will be able to "peer" (25/9)^0.5 = 5/3 = 1.67 times "further into space," where "peer" means resolve an object at a given signal to noise ratio. Collected light scales with the square of aperture, but signal to noise ratio only improves with the square root of the number of collected photons. In more useful terms, it should be able to resolve the same thing to the same statistical certainty in 3/5 of the time.

Re:It's been awhile since astro classes, but...

[asvravi]

Photons? For a RADIO telescope?? Yes, quite a while since your astro classes.

The SNR you quote, which improves as square root of the collected radiation (radio waves), is voltage SNR. In terms of power, you still get a 9dB SNR improvement for 3 times the collected radio waves, and in these electronics, it is electric power which is the ultimately used. However, the improvement factor should again be raised to power 1/3 to get distance, since the amount of signal power collected by an aperture, after spherical dispersion from a star, drops as the third power of the star's distance. So.. (25/9)^(1/3) = 1.4 times.

Consequences

[JoshuaZ]

More radio telescopes are generally a good thing. One of the major tensions in the field now is whether one should have large radio telescopes or lots of comparatively smaller ones that coordinate their work. Both methods have different advantages. Lots of smaller telescopes linked has the major advantage that if some of them go down for some reason one can still do good science. However, the larger ones can have lots of neat technologies. As TFA discusses, this telescope (FAST) will be able to deform its mirrors in real time to focus on sources. That will help a lot for work on faint radio sources.

However, I'm not sure that this is the best use of resources. As discussed in TFA, the Square Kilometre array is being built by a variety of countries working together, and it will do a lot of the same stuff. http://en.wikipedia.org/wiki/Square_Kilometre_Array However, the SKA and FAST will be looking at different regions of the sky, and where they do overlap will be looking at different times. So overall this is helpful. Personally, if I were going to be putting this much resources into interesting Earth-based astronomy, I'd probably want to focus more on increasing our neutrino detectors. We're not investing very much in that, and it is a very new, very interesting field of astronomy/astrophysics. Moreover, neutrino astronomy is pretty much the only thing that can give us warning (albeit only a few hours) if a nasty supernova happens in our vicinity. Right now, that doesn't look likely, but it would be nice to have some warning in case our models are off. Moreover, even without a threat issue, since neutrinos can arrive before the light from a supernova (since the neutrino burst occurs before most of what we would call a supernova, and neutrinos travel at very close to the speed of light), they can help us point our optical and X-ray telescopes in the right regions before we the light reaches us, which is really helpful for advancing our understanding of such events.

Overall though, shouldn't be complaining. It is very difficult to get almost any good funding now for astronomy and cosmology research. In that regard, this is a good thing.

Re:Consequences

[jd]

Overlap is actually a good thing, since observations that can only be repeated on the same instrument or same class of instrument cannot be definitely attributed to a cosmological source - it could be explained equally well as a flaw in the design of the instrument. Having two entire classes of radio observatory being able to validate each other will permit testing and validating of the devices.

Re:SETI

[SETIGuy]

Not sure if I'm supposed to mention it, but a couple members of the SETI@home team visited the site about a month ago.

Re:Going to be tricky to censor the aliens

[the gnat]

Why are you trying so desperately to turn any discussion about China into a political one?

Well, why not? Every discussion about the US turns into a long list of complaints about how either a) America sucks and has always sucked, or b) America is giving up its superpower status to the Chinese.

Re:'Build it Bigger' indeed

[jd]

I dunno. The politics over SKA, where it would be located, etc, show that people do indeed care. Nobody can put a telescope even the size of the Lovell dish into space, never mind the size of this monster. Single dishes have benefits (such as reduced edge effects) that arrays do not, which is extremely important for some of the science needed. Radio telescopes are still the only systems you can build large interferometers from (you can do small optical interferometers, but that's it). RFI is an increasing problem for radio observatories, due to flagrant abuse of the spectrum by many nations, and it's much easier to shield one site than a hundred. Precision-engineering a single dish of this size will require advances in material science that will have spin-off benefits in other fields.

In short, there's lots of reasons for them to do this and no obvious reason for them to copy SKA or SHA.