Gigantic Chinese Telescope Opens To Astronomers Worldwide (nature.com) 28
The world's largest single-dish radio observatory is preparing to open to astronomers around the world, ushering in an era of exquisitely sensitive observations that could help in the hunt for gravitational waves and probe the mysterious fleeting blasts of radiation known as fast radio bursts. From a report: The Five-hundred-meter Aperture Spherical Radio Telescope (FAST) in southern China has just passed a series of technical and performance assessments, and the Chinese government is expected to give the observatory the final green light to begin full operations at a review meeting scheduled for next month. "We do not see any roadblocks for the remaining transition," says Di Li, the chief scientist of FAST. "I feel both excited and relieved." The complex project has not been without challenges â" it has a radical design and initially struggled to attract staff, in part because of its remote location. But the pay-off for science will be immense. FAST will collect radio waves from an area twice the size of the next-largest single-dish telescope, the Arecibo Observatory in Puerto Rico.
The Chinese observatory's massive size means that it can detect extremely faint radio-wave whispers from an array of sources across the Universe, such as the spinning cores of dead stars, known as pulsars, and hydrogen in distant galaxies. It will also explore a frontier in radioastronomy -- using radio waves to locate exoplanets, which may harbour extraterrestrial life. Since testing began in 2016, only Chinese scientists have been able to lead projects studying the telescope's preliminary data. But now, observation time will be accessible to researchers from around the world, says Zhiqiang Shen, director of the Shanghai Astronomical Observatory and co-chair of the Chinese Academy of Sciences' FAST supervisory committee. From two years ago, China Built the World's Largest Telescope, But Has No One To Run It.
The Chinese observatory's massive size means that it can detect extremely faint radio-wave whispers from an array of sources across the Universe, such as the spinning cores of dead stars, known as pulsars, and hydrogen in distant galaxies. It will also explore a frontier in radioastronomy -- using radio waves to locate exoplanets, which may harbour extraterrestrial life. Since testing began in 2016, only Chinese scientists have been able to lead projects studying the telescope's preliminary data. But now, observation time will be accessible to researchers from around the world, says Zhiqiang Shen, director of the Shanghai Astronomical Observatory and co-chair of the Chinese Academy of Sciences' FAST supervisory committee. From two years ago, China Built the World's Largest Telescope, But Has No One To Run It.
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I used to get mad about the whole "its it's" thing, and make a comment such as yours. But I've learned as I've gotten older to simply relax.
I am 100% sure what is the correct usage.
However, via muscle memory, fast typing, whatever, I make the mistake sometimes. Seems to be random. I have done it with Their, They're, and There, even though, again, I am 100% sure what is correct. There are several other examples like this that I've noticed in the past.
I recommend cutting the guy some slack.
PS: when it is
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That's funny,I thought the same about the USA, and Russia, and Japan, and Europe
No, not the USA. While China is moving forward, America is stepping back.
The Thirty Meter Telescope is on indefinite hold due to objections by a small vocal minority and spineless politicians.
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Yeah, it's faintly ridiculous watching our rivals beat us scientifically while making fun of them... that's the sort of behavior mormally found in schoolyard bullies.
Anyone? I am appalled that we don't even have a pro-nuclear candidate--not a one of our presidential hopefuls actually gives more than a token nod to science.
Posted under my name because, what the hell. Cue the flame war and troll mods.
Can They Pair This With Arecibo? (Score:2)
for even better resolution?
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Probably not since they are on pretty much opposite sides of the Earth and can't see the same thing at the same time.
Re:Can They Pair This With Arecibo? (Score:5, Informative)
Arecibo can be "pointed" approximately +/- 20 degrees via this method. The Chinese scope has motors behind each of the aluminum panels so they can "re-shape" the dish to change its aiming point. But its maximum offset is +/- 26 degrees when using a 300 m aperture, +/- 60 degrees when using a 200 m aperture. Since they're on almost opposite sides of the Earth (140 degrees separation in longitude), you'd need to point both within 20 degrees of the horizon (70 degrees from zenith) to combine them into an interferometer [wikipedia.org]. Not gonna happen. (And no you can't wait for the same section of sky to rotate overhead at the different locations. Interferometry relies on simultaneous reception of EM waves at all locations. That's why it's old hat in radio astronomy, but has only been used in optical astronomy for a couple decades. You need to align the signal received by the different telescopes to within a fraction of the wavelength of the EM wave you're observing. This is relatively easy with radio wavelengths, damned near impossible with optical wavelengths.)
However, the point of interferometry is to provide angular resolution. When you combine two telescopes at opposite ends of the Earth into an interferometer (radio astronomy folks prefer to call it aperture synthesis [wikipedia.org]) you're basically making a telescope dish as big as the Earth, then covering up all of the dish except for two points at opposite edges. The result is a single telescope which has the angular resolution of a dish as large as the Earth (that's how they were able to image that black hole despite it being 55 million light years away), but with the sensitivity of only the two telescopes you're combining. So you don't need a large dish like this or Arecibo to create an interferometer. The smaller dishes mounted on mechanisms which allow them to tilt and rotate are good enough. In fact they're better because the more such dishes you have, the less noise and more uniformity there is in your signal and imagery. Using only two telescopes in an interferometer creates high resolution in one axis, crappy resolution in the other.
The large surface area is only needed if you're trying to study extremely faint radio sources. In that respect, Arecibo is at 18 degrees North latitude, while FAST is at 27 degrees North latitude. So they can both observe much of the same area of sky as it rotates over them through the course of a day, and will complement each other. Also note that Arecibo is technically still bigger. Arecibo is a 305 m spherical dish - an artifact of it being constructed using Imperial units - 1000 ft in diameter). FAST is arranged spherically, but the individual panels are reconfigured into a parabola depending on where you wish to observe (which eliminates the aberrations). The entire dish can't be reconfigured this way; only 300 m of it at a time. What the larger 500 meter diameter does is give more angular range than Arecibo, allowing observation of parts of the sky which can't be "seen" by Arecibo.
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I think the entire Arecibo dish can't be used at once, the effective size is more like 200M. No sure though. (it may vary with elevation)
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265m iirc. So only 35m less than FAST's usable aperture I guess.
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When comparing Arecibo to FAST it should also be noted that Arecibo can receive and transmit signals up to 10 Ghz, but FAST can only go up to 3 Ghz, a serious limitation for SETI/METI projects as well as for any interstellar or deep space communication of our own. Maybe the Chinese can upgrade their dish at some point in the future to receive shorter wavelengths though. Not sure if the design allows for this.
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Upgrading the telescope to observe at higher frequencies (shorter wavelengths) requires two main things. First, a different electronics package at the focus of the dish, which is relatively easy. Second, the dish surface needs to be made more precise. The usual design rule is that the dish surface needs to be a parabola to a precision of 1/20th of the wavelength; for 10GHz (30mm) this means they need a precision of ~1.5mm. Rebuilding an entire 500m aperture to achieve this precision is a really big job.
why one big one? (Score:2)
Honestly, I don't get the value of this tool. Sure bigger is always cooler, and that might be reason enough to do it, but it seems like they could have gotten more out of building dozens of much smaller connected radio telescopes that could have an effective aperture much larger than 500 meters. Of course by synchronizing hundreds of telescopes around the world we were able to image a black hole. So the technology is highly capable. This fixed telescope won't be able to help in projects like that very well.
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It's all under one government?
That's my guess
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"This fixed telescope won't be able to help in projects like that very well."
It ain't fixed, that kinda the point. I know you can't possibly RTFA or read TFWikipedia but trust me, it ain't.
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Honestly, I don't get the value of this tool. Sure bigger is always cooler, and that might be reason enough to do it, but it seems like they could have gotten more out of building dozens of much smaller connected radio telescopes that could have an effective aperture much larger than 500 meters. Of course by synchronizing hundreds of telescopes around the world we were able to image a black hole. So the technology is highly capable. This fixed telescope won't be able to help in projects like that very well.
Why is one big telescope a good choice?
You are correct, it simply isn't a good choice. There is a reason why the only other antenna I can think of like this is very old. The data may be interesting, but due to the lack of complete redundancy in the antenna system any extremely weak observations will always be difficult (if not impossible) to confirm. There are other limitations as well that you wouldn't have with an array of smaller dishes. It seems to me that this is more about prestige than science, but that could be a contributing factor in t
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An array of smaller apertures configured as an interferometer can get you the same angular resolution as a single larger aperture. The angular resolution is determined by the effective width of the interferometer, i.e. the distance along its longest axis. However, the lowest signal strength the system can receive is determined by the collecting area. If you want to get a very weak signal above quantum noise in your receiver, you need a large collecting area. This dish will be able to receive weaker sign
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Many smaller apertures still contribute to the total aperture size so the question is why build one large telescope when many smaller ones with the same total aperture size could be used instead for the same sensitivity and better angular resolution? Is one large telescope more economical?
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You are correct, it simply isn't a good choice.
He never said that and your assumption is wrong. Interferometers are good at some things and not so good at others. They are not a replacement for one large aperture. If you want to receive a distant or weak signal for something like SETI for instance you want one large dish. For transmission of signals you normally want one large dish as well, but I have also read plans for using interferometry to transmit high power signals for METI but I think that was not because it was just as good as one large dish bu
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Interferometry, which uses multiple telescopes separated by some distance, gives you the resolution you'd get from a monolithic telescope with an aperture similar to that distance. It does not give you the sensitivity though. Sensitivity depends more or less on collection area.
If you want to see small, bright things, you can use an interferometer, although your ability to generate an image will depend on how many individual elements you have, how they're arranged, and whether you can move them or not. If yo
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1. One big telescope gets you more total surface area, and hence sensitivity, than spending the same amount of money on lots of little ones. (At least, if you can build the big telescope into an appropriately-shaped valley, like this one.)
2. Lots of little telescopes require a lot of computing hardware to run them: you need to handle dozens of streams at a few GB/s each, rather than just one, and they require more intensive processing.
A single big telescope like this has two downsides. First, its resoluti
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There is some cost optimum. More small dishes means more receiver systems and data processing that scales something like the square oft the number of dishes. The cost of the processing is substantial, large radio telescopes use the latest 100G networks and many racks of GPUs for signal processing.
Its possible that a very large fixed dish makes sense.