Massive Radio Telescope Starts Observing the Skies 44
New submitter cyachallenge writes with this excerpt from New Scientist: "RadioAstron, effectively the largest radio telescope ever built, is up and running. The telescope's main component, a 10-metre radio dish aboard the spacecraft Spectr-R, launched in July to an oblong orbit that extends between 10,000 and more than 300,000 kilometres from Earth. By coordinating observations with radio telescopes on Earth in a technique called interferometry, the telescope can make observations as sharp as a single dish spanning the entire distance between the two farthest dishes. When Spectr-R is at its farthest from Earth, the system acts like one enormous telescope about 30 times as wide as our planet, boasting about 10,000 times the resolution of the Hubble Space Telescope."
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And given the nature of redshifting, simply observing things near the surface of last scattering in the radio presents what would've originally been visible light images.
Re:Too bad (Score:4, Insightful)
Re:Too bad (Score:5, Informative)
Actually, in radio astronomy you can't really say it's photons. The wavelengths are centimeters to meters (a pretty large photon), and you get wave-effects everywhere.
It's not true that this or other radio telescopes are no match for Hubble. This satellite links up with ground-based telescopes and does VLBI. The baseline of VLBI -- equivalent to the aperture diameter for optical telescope -- is the distance between the linked telescopes. If you want to have a telescope as powerful as Hubble, you need to compare diameter/wavelength (Hubble example: 2.4m/440nm = 5e6). So for radio (e.g. 21 cm), you need a baseline of 1050 km. Ground-based VLBI networks, like the Australian LBA (3300km Perth-Sydney, 5500km Perth-Auckland) or the European EVN, the VLBA (8000km) reach these lengths. This brings you down to milliarcsecond resolutions, incidentally similar to the optical VLT interferometer.
RadioAstron will be on an "orbit that extends between 10,000 and more than 300,000 kilometres from Earth".
So yes, it will be a match for Hubble by a factor of 100. However, this comparison is not really helpful, as optical and radio telescopes see different things and probe different physical processes. To understand the universe, information from all wavelengths is relevant.
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You touch on something that I've been wondering about. From what I've read I understand that electromagnetic waves, such as light and radio, can also be understood as photons. And the frequency of the wave is in proportion to the energy of the photon. My question is at what frequency does one stop thinking of RF as photons. Is my little ham walkie-talkie pumping out 73cm photons when I transmit at 445MHz? Is an AM radio station pumping out a lot of football field sized photons or are photons actually j
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I think it has to do with both the photon density and the size of the thing you use to observe them. If there are few photons per cubic wavelength (even less than one), EM waves look more like photons in the sense that you need to describe them with quantum mechanics. If there are many, they look more like classical waves. Also, if the wavelength is small compared to the observer, then they are more likely to look like photons. So if you have 1 photon/cm3, and a wavelength of 1cm, it might look more lik
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Thanks for the explanation, I think I'm starting to get this now.
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The wave/particle duality is true for any and all energies, and it is wrong for anybody to try to convince you otherwise. A single photon is incredibly difficult to observe, yet even a single photon shows wave-like behavior, smearing out results. So it depends on your observation technique. A quantum optics guy told me that their rule of thumb is that anything beyond five photons is a wave.
From a theoretical standpoint however photons are absolutely necessary to describing the situation. Without it you woul
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Well if it's not photons carrying that electromagnetic energy then what is is it? You get wave effects with solid matter too... in fact you get wave effects with everything... so?
As Feynman said in one of his Auckland lectures, to the best of my recollection (so throw in some salt) - "We may talk about [it] as waves because that's convenient for certain problems but neve
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You're talking about two different kinds of waves. Matter is also a waves in the quantum mechanical sense. EM in some cases is better described by waves in the classical sense, i.e. with Maxwell's equations. Though often EM is better described as photon particles, or as photon waves that describe things like the probability of being detected at a given location.
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I was pointing out that saying you get wave effects everywhere - without describing the effects and how they are particular to photons at radio astronomy wavelengths - is kind of content free since everything exhibits wave effects.
And my main point was that in my understanding it is not true that "you can't really say it's photons. The wavelengths are centimeters to meters (a pretty large photon)", i.e., having a long wavelength doesn't make a photon not
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Our concepts of "wave" and "particle" are not terribly good fits for what photons are. Photons are photons and need to see no psychoanalysts about their identity problems ; we have problems matching the reality of photons to our concepts of "wave" and "particle", but that's our problem, not the photon's problem.
My school physics labs included a series of experiments in how sem
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Wrong! Some incredibly amazing images have come from radio telescopes such as the VLA. You can find some of those pics on the National Radio Astronomy Observatory (NRAO) Image Gallery website.
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Optical interferometry is done, so there's nothing to stop someone setting up an array of optical telescopes in which Hubble was one of the telescopes involved. Ideally, since large optical telescopes are very difficult to launch, future optical space telescopes should be designed to be used in interferometry arrays. The problem is one of synchronizing, since you can't use interference when the signals aren't in phase and relativistic time matters if they're not on a common orbit, but if you record the sig
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Optical interferometry is done, so there's nothing to stop someone setting up an array of optical telescopes in which Hubble was one of the telescopes involved. Ideally, since large optical telescopes are very difficult to launch, future optical space telescopes should be designed to be used in interferometry arrays. The problem is one of synchronizing, since you can't use interference when the signals aren't in phase and relativistic time matters if they're not on a common orbit, but if you record the signal and timestamp points along it, it should be possible to do the interference offline rather than live.
So you start to say there's nothing to stop them from doing it, and then, actually, very elegantly explain exactly what does prevent it. I would say that, at this point, our spacecraft technology would be severely taxed by multiple-vehicle interferometry. Multiple-vehicle cooperative satellite projects have been nixed for much less stringent stationkeeping requirements than an interferometer has, although there are ideas on the subject that have been discussed. Still I'd say we're a ways away from it, at
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Well, I said why live interferometry can't be done at this point. If you timestamp the data at regular intervals, a base station would be capable of stretching recorded data and doing the interferometry that way.
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Well, I said why live interferometry can't be done at this point. If you timestamp the data at regular intervals, a base station would be capable of stretching recorded data and doing the interferometry that way.
Still requires location information beyond what we currently have available on satellites, generally
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One of the more fundamental problems is that we don't have phase-sensitive detectors for visible light.
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http://www.astro.lsa.umich.edu/~monnier/Publications/ROP2003_final.pdf [umich.edu]
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You do realize that the paper basically confirms what I say? We cannot detect phase, which is why optical interferometry relies on overlaying the light directly. No signal, no timestamp. You have to keep your optics aligned to within micrometers.
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Is that a word (still) ?
Not in reference to a (highly) flattened eliptical orbit surely.
Why wouldn't it be? Oblong is a perfectly cromulent word.
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From Wiktionary:
Adjective
oblong (comparative more oblong, superlative most oblong)
Describing something that is longer than it is wide.
Roughly rectangular or ellipsoidal.
Noun
oblong (plural oblongs)
Something with an oblong shape.
A rectangle having length greater than width.
Looks like a valid description of a comet-style orbit.
Re:oblong?? (Score:4, Insightful)
I always thought Oblong was more rectangular than elliptical. Of course the rectangle with rounded corners was invented by apple.
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In before Parent is sued for billions.
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Forget "oblong", how about "massive"? Massive has to do with, well, mass. Seems that Aricebo might have the best claim for that (using the Earth itself as part of the structure).
it _will_ find extraterrestrial life (Score:5, Funny)
it's too big to fail.
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Except me. I will tell you the secret codes...for a price.
It has good resolution but... (Score:5, Informative)
.. it still "only" has 10m of aperture (+ the aperture from radio telescopes on Earth) so it will have a hard time detecting faint objects near its maximum resolution. It will be excellent at detecting small details of bright objects though.
Hats off to Russian scientists (Score:5, Insightful)
Unlike the Chinese, that seem to do a lot of "me, too" stuff (which is very impressive, of course), the Russians do work that is nicely complementing the US, European (ESA) and Japanese efforts. The Spektr-R (and RadioAstron) is something novel and unique, and will provide insights in the astrophysics and astronomy beyond the Milky Way with high angular resolution.
Another example is ill-fated Phobos Grunt. It would have been another interesting and unique experiment.
Their Website (Score:5, Informative)
http://www.asc.rssi.ru/radioastron/index.html [asc.rssi.ru]
Why such a pitifully small dish? (Score:2)
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But what is the curvature error of the TerreStar-1 dish? And of the RadioAstron? You have to compare _that_, not just dish diameter, to understand why they did not/could not make it bigger... Besides, a larger dish means more orbital interference from solar wind, etc.
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The radio telescope and the communication satellite has wildly different design goals and specs. You can't get much by just comparing the size.
Yes, but . . . (Score:2)
Diffraction (Score:2)