It's a fairly simple question (at least in my layman's mind). Can a radio telescope that has no mirrors or lenses to capture visible light (to human eyes) still produce imagery like an optical telescope such as the Hubble? I'm talking just ROYGBIV light (no infrared or UV).
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$\begingroup$ Could you clarify whether you mean (a) using radio telescopes to collect and process visible light, or (b) generating imagery from the collected and processed radio wavelength light that is visible to us humans (who cannot see radio waves)? $\endgroup$– David HammenApr 25, 2017 at 19:19
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$\begingroup$ @DavidHammen - I suppose both. But more like (b). Assuming the Hubble renders an image that would look exactly as if I was there looking at the object through a spaceship window, can a radio telescope (say space-based) spit out an accurate replica of that image? $\endgroup$– iMerchantApr 25, 2017 at 19:41
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$\begingroup$ You should to edit your question to clarify what you are asking. I suggest leaving out having a radio telescope capture visible light because that apparently is not what you are asking. The correct answer will inevitably involve arrays of radio telescope antennae, long baseline interferometry, aperture synthesis, and possibly timing (in the case of "imaging" an asteroid). I might have time later this evening to update my answer one more time now that I've got a partial idea what you are asking. $\endgroup$– David HammenApr 25, 2017 at 20:04
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3 Answers
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Can a radio telescope that has no mirrors or lenses to capture visible light (to human eyes) still produce imagery like an optical telescope such as the Hubble?
Of course, either via false color or pseudocolor. A false color radio image maps various frequencies (typically three) in a multispectral radio image to visible colors. A pseudocolor radio image maps various intensities in a single spectrum gray scale radio image to visible colors. The same techniques are also used for gamma, X-ray, UV, IR, and microwave imagery. We can't see in those frequencies, so something needs to be done to the captured imagery to make them visible to us.
If the question is asking whether a radio telescope can be used to capture visible light, the answer is no. I'll start with the receiver. It's designed to capture long wavelength radiation. Photons in the visible spectrum will have minimal, if any, impact on a radio telescope receiver.
An even bigger problem with some radio telescopes is depicted below.
Source: https://en.wikipedia.org/wiki/Haystack_Observatory
The above is the Haystack Radio Telescope at the Haystack Observatory in Westford, Massachusetts. The radome protects the telescope against weather, but also hides the antenna from optical light. A couple of other radio telescopes at the Haystack Observatory show yet another problem:
Source: https://en.wikipedia.org/wiki/Haystack_Observatory
The fixed zenith telescope antenna in the foreground and the fully movable telescope antenna in the background are made of a wire mesh, making them see-thru in the visible portion of the spectrum. This wire mesh construction is quite common for long wavelength radio antennae because it allows the wind to blow through it. Shorter wavelength radio antennae are more likely to be solid, but those are oftentimes painted.
A wire mesh with wires separated by centimeters is very smooth to a meter long radio wave, as solid surface smooth at the millimeter level to a centimeter long radio wave. A surface with millimeter-scale roughness would make for an extremely lousy optical mirror. There is no reason to make a radio telescope antenna smooth to the visible portion of the spectrum, and there are many millions of reasons (i.e., many millions of dollars) not to do so.
answered Apr 25, 2017 at 10:10
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$\begingroup$ @CarlWitthoft -- My initial take on the question was the same as comprehensible's. After all, radio astronomy imagery is often seen in print. I added to my answer in case the question is whether radio telescopes can be used to gather visible light. I'm going to ask the OP to clarify the question. $\endgroup$ Apr 25, 2017 at 19:17
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Here are images produced with radio waves in RGB, but they are frequency-inaccurate. YES, Radio telescopes can produce imagery... NO, radios are not in the visible range, otherwise a talky walky areal would glow like a lamp when it transmits information. No, Radio antenna don't capture photons electrically and it is their voltage change which is measured, they can only get hot and malfunction from light.
The question is mystifying... You must read about electromagnetic spectrum energy!!! it's simple!! it is the source of all collected astronomy data and studies. It's like subtraction and division in maths, electromagnetic spectrum is fundamental. If you mix up photons and radio waves, it's like you are mixing subtractions and divisions.
The bubbles here are supernova remnants, on the right is a radio galaxy.
The colors here are red to green based on real radio wave length according to the researcher, however i think it's a compilation of multiple images of different radio periods. source is 70-230mhz = 1.2meters to 4meters
https://www.ted.com/talks/natasha_hurley_walker_how_radio_telescopes_show_us_unseen_galaxies
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$\begingroup$ What does this mean: "_ waves of the electromagnetic-light spectrum which are >15cm, of which photons have roughly 500nanometer wavelength_". Radio telescopes observe light far outside the visible spectrum, and only produce false-color images. $\endgroup$– pelaApr 25, 2017 at 9:39
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$\begingroup$ I added that after reading the question again, because the phrasing implies that a radio antenna can infer data about ROYGBIV photons, and I felt that my answer should state that radio and light astronomy require previous understanding of the electromagnetic spectrum, which is the energy palette/ the basis for all known astronomy data. the simpler answer is NO, radio antenna can't capture ROYGBIV light imagery, but they can captre imagery same as hubble, so they can capture imagery, which we see in rgb. $\endgroup$ Apr 25, 2017 at 9:54
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1$\begingroup$ This doesn't answer the question (which admittedly is very naive) $\endgroup$ Apr 25, 2017 at 13:55
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$\begingroup$ Agree with @CarlWitthoft. I don't think it makes sense to say that radio telescopes capture the same image as optical telescopes, even though it's the same object, at least not in the sense that the OP seems to ask for. You are looking at different physical processes responsible for emitting the light. $\endgroup$– pelaApr 25, 2017 at 14:53
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$\begingroup$ explicitly, there were two questions: can radio telescopes produce imagery, to which the answer is yes. that's the question i answered, because radio telescopes are used to produce imagery. The second statement of the question was unclear, so i explained that too... radio energy does not produce photons or visible range data directly. $\endgroup$ Apr 25, 2017 at 16:09
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The answer is either "no, of course not," or "yes, in a pathological sense." A radio "telescope" captures photons which are capable of forcing electromagnetic responses in metal -- which is to say, the induced voltage caused by an E-M field. The statistical odds of a visible-range photon causing an induced signal of detectable level in a metal antenna are ridiculuously small.
answered Apr 25, 2017 at 13:57
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$\begingroup$ A radio antenna returns a voltage which has a signal to noise ratio. the noise is the baseline under which the signal is a faint random noise. if a radio antenna recieved 100000 times more light than a mid day sun, it would not produce any useable data as regards direction or photon colors. the antenna would change temperature only. $\endgroup$ Apr 25, 2017 at 16:20
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