Can the “invisible” chromatic territory be mapped? [closed]

There are lots of "colors" (for lack of a better word) which are located outside of the spectrum visible by humans.

If a person finds a way to "record" these colors with a photographic device (full-spectrum cameras / infrared film / etc), these shades revert to a visible color once a human eye sees them.

That being said, I am wondering if the mapping of "invisible color ranges" has ever been attempted using technology (by mapping I mean cataloging, documenting).

I am assuming that even though humans cannot see the colors outside the visible spectrum, a device could be programmed to "see" or "map" them, and organize them on a chart based on their frequency.

The device could even maybe so much as explain what these colors feel like by using AI, attempt at giving them a name, or help create alternative methods for a human to see them, such as the ones brought up in this article (stereo-vision, or interlaced flickering of 2, 3, 4 colors at different frame-rates, etc). Or in turn create a database of how these colors occur in nature and what life forms are sensitive to them.

This would be an very valuable repository that could be used to study, expand or gather data about out-of-spectrum hues, with uses in science, optics, biology and art.

After looking up online, I haven't been able to find if this was attempted or not.

Is there or has there been attempts at scientifically mapping what lies outside the visible spectrum of light?

closed as unclear what you're asking by sammy gerbil, Jon Custer, ZeroTheHero, Sebastian Riese, Emilio PisantyApr 18 '18 at 16:13

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• Re, "...these shades revert to a visible color once a human eye sees them." Are you attempting to describe how existing cameras that are sensitive to invisible wavelengths are used to make pictures that humans can see? (e.g., en.wikipedia.org/wiki/Infrared_photography ) – Solomon Slow Apr 11 '18 at 21:52
• Re, "...explain what these colors feel like," and are you talking about what non-visible "colors" would look like if we really could see them? – Solomon Slow Apr 11 '18 at 21:53
• @jameslarge Yes to your question 1, I am a photographer and take infrared / uv photos often. To me they the output colors look like bright blue/yellow/red, not like something alien (obviously) - but inside a full-spectrum photo sensor/device they can be captured as they are, raw. 2-it could be many things, the second link I give in the question can be a beginning of an answer. There are many ways to describe visible colors, warm, cold, vibrant, high frequency, etc - maybe some of them also apply to non-visible ones. – MicroMachine Apr 11 '18 at 22:01
• -1 Not clear what you are asking about physics. It seems to me that you are asking about the physiological response of the eye (ie 'perception') to unusual lighting conditions using light inside the visible spectrum, not outside it. This depends on how the brain is wired. Conducting experiments to 'map' such 'impossible colours' is a physiological question. This is not physics. I think your question belongs on Biology SE. – sammy gerbil Apr 11 '18 at 22:28
• Possible duplicate of How to define the light "color" from a given spectral distribution? – sammy gerbil Apr 11 '18 at 22:36

EDIT: From the discussion in the comments, I gather that you're asking about the division of parts of the invisible spectrum into the equivalent of "colors." We have effectively done that in some sense. Different parts of the invisible spectrum have different names. The lowest-frequency ("reddest") waves are radio waves, then microwaves, then infrared rays, then visible light, then ultraviolet, then X-rays, and the highest-frequency ("bluest") waves are called gamma rays. Each of these has a name because it interacts differently with its environment (giving it a different "feel"). Gamma rays are very destructive, ripping apart atoms, while radio waves merely gently move them up and down. (There's actually a part of the electromagnetic spectrum that you can directly feel, even though you can't see it - infrared rays in a certain range of frequencies interact with the water in your body, and you feel heat as a result.)

If you want to divide the various named parts of the spectrum into finer categories, there also exist various naming schemes, and no one scheme is objectively correct. For example, UV rays can be divided into UVA, UVB, and UVC (from lowest to highest frequencies). X-rays can be "soft" or "hard" (where "hard" is higher frequency). Infrared rays can be "near-infrared" (high-frequency) or "far-infrared" (low-frequency). There's a specific category of microwaves called "millimeter-waves" which have wavelengths of about a millimeter. You could also identify "colors" in the different frequency bands based on the filters applied to various types of telescopes, as seen below. For an even more well-defined notion of color, you could consider individual atomic transitions (such as the transition of the electron in a hydrogen atom from its first excited state to its ground state), which have a well-defined frequency, and thus a very specific "color." These colors are typically named according to the characteristics of the transition that generated them (for example, the one I just referred to is called H$\alpha$, or the Lyman-alpha line). For a database of atomic transition lines, look here: https://www.nist.gov/pml/atomic-spectra-database. The original answer below is all about how you get machines (typically telescopes) to perceive these colors, and how to turn the data they perceive into a human-readable form (i.e. a color image).

END EDIT

The act of mapping the electromagnetic spectrum outside the visible range basically defines most of the field of astronomy. Astronomers use infrared, UV, radio, X-ray, gamma ray, and microwave telescopes to do exactly what you're talking about - map the sky throughout the entire invisible range. If you were to turn these telescopes onto ordinary, non-astronomical objects, they would work just as well (this is, in fact, how a lot of telescopes are calibrated).

In order to isolate a particular part of the invisible spectrum, astronomers use lenses and mirrors of different size, shape, and composition. As such, the sensitivity of a device to the invisible spectrum depends heavily on its design. For a UV or infrared telescope, the mirrors will look quite similar to the usual visible-range ones. For radio telescopes, you don't have to have the same tolerances, due to radio waves' much longer wavelength, so their "mirrors" are giant metal paraboloids. Meanwhile, for X-ray and gamma-ray telescopes, since the wavelength of the radiation is about the same size as (or smaller than) the spacing between the atoms in the mirror, reflection and focusing is very difficult, so "mirrors" are usually dense plates placed so that X-rays and gamma-rays will hit them at glancing angles. In addition, the design of the "camera" influences the telescope's response to various parts of the spectrum. For UV and infrared telescopes, a CCD is used, much like in visible-range cameras. In radio telescopes, a radio antenna (or an array of such antennae) is used. In X-ray and gamma-ray telescopes, a scintillating crystal or silicon strip array is used, which both take advantage of the fact that X-rays and gamma-rays are ionizing radiation which would destroy an ordinary CCD.

At this point, you have a device that is sensitive to a certain part of the invisible spectrum. Its output is a black-and-white image representing the intensity of the radiation coming from a particular point. In order to turn that black-and-white image into a color image, astronomers use the same thing that a normal camera CCD uses: filters. Filters further restrict the sensitivity of the device to different parts of the spectrum. They come in both broadband and narrow-band varieties. The broadband filters let in a wide swath of the telescope's sensitive range, corresponding to the "bluer" or "redder" parts of that section of the electromagnetic spectrum. So, to get a reasonably accurate mapping of the invisible spectrum to a color image, you would take three broadband filters in your telescope's sensitivity range. The one sensitive to the longest wavelengths would correspond to the color red; the one sensitive to the shortest wavelengths would correspond to the color blue; and the middle one corresponds to green. Taking black-and-white images with each of these filters, coloring them their respective colors, and layering them on top of each other allows you to map the invisible spectrum onto the visible spectrum.

The narrow-band filters are tuned to only accommodate a very narrow range of wavelengths. These wavelengths correspond to the atomic or molecular transitions of important atoms and molecules in astrophysics, such as neutral hydrogen, carbon monoxide, sodium, or oxygen. Most of the narrow-band filters are in the UV-IR range, since most atomic and molecular transitions are in that range; the only major exception that I know of is the filter that isolates the hyperfine transition in cold diffuse neutral hydrogen, which is in the microwave band with a wavelength of 21cm. Usually these filters are used to highlight specific features, such as the star-forming regions of a galaxy or nebula. When narrow-band filters are used, the colors are assigned somewhat arbitrarily, since they don't correspond in any real sense to the broadband RGB filters in our eyes and in cameras. Many of the most striking astronomical images you'll see are composites of three narrow-band filters.

In summary: it is possible to make a color image of the invisible spectrum by using a device that is sensitive to that spectrum and making a composite of three filters applied to that device.

• @sammygerbil I covered both senses, I think. Astronomers catalogue (i.e. map, as in scientifically discover unexplored territory in) the night sky across the visible and invisible spectrum, creating compilations of images like the Sloan Digital Sky Survey. These catalogues are compiled using specific telescopes using specific filters, which can be composited together to form color images, mathematically mapping part of the EM spectrum onto the visible spectrum. – probably_someone Apr 11 '18 at 23:00
• @sammygerbil But they are exploring and mapping the EM spectrum. For example, high-energy gamma-ray astronomy, in its efforts to find the highest-energy EM radiation that exists, is a direct effort to explore and map the upper end of the EM spectrum. We have no real idea where this high-energy gamma radiation actually comes from, so we aren't really studying the objects that emit this radiation in any meaningful way. In this specific effort, we are purely trying to find the "end" of the spectrum, which sounds an awful lot like mapping the EM spectrum itself. – probably_someone Apr 11 '18 at 23:18
• @sammygerbil I agree that the visual representation of invisible radiation is arbitrary. This is why I mentioned that exact point in my answer. The OP wanted to know about "attempts at scientifically mapping what lies outside the visible spectrum of light," and I gave him that information, while also saying that the mapping between a telescope's output and a color image is arbitrary. – probably_someone Apr 11 '18 at 23:20
• @sammygerbil First of all, who are you to say what an astronomer is and isn't allowed to be interested in? I know of several astronomers who would be happy to contradict you on that point (the fact that the "end" of the EM spectrum is even being studied is proof of their existence). I don't see where you draw the line between the nature of the EM spectrum and cosmology; since studies of cosmology depend heavily on the nature of the EM spectrum (e.g. the polarization of the CMB), you can't say the significance of this is "entirely cosmological." – probably_someone Apr 11 '18 at 23:46
• @sammygerbil Also, where do you see the OP asking, "what 'colours' lie outside those which are visible?" The question I see up there is, "Is there or has there been attempts at scientifically mapping what lies outside the visible spectrum of light?" This can be interpreted in two ways: either "Have efforts been made to determine what kind of radiation can exist in the universe?" to which the answer is yes, from high-energy gamma-ray astronomy, or "Have efforts been made to map the kinds of objects that cannot be seen with visible light?" to which the answer is also yes. – probably_someone Apr 11 '18 at 23:47