I'm still not sure if I understand what your saying right. "It's analogous to looking at an x-ray or image of any other spectral region that is beyond our unassisted vision, either because of wavelength or intensity threshold." Our ability to see an object does not dictate what wavelength of the electromagnetic spectrum it gives off. Regardless of how dim it is to our eye. Just because we are not able to see it that way, doesn't mean it is not that way. Each gas will always absorb and emit a very specific wavelength of the electromagnetic spectrum. I understand that our eyes are very very limited in seeing what is actually there, and that each object would never look like what it does in a photo to the naked eye, but that is just to the naked eye, the elements giving off those wavelengths are still actually there, and actually those wavelengths. Digital cameras are calibrated to reproduce the same section of the electromagnetic spectrum that our eye sees, the same way the eye sees it. They are not picking up other parts of the invisible (to us) spectrum and assigning colors to them. This is how they measure the composition of the universe, galaxies, stars ect. I don't think imaging visible light, and representing the X-ray part of the spectrum are the same thing. Visible light will actually emit the photons that our eyes can see, when you image a galaxy, or nebula, your simply collecting more of the light we *can* see. We have to do a false color map outside of visible light, to represent those other energy levels. If our eyes could collect photons without updating at 30Hz, we would be seeing much like what the photographs are. "Galaxies do not look like their photos, in real-time, naked-eye views, regardless of viewing distance. Ever. The images are always representational and more analagous to art (or even a sort of intensity map of flux levels) than a "xerox copy" or a daylight snapshot of an everyday scene." I think galaxies would look very like their photos if our eyes were more sensitive to them. Again, the photographs are calibrated to pick up the same section of the spectrum that our eyes do. They are not creating any new colors, they are just gathering more photons over a longer period of time. "There is no doubt that she would see galaxies as being tinted differently than we do." I understand that the perception of the electromagnetic spectrum is all about calibration, but the point is this, the average of all deviations of how each eye picks up light will still fall in a mean of visible light, and for the most part humans eyes are calibrated to see the section starting at the end of UV as violet, and and the beginning of IR as Red, based on those wavelengths. This is a direct function of the temperature of our star. If we lived on a planet closer to a cooler star, our eyes would have evolved to see light in the IR section of the electromagnetic spectrum as cooler stars give off much more light in this range. So, what I'm saying is that because our digital cameras are carefully calibrated to pick up visible light the same way our eyes do, if our eyes were are effective as cameras at capturing those photons, the galaxies to our eye's, would look like the photographs. The photographs are directly engineered after how our eyes pick up and perceive light. This is why they use Red, Green, and Blue pixels to pick up light in a digital camera even tho these are not the primary colors, because the receptors in our eyes pick up Red, Green, and Blue light. They also design the sensor with almost twice as many green pixels than red and blue, because the human eye is *most* sensitive to green light. I will admit there is some deviation to all of this, but my argument is for the most part, *if* our eyes were sensitive enough to see a galaxy like a camera does, it would look very very similar. This is fun fruit for thought. Should keep this one going. Chuck Hards wrote:
You guys mentioned that the colors are there- but you missed my point- that we need instruments to perceive them. To the naked eye, the objects are not bright, are not color saturated. Even if we were close to them, they would appear dim, and the colors would be fleeting, at best. This is well-known and not really debatable.
Colors represent energy levels, and that is the way we perceive the differences in those energy levels. For deep-sky astronomical objects, we generally need large aperture or time exposures to bring the flux level up to the point where we can percieve the colors and see the dim, outer regions of deep-space objects.
It's analagous to looking at an x-ray or image of any other spectral region that is beyond our unassisted vision, either because of wavelength or intensity threshold.
Galaxies do not look like their photos, in real-time, naked-eye views, regardless of viewing distance. Ever. The images are always representational and more analagous to art (or even a sort of intensity map of flux levels) than a "xerox copy" or a daylight snapshot of an everyday scene.
Joe mentioned that some people may perceive tints differently and this has also been documented. We've discussed in this forum before how some humans have additional color receptors in their eyes that allow them to see colors completely hidden from most of us. One English woman with the condition would laugh at her friends who thought they were wearing color-coordinated outfits, but to her eyes, they clearly were not! It took her many years before her wondrous ability was recognized- she sees with a richer color pallete than most of us. There is no doubt that she would see galaxies as being tinted differently than we do.
So, I maintain a "yes and no" attitude on what is "correct" color in deep-sky objects. Certainly a lot of what we think of as correct is based on learned behavior. What we are used to seeing, what NASA and NOAO has spoon-fed us over the decades. There is an established paradigm for these objects and we frame our judgements based on that model. Is it correct in an absolute sense? No, for the reasons outlined above. Is it correct statistically? Is there a portion of the bell curve of color processing that we can assign as having more validity than the extremes? That answer is a *qualified *Yes. _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.slas.us/gallery2/main.php Visit the Wiki: http://www.utahastronomy.com