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| Well, that's how we learned it in school: the spectrum of white light is composed of the colors Red, Orange, Yellow, Green, Blue, Indigo, and Violet. To be honest, there is no violet in the spectrum. Violet is a darker version of the color Magenta (deep purplish red). And Magenta is only seen when there's the "overlap" of the first supernumerary arc's red with the ultramarine blue colored concave inner fringe of the Primary Rainbow. I think Sir Isaac Newton observed the first supernumerary arc but didn't knew about the existence of these "extra" arcs at the concave part of the Primary Rainbow. And thus... are today's youngsters at school still learning about the impossible color in the spectrum: "Violet" (should be Ultramarine Blue). |
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| Violet is a spectral colour. I.e. single wavelength. |
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Danny Caes: I appreciate your research, but how is this knowledge useful for astrophotographers? |
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| Good question. It (Newton's "violet") is something I noticed on illustrations of the spectrum (in schoolbooks, etc...). These illustrations show some sort of deep pink at the blue end of the spectrum: the so-called "violet". As far as I know, the spectrum of white light, projected by a prism, doesn't show this pink at all, it's just the deep Ultramarine Blue (more or less the same as Indigo Blue). J.W.Goethe (Johann Wolfgang von Goethe) was aware of Newton's rather schoolish approach of the spectrum. See Goethe's Farbenlehre. See also James Clerk Maxwell's spectrum, composed of just the three basic colors Red-Green-Blue (Ultramarine Blue). And it's true, because when the spectrum of the sun's light is projected by an equilateral prism (three angles of 60°), at, say, ten meters or more, then the three basic colors R-G-B stay visible, while the "overlapping" colors Yellow (between the Red and Green) and Cyan blue (between the Green and Blue) disappear. And that's what Goethe noticed. The color Violet (Magenta) only becomes visible when two spectra are projected, creating the overlap of the Ultramarine Blue of the first spectrum with the Red of the second spectrum, and thus it is also seen in the Primary Rainbow when the Supernumerary arcs are also present (a repetitive series of spectra). And... the answer to your question: this knowledge is not useful for astrophotographers, but... it could start another look at Isaac Newton's rather simple (read: schoolish) interpretation of the spectrum. I think one should learn about Maxwell's spectrum (R-G-B) and also about the "other" three basic colors Y-C-M (Yellow-Cyan-Magenta), and how those six colors appear in Goethe's color-circle. |
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Interesting write up, Danny. Should be investigating further. However, if I recall right, back in the school approach the primary colours were red, yellow and blue, or am I wrong? Ciao Lorenzo |
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Yes and no. The colors Red, Yellow, and Blue are the painter's colors. That's how artists learn about the three basic colors. They have also the so-called Color Wheel, on which these three basic colors are printed, with also the "in between" or "overlapping" colors Orange, Green, and Purple. However, offset printers know the three basic colors Cyan, Magenta, and Yellow, which show much more, say, reliable colors. With these three basic colors (C-M-Y) all other colors could be created. Interesting to know that offset printers need the extra fourth color Black to give their printed illustrations (photographs / paintings / drawings) much more depth (all possible photographed or painted black objects, such as the starry sky, should really look black, and not some sort of dirty dark green, because that's how it looks when only the three colors C-M-Y are used, as ink). See also: WIKIPEDIA - CMYK color model. |
