Donn

Cap'n - can you point me to a source of information about this colour removal question. For e.g. To remove blue seems to mean *only* blue, thus leaving green (as next in the spectrum) - so what does light minus blue look like? you said: But that seems strange to me, the other colours don't 'have blue in them' they are pure wavelengths unrelated to blue. You see my problem? Accurate answers to simple little questions about light and colours?

I have his reply, if you want to read it. He still votes for a blue sky on Mars and I cannot argue with him becuase I do not know enough. One of his statements is that if blue is removed from the spectrum the resulting colour is yellow NOT red; which could be perfectly true; I just do not know! ______________________________________ Hi Donn, Thanks for your response. I found it interesting. It seems you have put considerable effort into all this. The links below affirm the fact that the colour of the Martian sky can be non-other than blue. It appears that NASA have NOT, from the evidence at hand (essentially 'proven' by Keith Laney's processing - see below), been 'changing' the colours; but they most certainly HAVE been mis-representing the colours pictures to the public by incorrectly combining the colour channels from the Pancam sources. Of course, I agree with you that the Martian sky, like that our planet, can change depending on conditions; however, the Martian sky is generally a rather light blue (as could be expected, due to it's thin atmosphere) as is proven by the (truly) True Colour pictures composed by Keith Laney, the NASA/Ames image processor, as taken from NASA's own original data (no, it has not been modified by Keith): http://www.keithlaney.com/spirit_color_images.htm Here Keith explains the process, very clearly as far as I'm concerned, of obtaining True Colour images from the raw NASA feed: http://www.keithlaney.com/spirit_color_images_calibration.htm His processing of the colours in the correct way makes complete sense to me and I don't know why I didn't think of this in the first place (maybe because I'm not a space image processor *LOL*). The reason the sky looks blue', and these are NASA's own words: "The visible violet light has a wavelength of about 400 nm. Within the visible wavelength spectrum, violet and blue wavelengths are scattered more efficiently than other wavelengths. The sky looks blue, not violet, because our eyes are more sensitive to blue light (the sun also emits more energy as blue light than as violet)." (Hence this should apply to ANY planet with an atmosphere, such is the case with Mars.) See: http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html I really don't wish to see this kind of thing turn into an argument and perhaps it would be a good idea for us to sit down and discuss it sometime. To keep things objective, I have to point out one or two erroneous conclusions you have put forward in your response document: 'Point 2' "The dust, some of the particles being large enough, reflects the other colours and because the blue (And others? Unsure.) has/have been subtracted this causes a general scattering of red - such that wherever you look there is a supply of red light. I emphasize this because the red light is not "effectively removed" at all; no more so than blue light is removed from Earth's sky by Raleigh scattering." Specifically, I am referring to the statements, "These have a special effect on the higher-frequency wavelengths, they absorb blue light.", and (this),"causes a general scattering of red". -This is simply NOT the case: An absorption of Blue would cause a reflection (and some scattering) of Yellow, NOT Red- Also, I do not see how you can say that it is a fundamental mistake to say that, "The secondary effect of the dust particles would be one of scattering the incoming light, and thus causing objects on the ground to appear turquoise (or 'bluish') by effectively removing the red component from the direct light." I would certainly say that my wording here is perhaps NOT 100% accurate, and for that I apologise, since I do NOT intend to imply that ALL of the 'red component' from the direct light is removed. I would say, however, that a large percentage would potentially be removed, depending on the degree of scattering, in the case of having a 'red-scattering' Martian atmosphere. I certainly do NOT mean to imply that the Red light which would be scattered in this case will NOT reach the surface; it will, however, reach it in diffuse form (the degree of which would depend on a number of factors). This would effectively mean that one could expect to see Red shadows (of varying degrees, of course, depending upon the variables). You asked me to show you a link to show you that the incoming light on Earth has a Yellow-tinge, as I asserted earlier. I did a quick search and found this http://www.atmos.umd.edu/~ezra/whyblue/whypaper.html which you might want to look at. I quote from it: "Since a lot of the blue light is no longer in the original direction, the remaining light becomes more yellow." An extension of my statement that the direct sunlight reaching the Earth's surface is tinged with Yellow, and something which I did NOT want to get into earlier since it is diverging from the point of the discussion, is that due to the direct Sunlight on Earth having (some of) the Blue spectrum removed from it one can expect all terrestrial shadows, especially at Noon, to be Bluish (which they ARE, but we do NOT notice this since the direct Sunlight is way too bright and creates too much contrast). The Blue shadows on Earth are, of course, due to the diffuse Blue light scattered in the atmosphere. The fact that the direct Sunlight illuminating everything on the surface of our planet is in fact Yellow light is something that most people are NOT aware of since our eyes are naturally adjusted to this 'natural' light. It is important for us to distinguish between Raleigh Scattering and dust particle scattering, and do NOT think that either of us have been clear on this. One thing that has become clearer to me is that Raleigh Scattering occurs due to the fact that Blue (and violet) light scatters much easier than do the other colours in the spectrum (this re-affirms the point that virtually ALL planets with atmospheres will exhibit Blue light Raleigh Scattering). Dust particle reflection (of which scattering is a secondary effect, though they can be argued as being one and the same in most cases, I believe), will of course, affect the general 'ambient' (diffuse) colour of it's surroundings and align it with the particular colour spectrum reflected by the particles (i.e. 'Yellow dust', especially in the lower atmosphere, will have an effect of causing objects on the surface to appear more 'Yellow', if the particles are in close proximity to the surface and their density is high enough). This is straight-forward physics and it needn't be as complex as some people believe it to be. We should keep the fundamental Light Spectrum physics in mind when we look at these things, and it is indeed very simple: Absorption and Reflection of varying wavelengths of light - that is all that is going on here - Subtraction and Addition - there is NO 'in-between'. The statement quoted by someone in your Response document, "The reddish particles PREFERENTIALLY ABSORB BLUE LIGHT and effectively act as mirrors by scattering the remaining wavelengths: the color of the atmosphere is therefore pinkish, like the particles themselves", is incorrect since the 'remaining wavelengths' would form Yellow, NOT 'Pink' or even Red; unless they absorb the Turquoise (Cyan) colours, which is probably the case. So, the Limonite is absorbing the Cyan wavelengths? Ok, so then Red is being reflected and scattered, which would mean that we could have a limited 'Red colouring' of objects on the surface; however, this will remain very limited and will be DIFFUSE in nature which would mean that the Direct Sunlight coming through will create too much of a contrast of Pure Light in order to distinguish it since the Direct Sunlight is by far much more intense than the reflected (diffuse) light created by the Limonite. If this were NOT the case (where we have Greater Diffusion than Direct Light), we would see badly-defined shadows on the surface. Anyway, I think we now have our answers as to the True Colours of Mars, thanks to Keith Laney. -------------------------------------- So, what say you? I'm back to square 1 !

blike, I have attached my response as a zip file - it contains some images too. I use Open Office Org and inline images do not work in saved .doc files, hence the zip. Hope it makes sense... I will also post his reply, when I get it. mars_colour_issue.zip

I meant big in KB size - I have some pictures and so forth in the document.

blike - I should have spotted that blue calibration chip! Still, I would have liked to have some 'shocking' evidence - I was kind of hoping that there was a prism on the lander! Well, I suppose the CT would just claim that it was being faked too. I am almost done my response, and I will certainly attach it to this forum - if it's too big, I will cut it down some. Regards.

Thanks blike, I was starting to despair of getting help online for this kind of thing. I have been beavering away and have a summary of my argument which I will now reappraise in the light of your info. Could you tell me if a prism would reveal that blue is absent on Mars? Is this a viable analogy to use - I want to give him something solid that he can wriggle out of.

I see there is not much in the way of answers on this forum. A pity, I had hoped for some serious detail from those in the know. Can I add a question? Q: If you sent a beam of light on Mars through a prism, what would the result be? Would there be a gap in the blue spectrum?

Cap'n thanks, Sunset answer (F) is not yet clear to me: Where did the blue go? The Blue sunset effect (E), see <http://www.exo.net/~pauld/Mars/1viewsurface/viewfrommars.html> I am asking about reflection and absorption because the CT thinks that: "The secondary effect of the dust particles would be one of scattering the incoming light, and thus causing objects on the ground to appear turquoise (or 'bluish') by effectively removing the red component from the direct light." So I want to understand what happens to light as it travels through the layers of the atmosphere on Mars from space to soil. Thanks. PS: I have attached the CT's email to me, so people on this board can read it and perhaps comment. I have to go offline soon and will only be back tomorrow night! ctheory.txt

Hi, first post here. Have been trying to convince this conspiracy theorist (CT) that the red colour on Mars is perfectly natural and in the course of this have discovered that I don't know the basics of light and atmosphere colour. I have looked it up on HowStuffWorks but I have some questions. If anyone here can help me to answer that would help me to argue with the CT. (If this is the wrong place to ask such a question, please point me in the right direction.) If you look up at the blue sky you are seeing many things: A. Blue light scatter-reflected billions of times such that when it hits your eye it comes from many many many sources. B. The other wavelengths, some blue still mixed in, that are mixing together as they hit your eye to be seen as white. B2. Could we say from this that unreflected light from the sun is always white? C. However there is far more blue light coming in so you don't notice the white. C2. Perhaps you notice it as a glare or a brightness? If there is a massive dust-storm or huge fires or terrible smog-pollution we can see the effects of absorption of blue-light. D. Does this then remove most of the blue light and scatter the reddish light through the dust, thus painting it red/brown/tan. D2. Or is the reddish colour of such scenes due only to the absorption of blue light? D3. And if so, should we see the reddish light at all since it's not reflecting off anything? E. On Mars, if the dust absorbs the blue light can you explain the blue sunset effect? Oh, one more: On Earth, an explanation I have read for the yellow/red/orange sunsets is that because of the further distance the light has to travel through the atmosphere, by the time the light reaches your eye all the blue light has scattered away and so we only see the reds etc. F. So, where did the blue scatter to? G. Is the y/r/o colour due to scattering of these colours too? H. Is this due to dust in the air or would the molecules that usually make blue sky work the same magic? Thanks for any help.