Would the sky be red if the atmosphere was thicker?

  1. Lets say Earths atmosphere with the same composition of gases was 500 bar. Would the sky be red instead of blue because light from the Sun would have to travel through more atmosphere?
    Last edited: Dec 19, 2013
  2. jcsd
  3. The sun itself would be very red. I dont't think the sky would have to be red, as the light that you see would still be the part of the sunlight that is scattered. At sunrise/sunset, the sunlight will take a much longer path through the atmosphere, and only the sun itself and the sky close to it is red.
  4. adjacent

    adjacent 1,533
    Gold Member

    If the atmosphere was thicker,wouldn't the sun look red even at noon?
  5. Yes. What I meant was, that sunset/sunrise with a normal earth atmosphere mimics the situation with a much thicker atmosphere.
  6. So at noon the sky would essentially still be blue but the Sun would look red?
  7. sophiecentaur

    sophiecentaur 13,384
    Science Advisor
    Gold Member

    With a thicker atmosphere, not only blues would be scattered away from the direct path from the Sun. I imagine that you would also see green parts of the spectrum being scattered in the sky, away from the Sun. This could give a more Cyan tint to the sky. This is the sort of colour you can see in the western sky near sunset, where the atmospheric path is long and the normal blue of the sky becomes 'tainted' with a greenish hue and makes that very attractive, temporary greeny blue which we all recognise as a precursor to darkness.
    With a really thick atmosphere (we have to mean 'dense' here, too) the outline of the Sun would also become blurred by scattering (as we get when viewing the Sun through thin cloud at sunset).
  8. It seems to me that the sky would simply be a more intense and brighter blue, since even more blue light would be being scattered. Can someone tell me if this thought is incorrect? I would greatly appreciate it. Thanks.
  9. mfb

    Staff: Mentor

    500 bar? The blue parts would get absorbed long before they reach the surface, and I guess the red parts would get scattered so much you would not see the sun as a disk any more, just a general very dim red glow of the sky.
    Note that nitrogen and oxygen are beyond their critical point then, that might change the absorption.
  10. Maybe I should change the question a little - what if the normal depth of the atmosphere was the distance light travels through the atmosphere at sunset, when the sun is red? Would the whole sky be red, or just a deeper blue?
    Also, another question: when you look out over a flat landscape on fairly clear day, and see a layer of clouds (discrete clouds) at maybe all the same height above the earth, stretching away in the distance and seemingly getting closer to the earth as they near the horizon, are you, in a sense, seeing the curvature of the earth?
  11. mfb

    Staff: Mentor

    Of the order of ~200-300km at sea level pressure. You get a similar effect with less than 50 bar surface pressure and the sun directly above you - but then blue light gets a really hard time reaching the surface, so the rest of the sky will probably look dark red.
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