Red Giant visual spectrum

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Topic author
psCargile
Posts: 25
Joined: 01.01.2007
With us: 13 years 7 months

Red Giant visual spectrum

Post #1by psCargile » 03.08.2012, 08:14

I suppose this pertains to both the physics side and the Celestia side; I'm writing a series of stories and I want to be as realistic as possible for depicting the sky as seen on a planet that has an atmosphere comparable to Earth around a red giant. I had read from an online pdf (that I cannot find now) that red giants do not emit in the blue and UV spectrum, would I be correct in concluding that no blue light as pertaining to what the eye sees would be bathing the planet? Or do the red giants emit across the entire visible light spectrum, just more so in red and less in blue?

As I have built my planet in Celestia, I have recently been playing around with the Rayleigh and Mie scattering and have looked at Friger's post on the subject at Celestia Matters, as well as other websites after an internet search, so I understand the scattering as far as it gives the sky it's color, and have played around with values to see what effect they have, so I'm able to get the kind of coloring and effects I want, however, I have no clue as to how realistic my sky color is--a sort of rosy sulfuric yellow is what I've always had in mind. If there is no blue light coming in, am I correct to conclude that an oxygen, nitrogen, and water vapor atmosphere will have no blue light to scatter (and from my nascent understanding Rayleigh scattering isn't entirely applicable), so my Rayleigh value for blue should remain at 0? Or is copying the Earth's scattering parameters from the solarsys.ssc file at better option? I did try that, but I'm thinking that like most of Celestia, scattering is rendered from the Red-Green-Blue values and is independent from the solar light source, and that one can create all sorts of impossibilities.

Code: Select all

      
      Mie 0.0011
      MieAsymmetry -0.27
      Rayleigh [ 0.0041 0.0017 0.00001 ]
      Absorption [ 0 0 0 ]
      MieScaleHeight 12


These are the values that I'm using. I does give me a blue sunrise/sunset, so would there be a plausible atmospheric phenomenon to cause that (I know about Mars' sunsets), or should I play around with the absorbtion values to get rid of it. I've striving more for realism than flight of fancy. I am aware of a 1/lambda^4 ratio from the Celestia Matters thread, but have no idea how it should be implemented.

That's pretty much it: blue? Some blue? Or no blue?

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Hungry4info
Posts: 1133
Joined: 11.09.2005
With us: 14 years 10 months
Location: Indiana, United States

Re: Red Giant visual spectrum

Post #2by Hungry4info » 03.08.2012, 10:40

psCargile wrote:would I be correct in concluding that no blue light as pertaining to what the eye sees would be bathing the planet? Or do the red giants emit across the entire visible light spectrum, just more so in red and less in blue?
The latter,

See this site:
http://www.classzone.com/books/earth_sc ... page05.cfm

ajtribick did some work on this subject a while back and found that the skies for a planet that, under a G-type star would be blue, would be greyer under an M-type star. His work was for M dwarf stars, but I think it should be directly applicable to M giant stars.

See:
viewtopic.php?f=6&t=16196
http://forum.celestialmatters.org/viewtopic.php?t=389

I wish I could do more than direct you to similar work, but I'm not particularly knowledgeable about the topic myself.
Current Setup:
Windows 7 64 bit. Celestia 1.6.0.
AMD Athlon Processor, 1.6 Ghz, 3 Gb RAM
ATI Radeon HD 3200 Graphics

Topic author
psCargile
Posts: 25
Joined: 01.01.2007
With us: 13 years 7 months

Re: Red Giant visual spectrum

Post #3by psCargile » 03.08.2012, 17:13

Thanks. That's all I needed was a confirmation that there would be some blue.


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