# How does one calculate the baseline color of a world's sky, clouds, snow, and water?

I'm working on a planet for a book I'm hoping to write. I want it to be scientifically accurate wherever possible. I know that suspended particles can completely change these colors, but it looks like almost anything that would reasonably be airborne that could change the color would be detrimental to human life. Therefore, I want to calculate the appearance of the atmosphere as though it were determined by Rayleigh scattering alone, then worry about adding additional stuff to it.

The planet is very Earth-like, with a breathable atmosphere of 1.33 atm (78% N2, 19.9% O2 [for now]), a radius of .8, and gravity of .751g, orbiting .52AU from a 4650K star. The star's color is fixed, but I'm willing to tweak the parameters of the planet to improve the setting; I want a sky that is markedly different from what we're used to on Earth. The only problem is that I can't tweak anything if I can't make calculations. The calculations won't be perfect without a thousand variables, but it should be possible to get close enough to leave little room for complaint.

I've found this site, which is good. However, it doesn't have anything between 1atm and 3atm. (Plus I'm not entirely sure I'm interpreting things properly.) I've found other things that illustrate the change in color regarding light temperature OR atmospheric thickness, but not both. I think that snow and clouds, both of which are common enough in this world, should be about the same color. But is that color just going to be the blackbody color of the star? How will it be affected by the Rayleigh scattering of the light on its way down from the star?

What would the natural color of the oceans be, before adding contaminants to the water? I'm guessing they would appear darker than Earth's (since there's less blue from the star) and greener (since they're a higher ratio of green to blue from the star), but, again, I'd like to be able to calculate how much.

Related question: if the atmosphere is thick enough to shift the sky away from blue (probably towards yellow since green sky is so rare?), how would that affect the color of things as seen from space vs the surface? On Earth, it doesn't seem like there's a noticeable difference between colors as seen from the surface and from space (as long as you're not looking through the horizon), but that may just be because I'm used to the changes caused by the atmosphere, so the colors from space seem normal.

Most answers I've seen about color are either handwaving or links to resources that don't give the information for calculating things yourself.

• Hi, Ruined. Due to Stack Exchange policy, you're going to have to break this question down into individual questions if you want it answered here. Rayleigh scattering math is described on the Wikipedia page (en.wikipedia.org/wiki/Rayleigh_scattering), and there's a good discussion of it on the physics page (physics.stackexchange.com/questions/267805/…). Commented Dec 19, 2023 at 17:29
• Might I suggest starting off with the star. That on which everything else depends.... If you tell us the atmospheric composition (gasses, water vapour) and pressure, that should give you a good starting point for general colour balance. You can then ask subsequent questions regarding tweaks to the setup and what to do with the ocean, atmospheric dust, apparent colour of any satellites/other planets as seen from the surface, etc.. Commented Dec 19, 2023 at 23:08
• (a) If you roll your mouse over the tags, you'll discover that science-fiction and science-based are mutually exclusive. Please pick one and delete the other. (b) This handy chart has been a starting point for many a worldbuilder. (c) It's important to realize that all substances absorb different spectra of light. Those absorption spectra are very well known and easily found via internet searches. What you're asking yourself is what will be absorbed vs. what's available to be absorbed. (*Continued*)
– JBH
Commented Dec 20, 2023 at 0:00
• (d) Finally, it's really important that you realize there isn't a single, mathematically or scientifically based method for "calculating" or determining what any one thing will look like on another world. There are too many variables. Consider water: What minerals are in the water? What's the ambient temperature? are there organics? what's in the atmosphere? How much radiation is deflected by the magnetosphere? What's the nature of the star and solar system? Etc. That's why you don't yet have an answer. It's really complicated... which is why even professional authors handwave it.
– JBH
Commented Dec 20, 2023 at 0:03
• OP, you may also find this website interesting. It was originally published in book form, and the text is chock full of references for further reading. Chapter 5 (the chapter I linked) is, I think, the one most relevant to your questions. As Robert mentioned your overall question is too broad to really be answerable here (especially given the complexity of the topic), but maybe this resource can help you narrow in on particular questions that can be their own posts? Commented Jan 25 at 20:58