Apparent Color of the Sun and Sky
The game Rodina features four planets, all with different colored skies. For some reason, the sun is a different color from each planet's surface (use this guide for reference).
The four planets, in order:
- Perun - Purple sky, sun appears green.
- Veles - Red sky, sun appears rust-colored.
- Jarilo - Salmon sky, sun appears blue.
- Morena - Turquoise sky, sun appears red.
Ignoring the fact that this choice is likely just stylistic, how realistic are these scenarios? Is there a correlation between the apparent color of the sky and the color of the Sun? Our planet has a blue sky and the Sun appears yellow, although I've heard of scenarios proposed where the sky could be white and the sun would look blood red (and these conditions have occurred and been documented).
TL;DR: Are the listed combinations of sky color and apparent sun color possible?
This post was sourced from https://worldbuilding.stackexchange.com/q/29956. It is licensed under CC BY-SA 3.0.
1 answer
Rayleigh scattering is the primary reason that the sky is blue. Particles in the atmosphere "scatter" light in random directions. Blue light (along with violet light) has a shorter wavelength, and is therefore scattered more. For this reason, the sky appears blue, because there is scattered blue light appearing from all directions.
However, the sky can appear to be other colors. We often see magnificent shades of yellow, orange, or red near sunset and sundown. This is because the Sun is lower in the sky, and the light travels further. It is therefore scattered more (across all wavelengths) and the longer wavelengths dominate.
How can we apply this to the present case? Well, simply change the densities of the atmospheres. A greater density should shift the sky color to the redder end of the spectrum; a lower density should shift the sky color to the bluer end of the spectrum. Play around a bit and see what you can do.
The Sun appears yellow because shorter wavelengths - such as orange and yellow - deviate less from their original path. Thus, the redder light that is emitted from the Sun stays closer to its original path than the bluer colors do. Again, play around with the density to see if you can change this. A greater density might simply mean that redder wavelengths dominate even more, in which case you'll see a redder Sun in all cases of higher density atmospheres (retaining the same composition as Earth's).
This lecture has an excellent summary diagram of this at the end, if you're interested:
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