Building an Alien World - seeking accurate advice.

[Shalamar]

I'm writing a book, which I plan to self publish.

I'm trying to be as accurate as possible, but have limited time/resources for research.

From a purely practical standpoint it would help drive the point home that we aren't on planet Earth if the sky seemed different. I'll describe their sun but that might not be obvious. I don't have a night scene for the first few chapters, where I can describe the moons and stars.

I've tried to research.... Why is the sky blue. Which gets some philosophical answers. I understand diffusion of short and long wavelengths of light. Along with some atmospheric components and finally humans visual limitations.... All of which contribute to the color of our sky.

Basically I'm hoping someone can validate some of my assumptions.

In a mostly nitrogen/oxygen atmosphere, on a world orbiting one of the cooler red dwarf stars (M8 or M9) in a hospitable zone and with a somewhat human like race without humans limited vision issues. Would it be possible that my aliens would see both the red and blue light mixed into a purple?

Thanks for your help!

 

[Abernovo]

Welcome to the Chrons, Shalamar.
You can have the sky any colour you please. You're worrying too much. If your aliens perceive the red and blue as a purple, then that's what they do. Their eyes possibly work differently to ours but, unless it's absolutely pertinent to the story, do you really need to mention it?

We see a blue sky because that's how we perceive the light reflected and refracted back towards us, as you say. But remember, Person X's perception of colour may be slightly different to Person Y's, and could be very different to Person Z's perception. Your narrative defines the vision -- right until a reader picks up the page and puts their own, erm, perception on the story.

 

[Venusian Broon]

I posted this a wee while back , it might help....

Sky colour

But just to answer your last question, and assuming a scientific stance rather than wibbly-wobbly psychology, because of the imbalance in the way matter deals with wavelength it's really difficult for when light is scattered for red light to be that effective counterbalancing the advantage blue light has.

Note BTW that because it's a 'red' dwarf does not mean that it shines like a doleful red orb. The peak wavelength is near the red end of the spectrum, but it will still be pretty much 'white' as it generates light all over the visible spectrum.

However there could be a number of variables (it is fiction after all ) you might throw up that could force the issue to make a magenta sky - I mention a few different ways you can mess with the 'base case' in the old post! Probably having a planet with little water and lot of coloured dust would help, or perhaps a very polluted planet???

 

[Mirannan]

re This page might be useful:

Sky Colour (not the same as Venusian's )

A couple more points, though. Airborne dust might make a difference to the colour of the sky, especially in a thin atmosphere; the best real-world example is probably Mars, but even Earth's atmosphere becomes locally coloured if some event (lots of Saharan dust or smoke from a big fire) happens. Another example is Titan, which has an orange sky because sunlight is filtered through a thick layer of orange-to-red coloured organics. I imagine that the sky of a chlorine-atmosphere world would likely be green.

I'm not sure about the red star example, but I think it's worth noting that the eyes of native species on a world with more red/infrared and less blue in its sunlight than Earth has would be considerably different from ours. (They might not detect blue at all but be able to see quite well in what is infrared to us.)

Just one more thing: Humans in an SF setting might have considerably different eyesight to ours in the 21st century, with maybe extra cone variants for example and being able to see in UV. In fact, IIRC a significant proportion of modern-day humans have tetrachromatic vision. The majority of them are women, which might explain why women are traditionally held to be better with colours than men are.

On the subject of UV vision, a nice little factoid is that people who have had cataract surgery can see into the UV; the eye's lens has a UV filter, but the retina is sensitive to UV. This apparently became useful in WWII, when elderly people who had had such surgery could see UV signals from boats off the coast of the UK.

 

[Biskit]

From a purely practical standpoint it would help drive the point home that we aren't on planet Earth if the sky seemed different.

Bearing in mind the comments above, telling the reader about the sky might actually prove to be a difficult way of make it clear that the narrative is set on a different planet. Perhaps consider references to plant and animal life - sudden flock of low-flying boojums coming overhead, or a patch of siren nettles singing to lure you in for a sting. That gets you away from tricky explanations of Rayleigh scattering and absorption spectra of organic components in the atmosphere.

 

[Mirannan]

Bearing in mind the comments above, telling the reader about the sky might actually prove to be a difficult way of make it clear that the narrative is set on a different planet. Perhaps consider references to plant and animal life - sudden flock of low-flying boojums coming overhead, or a patch of siren nettles singing to lure you in for a sting. That gets you away from tricky explanations of Rayleigh scattering and absorption spectra of organic components in the atmosphere.

I'm inclined to agree. Other ways might include references to more than one moon, or to more than one sun in the sky; as an example, a planet in the Goldilocks zone of Alpha Centauri A might well be habitable and its orbit would be stable - but star B would be much in evidence.

Or the world might actually be a moon of a gas giant. On the primary-facing side, it would be impossible to miss that, day or night.

 

[Venusian Broon]

That gets you away from tricky explanations of Rayleigh scattering and absorption spectra of organic components in the atmosphere.

My thinking is 'why does he need to explain such physics in his fiction?' I get the sense that the OP'er is the sort of worldbuilder that wants to build something robust and concrete, but then just mentions some clue about it in passing (or if at all!). Sort of getting the groundwork done for the sake of his worldbuilding?

I like doing that, inventing all sorts...then usually just never saying a thing, or if you are lucky a word. I like knowing there's a mass of 'lore' there at my fingertips.

 

[AlexH]

David Farland has some good advice on worldbuilding. A quick Google and I can't find the specific article I was thinking of, but there's some food for thought here: The Wonders of Worldbuilding with David Farland - ali cross

If you don't have time to do a lot of research, perhaps read the relevant sections of the likes of Bill Bryson's A Short History of Nearly Everything (if you haven't already). There are also good worldbuilding resources online e.g. taking escapism to the next level • r/worldbuilding and Worldbuilding Stack Exchange

 

[zmunkz]

In a mostly nitrogen/oxygen atmosphere, on a world orbiting one of the cooler red dwarf stars (M8 or M9) in a hospitable zone and with a somewhat human like race without humans limited vision issues. Would it be possible that my aliens would see both the red and blue light mixed into a purple?

Sure, that could work. Nitrogen/oxygen mixed in the ratios we have here just happens to be blue, as explained best of all by XKCD. Backlight it differently, or mix in traces of other stuff, you can get any color you like. I agree with others that this needn’t be overthought.

What do you mean by humans’ limited vision issues?

**edit:
Found this reference which claims all you need is a hotter sun to get a purple sky. It also notes that human sensitivity to blue is a factor in our sky perception, which means aliens with a more uniform visual acuity may see our sky as purple with nothing altered!

https://www.quora.com/Why-isnt-the-sky-violet-since-violet-light-has-an-even-shorter-wavelength