Sky colour

[Jo Zebedee]

Turquoise is good.

Following the advice that I needed more description of my planets - you know who you are - I have a nice orange sky, but it's the cloud and it's an industrial planet - can I get away with that one? Pleaasse. the rewrite's bad enough.....

 

[alchemist]

Turquoise is good.

Following the advice that I needed more description of my planets - you know who you are - I have a nice orange sky, but it's the cloud and it's an industrial planet - can I get away with that one? Pleaasse. the rewrite's bad enough.....

Industrial planet?

Toxic clouds?

It's almost like Blade Runner.

 

[Ursa major]

* Wonders if that's the updated name for the Blaydon Races.... *

 

[Vertigo]

To be fair I think you can get away with pretty much anything that's not too extreme, certainly Spring's example would be plausible. You asked for examples of authors that have handled this; I have just finished Neal Asher's The Skinner in which the planet Spatterjay has a greenish sky. I thought he had given a reason to do with the star but cannot find it. Basically he just refers to it and never actually describes it. Here are some sample phrases:

The glare of the Earthlight seemed harsh and crystal in contrast to the natural greenish light of Spatterjay’s sun

The sun had become a green dome nested in turquoise clouds

and the sun had become almost distinct in the verdigris sky

The sun set in a silent viridian explosion

One thing to note is that these colours are all reflective and only compromise a small proportion of the light falling on the planet. Most of the light will be direct so even if your sky is blue or orange it does not give a blue or orange cast to everything around you.

 

[Warren_Paul]

Turquoise is good.

Following the advice that I needed more description of my planets - you know who you are - I have a nice orange sky, but it's the cloud and it's an industrial planet - can I get away with that one? Pleaasse. the rewrite's bad enough.....

You can get away with it because of pollution.


Vertigo's suggestion of dust might be my best best. My planet is arid desert-like, so I could kick a lot of dust up into the sky, making it like Mars, which is what I'm after.


EDIT: Sounds like Spatterjay's sun is a red dwarf? I've read somewhere claims that Rayleigh scatterings from a red dwarf could possibly be green, but others argue against this.

 

[Ursa major]

Sounds like Spatterjay's sun is a red dwarf? I've read somewhere claims that Rayleigh scatterings from a red dwarf could possibly be green, but others argue against this.

Perhaps you should ask the author. He has his own sub-forum on the Chrons.

 

[Warren_Paul]

Perhaps you should ask the author. He has his own sub-forum on the Chrons.

Oh right...

 

[David Evil Overlord]

Just throwing out an idea here. I'm sure there will be a scientist along any minute to tell me why it won't work...

Light is refracted when it enters water.

A high-gravity world would have an atmosphere thicker than earth normal. Could such an atmosphere be thick enough to refract light the way water does?

Would this require a world with gravity strong enough to crush puny humans to death, or could we live there?

Would such thick air be breathable, or would puny human lungs collapse or "drown" in such an atmosphere?

And would any of this make the sky a more story-friendly colour?

 

[Vertigo]

Unfortunately DEO I don't think that would work. Water only refracts the light at the boundary with another material. With the atmosphere there is no such boundary except at the outer edges. There might be some bending of the light due to this (in facdt I'm pretty sure there is) but I don't think a thicker atmosphere would do this much more than a thinner one and also refraction only bends light; it would not cause a colour change.

On your other questions. The human body can take an awful lot of pressure so long as the air being breathed in is at the same pressure as the air around the body. This is how scuba diving works and at around 100 feet down (approx 30m) a diver is comfortably existing at around 4 times the pressure of air at the surface. So long as the diver ensures all internal cavities (eg ears) have been equalised as they descend/ascend then all is fine. The main dangers associated with pressure for divers are changing that pressure too quickly ie. the bends if rising to the surface too fast (caused by ntirogen dissolved in the blood I think).

So we are OK operating under 4 times atmospheric pressure. I don't know how much thicker an atmosphere we would have to have to increase pressure more than that but I think it would be enough that it would be the gravity we would suffer from before the air pressure.

It does raise an interesting point. If we were visiting a planet with a significantly higher air pressure than Earth and we weren't wearing pressure suits then we would have to be careful to return to our own pressure (in our ship) slowly to avoid getting the bends as our air supply would have to be delivered at the same pressure to allow us to breathe.

 

[HareBrain]

The main dangers associated with pressure for divers are changing that pressure too quickly ie. the bends if rising to the surface too fast (caused by ntirogen dissolved in the blood I think).

So we are OK operating under 4 times atmospheric pressure.

Even at four atmospheres, the effect of pressure on nitrogen dissolved in the blood can cause nitrogen narcosis (susceptibility varies from person to person), which can be very dangerous if they're required to operate machinery, etc. And much below this, I believe normal compressed air becomes dangerous and more exotic gas mixtures are required, which bring some dangers of toxicity (especially oxygen I think, though I'm no expert). So it's not just the effects of pressure on air cavities you need to be aware of.

 

[Vertigo]

No I agree, I picked that depth and pressure as I believe most people can operate at that with no serious ill effects. What I don't know is how much gravity you would have to have to give that sort of atmospheric pressure. I suspect it would take a lot of gravity and a lot of atmosphere.

 

[chrispenycate]

Not, I suspect, much more gravity. Take Venus as an example; surface gravity 10% less than Earth's, atmospheric pressure 92 times higher, with high temperatures (several hundred degrees) which should increase the number of molecules reaching escape velocity and – er – escaping.

Certainly you need a high percentage of heavy gasses; the amount of carbon dioxide in Venus' atmosphere would make it unhealthy for unmodified humans (as would the temperature and the lack of free oxygen; Venus is possibly not the optimal spot to set up homesteading), but assuming the partial pressure of oxygen was roughly right, you could bulk it out with chemically inactive gasses. CFCs such as freon (dichlorodifluromethane, and no, I didn't have to look it up) would be good, or noble gasses such as neon (not chlorine, methinks)

Blue light is scattered by atmosphere most as it is about the shortest wavelength we can conveniently see. If you have less atmosphere (for example on top of a mountain, where there is still enough air to breath, as long as you are of Tibetan or Andean ancestry and don't exert yourself too much) the sky goes a glorious velvety violet and you can see some stars through it in daylight.

For longer wavelengths, reds and oranges, molecular scattering doesn't work as well. so particular scattering (either solid particles of standardised size, or drops of liquid, generally on a human habitable world water) is recommended.

A cool enough star that doesn't produce much short wavelength radiation (say Marion Zimmer Bradley's "Darkover" Cottman's star) would probably give you a greenish sky (and not much of a suntan, and vitamin D deficiency).

If you think of the low angle light of evening, where the energy has to traverse a lot more thickness of atmosphere than usual, it is not really the sky that goes red. The sun itself does, as short waves are scattered, and the clouds reflect or diffuse this back, but the sky overhead goes an ever darker blue, verging on high altitude violed, before trying "transparent, let darkness through".

 

[Ursa major]

A (slightly) denser and deeper atmosphere can have some noticeable effects. (I'm someone who burns easily even in the sun of southern England, but I had no such problems at the Dead Sea, because the UV component of the light is attenuated there.) However, I didn't notice that the sky had a different colour. Not that I was looking for a difference at the time.


Nothing to do with sky colour, but you might have to tone down the effects on skin colour of living on a world with high air density and/or deeper atmospheres. (Would these worlds be places where tanning parlours were actually fashionable? )

 

[Vertigo]

Chrispy: I sort of suspected that the amount and composition (heavy molecules etc.) of atmosphere had more effect on atmospheric pressure than the gravity but wasn't sure. So thanks for that! And you are absolutely right about high altitude, I have spent a fair bit of time at altitudes above 5000m and apart from anything else it played merry hell with colours on photographic film - snow tended to go a blue-violet colour. Can't say I ever noticed seeing stars in daylight but I can well believe it; might have needed to go higher than my max which is only about 6000m.

Ursa: that's a good point actually; if you have a significantly thicker atmosphere than ours then the amount of UV getting through would be much diminished. They'd probably all be pale and pasty like me (I too burn really badly and even with so called 100% sunblock on when altitude climbing have been known to burn).

 

[juelz4sure]

Another option may be have your planet extremely close to another planet so as to be looking up at another world throughout the day. Your planet may have to be fairly small though I don't know though.

 

[Warren_Paul]

This has started to become a very interesting thread topic. Thanks for the input everyone, given me a lot to think about. David also put a thought in my head:

There is a creationist theory that the earth used to be surrounded by a canopy of water until it was torn down to create a worldwide flood. It is often used to explain the drop in lifespans because now radiation gets through, where before it was blocked by the water vapor.

But there is also scientific arguments refuting it, so not sure whether it is actually possibly or not. If so then the planet could still have its canopy which means light my be seen differently. Which brings me to this:

For longer wavelengths, reds and oranges, molecular scattering doesn't work as well. so particular scattering (either solid particles of standardised size, or drops of liquid, generally on a human habitable world water) is recommended.

Are you talking about having water in the atmosphere here Chrispy, or just meaning surface water? Or have I completely misunderstood?

A cool enough star that doesn't produce much short wavelength radiation (say Marion Zimmer Bradley's "Darkover" Cottman's star) would probably give you a greenish sky (and not much of a suntan, and vitamin D deficiency).

Oh right, this is what I was talking about earlier, so maybe it is true. So much debate going on about this around the internet, I think possibly because most people just don't really know for sure.

 

[David Evil Overlord]

So, Warren, your desert planet might just have a canopy of water around it. How did it get there?

Have you ever read Medusa's Children by Bob Shaw? A piece of alien technology (IIRC) generated a wormhole that stabilised Earth's coastlines by sending excess water out into space during periods of global warming, and retrieved it during periods of global cooling.

The thrown-into-space water formed a tiny water world. Complete with life. Some of it human.

 

[Warren_Paul]

Could explain why its a desert world, most of the water was drawn up into the atmosphere. The how is the question...

I'll have a look into that book, haven't read it.

 

[Bowler1]

As soon as I saw this thread I had to say the sky would have to be blue to work as it is light refracting (all well covered above).

However you could play with the shades of blue in the sky which would I think, still be correct and not lose the better informed readers. Sunsets also could be changed bringing in oranges, reds etc. to suit moods in the story.

Plant colour would also be affected by the different light. It is green on Earth as it makes the best of the light from our sun, (help from biology bods please) it could be a much darker green or possibly red, I think I have heard the Earth was covered in red bacteria for a while.

So still a blue sky, but there could be small changes which would make it clear to the reader this is not Earth we're not.

 

[David Evil Overlord]

I haven't read it for many years, but I'm pretty sure of the facts I've laid out above.

You have that possibility (alien technology), or a variant on Dune (sandworms, big sandworms, and how the hell did they put all the water up there? Sandworms can't fly!), or something natural (a cometary halo orbiting the planet? I don't think that would be very stable. I see impacts. Many impacts. Unless...something stabilised the comet's orbits...we're looping back to alien technology here, perhaps).