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:
Quote:
Originally Posted by chrispenycate  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?
Quote:
Originally Posted by chrispenycate 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.