Under Alien Skies

I've been doing some research recently, trying to get an idea of what a sky on an exoplanet suitable for humans would look like.  It's a frustrating search.  At present, all we can say about alien atmospheres is whether they contain certain elements.

A planet with an atmosphere like Earth's would contain at least water vapour, oxygen, ozone, carbon dioxide, and methane.  We could look for biosignatures on other worlds. Earth's are oxygen, produced by plants and photosynthetic bacteria, and ozone.  

But all that first principles stuff doesn't get me to what I want to know.  I want to stand on the surface of another world and see the sky.  Is is blue like Earth's?  If so, does it have a more greenish tinge?  What's the thickness of the atmosphere, and how would that affect me trying to breathe it?  What's the temperature range of the climate, and can I survive in it?

There are more complicated questions too.  What's the atmospheric circulation like? Does the planet spin on its axis the same way as Earth?  If ithe day length is shorter or longer than Earth's, how does this affect the weather? And what length are the seasons?

I want to stand on an alien world and watch the sunset.  What are the clouds like on that world?  Are they the familiar types we see on Earth, or are there new varieties?  How much dust is there in the atmosphere, and how does that affect the colours of the sunset?

It's estimated that there might be 30 billion planets in our galaxy that could be suitable for life.  But as yet, we're looking at them from afar through telescopes.  And until we find a way of travelling FTL and can send robot probes to some of these exoplanets our knowledge will remain distant.

So I have to make things up when I plonk characters on a new world.  But I can't be certain if my greenish sky actually exists out there, or whether humans would be able to breathe properly on a world where it does.  So I have to go with my dreams, and create the kind of alien skies I want to see.