Alien Skies

[Crazy Tom]

I was just wondering, doe the sky have to be blue or shades thereof, or are there other possibilities?

[Coronach]

I was just wondering, doe the sky have to be blue or shades thereof, or are there other possibilities?

To my knowledge, the sky of any given planet could be any color in the visible spectrum. I think it would depend on the makeup of the atmosphere.

[Crazy Tom]

To my knowledge, the sky of any given planet could be any color in the visible spectrum. I think it would depend on the makeup of the atmosphere.

The sky on any terra-compatible planet.

[Coronach]

The sky on any terra-compatible planet.

As in...could the sky on a human-sustainable planet be anything but blue? I am not sure about this. I mean, maybe, but then again I don't know enough about atmospheric science to postulate whether or not a change in atmosphere to cause a color change would be breathable.

[Puddle-Jumper]

I don't think so.... but I haven't studied physics in over a year so I can't remember it much

[_Famrir_]

i think the reason they sky is blue is because of the high concentrations of nitrogen in the atmosphere which scatters the light thus making it blue although 21% of the atmosphere is oxygen too.

[Coronach]

Might be a little complex, but it addressed this:

http://en.wikipedia.org/wiki/Diffuse_sky_radiation

http://en.wikipedia.org/wiki/Rayleigh_Scattering

[Splitsecond]

Humans can only naturally survive on Earth. Every single other world would have different properties like atmosphere, gravity, tidal effects (if any), sunlight etc. All of these can have severe impacts on the development and health of a human if it was born in that environment. We have only evolved to deal with the current situation on some parts of this planet. Earth is likely to be the only human habitable world. Look at tests done in zero gravity on animals and plants or tests done on people in oxygen rich/depleted, hot/cold sunny/dark environments and you'll begin to realise how fragile the window of habitability is.

[Opener]

Yeah, but then you have the Enkarans. Their physiology was adapted for a specific set of circumsatnces, so I can extend that to other humans. Besides, what we see of the human genome is only around 1% of its total capacity, so I imagine that we could survive quite handily on another world with different enough conditions that would produce viable vegetation, yet a different-colored sky. It may take a few generations, but we could do it.

[Splitsecond]

That 1% thing makes no sense. Evolution would take a long time to re-adapt us for life on a planet with half Earth gravity. You would also need to have some mutations in the first generation that would allow people to at least survive long enough to have children and bring those children to adulthood. The muscles needed to allow for a woman to give birth will be significantly weaker if the woman lived her life on a half Earth gravity planet. She may not even be able to give birth.

[Coronach]

Humans can only naturally survive on Earth.

Massively bold claim.

Earth is likely to be the only human habitable world.

Even more of a bold claim

Look at tests done in zero gravity on animals and plants or tests done on people in oxygen rich/depleted, hot/cold sunny/dark environments and you'll begin to realise how fragile the window of habitability is.

The muscles needed to allow for a woman to give birth will be significantly weaker if the woman lived her life on a half Earth gravity planet

Why you assume we'd seek out planets with drastically altered gravity is odd to me.

Also...this is all way off-topic. As mentioned in my above post, I am not knowledgeable enough to say whether or not humans could survive on a planet that had (for instance) a red sky. The only reason I say this, though, is because I'm not sure exactly what it would take atmospherically to achieve a uniformly red sky.

I am, however, positive that blue is not the only color a sky can be

[Splitsecond]

Most of the planetary bodies that humans have sent probes to do not have blue skies. In fact I think Earth is the only thing in our solar system to have blue skies. We don't know how common blue skies are in the universe. Almost every other planetary body in the universe will not be like Earth. Almost all will be at least slightly different, so could have wildly different skies.

Humans can only naturally survive on Earth.

Massively bold claim.

Earth is likely to be the only human habitable world.

Even more of a bold claim

Look at tests done in zero gravity on animals and plants or tests done on people in oxygen rich/depleted, hot/cold sunny/dark environments and you'll begin to realise how fragile the window of habitability is.

The muscles needed to allow for a woman to give birth will be significantly weaker if the woman lived her life on a half Earth gravity planet

Why you assume we'd seek out planets with drastically altered gravity is odd to me.

They are not bold claims. The human body optimally works within a relatively small window of temperatures, a highly specific atmospheric composition, a small range of g-forces, a small range of background radiation spectra, a specific composition of sunlight and a myriad of other factors. Tests have shown the tolerances for humans and the chances of finding another planet with exactly the right conditions to naturally sustain us without serious health problems is ridiculously small. For most of the history of this world we couldn't successfully live here without technological intervention. We can't live on a lot of the Earth today without technological intervention. The number of worlds where you could simply take a human family, dump them there with nothing and expect them to survive (a naturally habitable world) is 1 in a very large number. As a result you can easily assume that Earth is the only one nearby and all nearby human habitable worlds (Earth) have blue skies.

[Coronach]

They are not bold claims. The human body optimally works within a relatively small window of temperatures, a highly specific atmospheric composition, a small range of g-forces, a small range of background radiation spectra, a specific composition of sunlight and a myriad of other factors. Tests have shown the tolerances for humans and the chances of finding another planet with exactly the right conditions to naturally sustain us without serious health problems is ridiculously small.

Really, tests have shown this? I'm not being facetious, I am just surprised they could test all these factors to such a definitive extent.

And maybe I misinterpreted your original claims. If not, they are still quite bold claims, especially considering the estimates for just how many planets may be out there.

For most of the history of this world we couldn't successfully live here without technological intervention. We can't live on a lot of the Earth today without technological intervention.

Okay...so we'll use technological intervention on other planets to make them more habitable. That is, after all, the key aspect of our species' survival.

I mean, if you're trying to say that the likelihood of finding another Earth is pretty small, then I might be more inclined to agree with you.

The number of worlds where you could simply take a human family, dump them there with nothing and expect them to survive (a naturally habitable world) is 1 in a very large number.

You didn't say naturally habitable, and you certainly didn't even imply this hypothetical originally. As you said, people would have trouble surviving on their own even in some places on Earth.

As a result you can easily assume that Earth is the only one nearby and all nearby human habitable worlds (Earth) have blue skies.

When did nearby come into the picture? You made very general, very all-encompassing claims. If that's not what you initially meant, then fine.

[Crazy Tom]

You guys realize we're talking about SG here? Didn't the Ancients terraform a whole load of planets?

I'm asking whether those planets can have different colored skies, maybe because their star is s different class (but the planet is still within it's habitable belt). I imagine this would be the only real variable is these planets were terraformed.

[Splitsecond]

The original question was 'do all terra-like planets have blue skies'. If the term Terra-like is taken to mean rocky then the answer is no. If the term is taken to mean potentially human populated then it must be pointed out that all worlds shown in Stargate are effectively exactly like Earth. The existence of worlds exactly like Earth is possible but so highly improbable as to make a proper answer impossible. We would probably never have a sample of Earth-like planets big enough to give a statistically significant answer. As a result you might as well draw a conclusion based on the ones nearby, which is Earth. If a planet with a blue sky is give the answer value 1 and a planet with no blue sky is given the answer value 0, the answer based on the evidence is 1 (error range: - 1).