The steam you normally see, say when you boil a pot of water, is actually suspended liquid water droplets entrained in the gas. Since superheated steam has no entrained liquid droplets, it is invisible.
Likewise, we can't see most of the gases in the atmosphere, which are essentially superheated as well.
[edit] although, the sky is somewhat blue from a scattering phenomenon that affects the shorter wavelengths more than the longer ones. Attached is graph of atmospheric radiance looking down from orbit. GRND_RFLT is the what the ground reflects, DRCT_RFLT is the directly sun-illuminated reflection from the ground. The difference is the reflection of the scattered light in the atmosphere. TOTAL_RAD is the total radiance of the path, which includes ground reflected light as well as the scattered light in the path.
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Actually, pure water isn't colorless, it's a bit on the blue-green side, as evidenced by is absorption spectrum. This is one reason that laser mine detection systems use blue-green lasers
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
Each Water droplet will reflect light which make you see steam from a steam kettle. In the superheated region we no longer have droplets as we have vapor whose water molecules, I suspect, are smaller than the visible light wavelength in any spectrum, therefore, there is no reflection and no visibility of superheated steam. That's what I think, am I off base on this?
Interesting. If liquid water is colorless, and pure water vapor is colorless, why is condensing steam white? From IRStuff's post, it seems liquid water color should be the net result when you remove blue - green from plain colorless light, which is ...?
