Poutnik wrote:
Dne 03/12/2016 v 17:48 Mike Dworetsky napsal(a):


A planet or moon or asteroid is a reasonable approximation to a BB
if it does not have an atmosphere, and if it does, the overall
emission of energy will balance the absorption of energy if you take
into account all the sources of opacity and reflection (albedo) at
different wavelengths.


Hm, this is refuted by huan eyes look.
Earth in visible region is far from black body behavior.

True. I said "reasonable approximation". Human eyes are unable to detect
IR radiation.


The very most surfaces are far from be anywhere near the black.

Surfaces are close to BB in terms of absorption and radiation. But the
atmosphere is not.


In the thermal IR region near 10 um
Earth is much closer to BB, especially oceans.

I think that is what I said, more or less. But the atmosphere tends to
block and reflect some of that IR radiation.

Contrast Venus, which has a very thick and opaque atmosphere. The IR
radiation comes from the upper atmosphere, but the surface is much hotter.
When Venus is studied at radio wavelengths, it looks hotter because the
waves penetrate the clouds and we observe the hot surface directly.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)