

Penguins' coats are colder than surrounding air - Patient0
http://www.bbc.co.uk/nature/21669963

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lutusp
Unfortunately, there's no explanation given, and that would have been
relatively easy. Because thermal radiation is often much more efficient than
convection, surfaces frequently fall below the ambient air temperature by
radiating their heat energy directly into space.

The phenomenon called "radiation fog" is a side effect of this -- the fog
forms over a surface that becomes colder than the air above it by direct
radiation into space, which causes condensation of water vapor in the adjacent
air mass. If the surface was the same temperature as the air, this couldn't
happen.

Radiation fog:

<http://www.crh.noaa.gov/jkl/?n=fog_types>

