All objects emit electromagnetic radiation continuously. The radiation
emitted by a solid object (or a liquid) has certain fundamental characteristics
which are described using the term ``blackbody radiation''. This term has
nothing to do with an object's color, but instead it refers to how it absorbs
and emits radiation. A blackbody is considered to be perfect absorber and
emitter of energy (everything it absorbs it will emit back, with no energy
lost). For this course we will assume the earth's surface and liquid water in
the atmosphere emit blackbody radiation with the following
characteristics:
they emit radiation over a wide range of wavelengths; the amount of
energy emitted at each wavelength is not the same however. If you plot the
amount of energy emitted at each wavelength, you get a curve like that shown
in Figure 2.7. Note that the wavelength where most of the sun's energy comes
from (or "wavelength of peak emission") is in the visible portion.
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