Thermal or “Blackbody” Radiation
Any opaque body produces
E-M radiation characteristic of its temperature. It follows the “Planck curve” shape, which has a peak. The
wavelength of the peak follows “Wein’s law”: lmax(nm)=3x106 / T(K)
(so hotter sources are bluer).
The total energy emitted (or total area under the curve)
by hotter sources of the same size
goes up like T4 , and they are brighter at all
wavelengths.
This is called “blackbody” radiation
because it’s what you get from a little hole in a dark cavity, or a black-looking absorber (which is also an excellent emitter). A better name is “thermal” radiation, because it is related to T.