The brightness (more properly known as the specific brightness) is the intensity of a radiating source
(i.e., the energy flux per solid angle per unit of frequency), also called the radiance or surface brightness. In
MKS, it is measured in units of
where is the angle to the normal, dA is an area element, is an element of solid angle, and is an element of frequency.
Brightness Temperature, Intensity, Specific Intensity
