Blackbody Is not Actually Black

When we read blackbody, we usually think of a body which is completely black. But, it is not necessary that a body needs to be black to be a blackbody. Actually, in physics we have learned that the body which absorbs all incident rays of all wavelengths from all direction is called blackbody. Or, a body which radiates all kinds of rays of all wavelengths to all directions is called blackbody. However, the most important thing is the energy difference between a blackbody and a body which is staying around that blackbody. For example, we can consider sun as a blackbody with respect to earth.

outer surface of sun by NASA

The whole phenomena is called blackbody radiation. Fundamental quantity that specifies the magnitude of the radiation energy emitted by a blackbody at a certain wavelength at any fixed temperature is called spectral blackbody radiation intensity.


I know, saying things about a blackbody under condensation is funny, but i just can't finish my equations. I will upload my next post on condensation heat transfer again.