How Can a Red-Hot Object be “Black?
The term “black body” is used because none of the light is reflected from some other source and the intrinsic color of the material is not important. A bar of gold and a bar of black graphite at 3000 degrees C would emit the same color light. The Sun is very close to a theoretical black body in its light emission – all stars are. The Moon is not. The Moon absorbs sunlight and re-emits it in different forms, for example, a lot of visible light is absorbed by the surface and re-emitted in infrared. Incandescent lights, as befits their names, are pretty close to black-body emitters, fluorescent, neon, and sodium-vapor lights are not. As temperature increases, two things happen: • The object emits more radiation at all wavelengths. • The peak of maximum emission shifts toward higher-energy (blue) wavelengths. The very hottest stars emit most of their radiation in the ultraviolet. As an object heats up, the peak of emission creeps into the visible range and the familiar “red hot” color appe
