Cosmic black-body radiation

IR radiation is sometimes incorrectly called radiant heat, because warm bodies emit IR radiation and bodies that absorb IR radiation are warmed. However, IR radiation is not itself heat. This EM radiation is called black body radiation. Such waves are emitted by all material objects. For example, the background cosmic radiation (2.7 K) emits microwaves room temperature objects (295 K) emit IR rays the sun (6000 K) emits yellow Hght the solar corona 10 K emits X rays. 

The development of new low-temperature detection technology and the launch of the Cosmic Background Explorer (COBE) satellite by NASA in 1989 helped to resolve this problem. The results from these observations were amazing - an almost perfect black body curve (Figure 2.3) with a black body temperature of 2.725 0.002 K and a maximum wavelength of the radiation at kmax = 1.05 mm. 

Figure 2.3 An almost-perfect black body spectrum for the cosmic background radiation. Figure courtesy of NASA/COBE Science Team...

Black bodies emit radiation at all wavelengths. Using the spreadsheet, calculate the contribution to the visible spectrum from the cosmic microwave background in the visible region of the spectrum. 

Cosmic microwave background radiation Fossil radiation surviving form the Big Bang with a black body temperature of 2.725 K. 

The temperature then drops to a value limited by the 3 °K black body background radiation and is controlled by the temperature of the grains and the ionization by high energy cosmic rays on the one hand, and saturation of the cooling transitions on the other. 

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