Q:  Suppose a cloud has a temperature 
      T = 20 Kelvin.  At what wavelength
      does its radiation reach a peak?



         If the cloud emits as a blackbody,
         then the peak wavelength will be

                       2,900,000 nm-K
            lambda  =  --------------
                           T (K)


                       2,900,000 nm-K
                    =  -------------
                          20 K


                    =  145,000 nm


                    =  145,000 x 10^(-9) m

                    =  145 x 10^(-6) m

                    =  0.145 x 10^(-3) m

                    =  0.145 mm