function planck,t,gnu

;------------------------------------------------------------------
;
; Purpose:
;
;   Computes the blackbody radiance according to Planck's function
;
; Parameters:
;
;   input:
;      t   = temperature in K
;      gnu = wavenumber (1/cm),  10000/microns = 1/cm
;
;   output:
;      result = radiance in Watts/(cm^2 sr cm^-1) 
;
; source: Mark Hervig 
;
;------------------------------------------------------------------

  c1     = 1.1926E-05 * 1.e-7
  c2     = 1.4398
  result = c1 * gnu^3 / ( exp(c2*gnu /T) -1.0 )

  return,result
  end