; NAME:
;      PLANCKFUNC
;
; PURPOSE: 
;      This function calculates the Planck function
;
; CALLING SEQUENCE:
;      Result = PLANCKFUNC(wavel, temp)
;
; INPUTS:
;      Wavel = The wavelength at which to evaluate (can be array) (m)
;      Temp =  The temperature of the object (can be array) (K)
;
; OUTPUT:
;      The intensity of the object in J * s-1 * m-3
;      
; PROCEDURE:
;      Evaluate the Planck function at wavl and temp
;
; RESTRICTION:
;      Arrays must be of the same size
;
; MODIFICATION HISTORY:
;      created April 19 2003 by John Dermody


function PLANCKFUNC, wavel, temp

; evaluate
h = 6.626 * 10.^(-34) ; Js
c = 2.998 * 10.^8     ; m/s
k = 1.381 * 10.^(-23) ; J/K 

pbrightness = ((double(2.) * h * c ^ 2) / (wavel^5) $
              / (exp(h * c / (wavel * k * temp)) - 1)) > 0

return, pbrightness
end