FUNCTION mpplanck,x,a

	    h  = 6.626e-27        ; erg s
	    c  = 2.998e+10        ; cm s-1
	    kb = 1.381e-16        ; erg K-1
	    bunits =		   'erg s-1 cm-2 sr-1 cm-1'
  
power=h*c/(kb*a[1]*x)
ans=a[0]*double((2* h* c^2 / x^5) / (exp(power) - 1))
return,ans
end