Suppose we measure a flux in photons from this star to be

             F = 10^5 photons / sec / cm^2.


   Q:  Calculate the luminosity of the star assuming a distance
               of d' = 100 pc = 3.08 x 10^(20) cm


            L'  =    F *  4 pi (d')^2      

                                 
            L'  =    10^5 photon/s/cm^2 * 4 * pi * ( 3.08 x 10^(20) cm )^2


            L'  =    1.19 x 10^(47)  photon/sec



   Q:  Calculate the luminosity of the star assuming a distance
               of d  = 105 pc = 3.23 x 10^(20) cm

     true   L   =    10^5 photon/s/cm^2 * 4 * pi * ( 3.23 x 10^(20) cm )^2


     true   L   =    1.31 x 10^(47)  photon/sec




   Q:  What is the fractional error in the luminosity of the star?


                                  ( L' - true L )
           fractional error  =   -----------------
                                         L'


                             =    0.010    

                             =    approx 10 percent


   Q:  How does that compare to the fractional error in the distance?

            
           The fractional error in luminosity is TWICE the
           fractional error in distance.