From: jsfmiller@netzero.net   
      
   AlexT wrote:   
   > Folks   
   >   
   > Reading through various articles about the upcoming launch of the New   
   > Horizon probe I did not manage to locate any solid information about   
   > the amount of energy & light available from the Sun on Pluto.   
   >   
   > I remember having read something like "about the size and brightness   
   > of Venus as seen from earth".   
   >   
   > If it's true I find it really remarkable that an earth based   
   > telescope would manage to "see" Pluto...   
   >   
   >   
   > --alexT   
   >   
      
   The brightness of an object at a given distance requires knowledge of   
   the luminosity of the light-emitting object and that distance via:   
      
   b = L/(4pi)d^2   
      
   The luminosity of the Sun is 3.9 x 10^26 Watts and the average distance   
   to Pluto is 5.916 x 10^12 meters.  This will tell you the watts/square   
   meter at Pluto.  To compare it to what we get here, put in the Earth's   
   average distance of 1.5 x 10^11 meters or do ratios of the equation for   
   Pluto compared to here, eliminating the L/(4pi) term.   
      
   The ratio of brightness number can be used to determine the magnitude of   
   the Sun compared to its magnitude here:   
      
   m(E)-m(P) = 2.5 log [(b(P)/b(E)]   
      
   m(E) = -26.8, so you can do the ratio of brightness of Pluto to Earth to   
   calculate the magnitude of the Sun at Pluto.  Venus at its most   
   brilliant comes in about -4.4, so you can check your answer against that   
   marker to answer your question.   
      
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