From: henry@spsystems.net   
      
   In article <1106458586.410851.123220@c13g2000cwb.googlegroups.com>,   
   Cray74@gmail.com  wrote:   
   >How hot would a nearly ideal black body object get in Mercury orbit?   
      
   Mercury's average distance from the Sun is about 0.39 Earth's, so by the   
   inverse-square law, a black body gets about 6.6x as much solar energy.   
   However, energy radiated as heat is proportional to the fourth power of   
   temperature, so temperature only needs to rise to 1.6x to match this.   
   However however, that's *absolute* temperature, so a black body's   
   temperature goes from around 300K at Earth to around 480K at Mercury,   
   i.e. from around room temperature to around 200degC.   
      
   Caution, I oversimplify in several ways.  Inverse square is not exactly   
   right for a source of finite size and this effect is not negligible for   
   Mercury; Mercury's orbit is noticeably elliptical and the semimajor axis   
   is not really the average distance; and most important, Mercury is not an   
   ideal black body in several ways, and that can make a big difference.   
      
   >I've read that Mercury's daytime temperatures can spike to 800F, but my   
   >calculation for average temperatures at Mercury orbit was 440K/328F.   
      
   See above.  Your calculation's certainly in the right ballpark and is   
   probably correct, but it's for an oversimplified model.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
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