From: gdpusch@NO.xnet.SPAM.com   
      
   beto_z_o@hotmail.com (Beto) writes:   
      
   > According to my calculations, the difference between the longest   
   > distance from earth to the sun and the shorstest one are about 4.8   
   > millions of kilometers.   
   >   
   > Why the temperature doesn't drastically change because of this?   
      
   Because the distance only varies by a few percent.   
      
      
   > If this is because of radiation doesn't being too important this far   
   > from the sun,   
      
   Uh --- just what _do_ you think heats the Earth, then ???  ,:-I   
      
      
   > Where can I find a equation which relates radiation with distance?   
      
   Look up "Inverse Square Law." If you halve the distance, you quadruple the   
   radiant flux. For small changes in distance, the percent change in radiant   
   flux is twice the percent change in distance. However, this is offset by   
   the fact that re-radiation to space goes as the _fourth_ power of temperature,   
   so the percent change in temperature is only 1/4 the percent change in the   
   incoming radiant flux.   
      
   The reason why you don't notice the effect of the Earth's varying distance   
   from the Sun is that the temperature changes due to axial tilt (AKA "seasons")   
   are so much larger than the changes due to distance from the Sun. Also, there   
   are these things called "oceans" that act as huge heat sinks, moderating   
   changes in temperature.   
      
   Nevertheless, the annual change in distance of the Earth from Sun   
   is a small factor that must indeed be included in climate simulations.   
      
      
   -- Gordon D. Pusch   
      
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