From: henry@spsystems.net   
      
   In article ,   
   Morenga  wrote:   
   >Does the gravity force only work unidirectional (towards the center of the   
   >earth)...   
      
   Earth's gravity is not directed *precisely* toward its center, because   
   of complications like its equatorial bulge.  But that's not quite what   
   you really wanted to ask...   
      
   >or can outside forces (like the moon or the redistribution of ice/water   
   >masses) also   
   >alter the distribution of mass inside the earth ?   
      
   Only very, very slightly.   
      
   There are tides in the solid Earth as well as in its oceans, because on a   
   planetary scale there is no such thing as a rigid material.  But they are   
   quite small, and their effect on Earth's mass distribution is minute.   
      
   Similarly, redistribution of water (and air) changes Earth's mass   
   distribution enough to be detectable, but in absolute terms the effect is   
   extremely small.   
      
   >Are there any known effects of the variations of earth distance from the sun   
   >on the distribution of mass inside the earth?   
      
   Solar tides are a bit stronger when the Earth is closer, but otherwise no.   
      
   >also read that moon vulcanism is caused by these grav tides.   
      
   There is no known vulcanism on the Moon today.  Except for meteorite   
   impacts, the Moon appears to have been a very quiet place, geologically   
   speaking, for the last couple of billion years.   
   --   
   MOST launched 1015 EDT 30 June, separated 1046,         | Henry Spencer   
   first ground-station pass 1651, all nominal!            | henry@spsystems.net   
      
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