From: tjroberts137@sbcglobal.net   
      
   On 9/20/17 9/20/17   5:53 AM, Luigi Fortunati wrote:   
   > The spaceship C is firm with respect to the star S distant 4 years-light.   
      
   By "firm" I assume you mean "at rest".   
      
   > Be AB any diameter of the star.   
   > From A and B start two light rays arriving at the spaceship, forming the ABC   
   > triangle whose height then measures 4 light-years.   
   > Next to the spacecraft C passes spaceship D approaching gamma=4 to star S.   
   > For the contraction of the lengths, star S (for spaceship D) is only 1   
   > year-light distant and therefore the height of the ABD triangle measures   
   > only 1 year-light (instead of 4).   
   > Geometrically, the angle in D is 4 times larger than the angle in C.   
   > How is this all possible if the rays of light in the common point C e D are   
   > the same?   
      
   The rays of light from the star are all the same. But measurements of the angle   
   between them is frame dependent. This is no different from other measurements   
   being frame dependent, such as velocities, momenta, time intervals, distances   
   along relative motion, etc.   
      
   Tom Roberts   
      
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