From: sylvia@not.at.this.address   
      
   On 21/07/2017 3:43 PM, LuigiFortunati wrote:   
   > If we place a telescope to the solar system from the space for 10 years,   
   > we see 10 Earth revolutions around the Sun and just over 3650   
   > rotations on it.   
   >   
   > If at the end of 10 years the revolutions were 80 and the rotations   
   > were over 29200, then it all went 8 times faster.   
   >   
   > Well, that's exactly what happens to the twin who travels for 10   
   > years and he finds the aged 80-year-old terrestrial brother.   
   >   
   > The traveling twin telescope has actually observed a total of 80   
   > revolutions and more than 29200 land rotations.   
   >   
   > Around his spaceship everything has moved much faster than our usual!   
   >   
   > Can we say that from the porthole of the relativistic spacecraft the   
   > universe appears frantically speeded?   
   >   
      
   No. You have to consider the effects of changing distances to objects   
   which affects the time it takes light to arrive from them. This is   
   analogous to the Doppler effect.   
      
   During the outbound trip the Earth looks as if it's rotating more   
   slowly than usual, both because the Earth rotates more slowly in   
   the travelling twin's frame due to time dilation, and because each   
   subsequent rotation is seen from further away, meaning the light   
   took longer to make the trip.   
      
   When the travelling twin reverses his direction, the Earth looks   
   as if it's rotating faster than usual. It's still rotating more   
   slowly in the the travelling twin's frame due to time dilation, but   
   now the light has less distance to travel for each successive turn,   
   and this effect more than cancels out the time dilation.   
      
   By the time the travelling twin gets back to Earth, he's seen more   
   rotations than the number of 24 hour periods[*] he's experienced.   
      
   Sylvia   
      
   [*] Strictly, about 24 hours minus four minutes, because he's   
   observing sidereal days, not solar days.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)