A Red Ship flies past the Earth as people celebrate Jan 1, 2501, on
the planet's surface.

      Earth frame:   x2  =  0 yr
     
                     t2  =  1 yr


      Ship frame:    x2' =  gamma * (x2 - v*t2)

                         =  2.294 * (0  - 0.9*1)  =  -2.06 yr

                     t2' =  gamma * (t2 -  (v*x2)/c^2 ) 

                         =  2.294 * (1  -  (0.9*0)/1^2 )  =  2.294

  Q:  By what factor is Joe's clock
      running slow, according to the planet-based
      observers?


         Joe's clocks are running slower than Earth's clocks,
         at a rate of  (1 / 2.294)  =  0.436   time Earth's clocks.


 
  Q:  What is the distance between planets,
      according to Joe and the crew
      of the ship?


         Joe sees planets moving past his ship at a speed of 0.9c.
         It takes 0.484 years of ship's time for planet P1 to 
         appear after they leave Earth.  So the distance from
         Earth to P1 must be

                 distance  =  (speed) * (time)  =  (0.9c) * (0.484 yr)

                           =  0.436 yr

         Note that this is the same as the answer one could derive
         using length contraction on the distance between the planets
         in the Earth frame.