Not a physicist or a mathematician, but reading about cosmology whenever I have a chance. Alfa Centauri is 4.37 light-years away, so I conclude that it takes 4.37 x 2 traveling at 1/2 the speed of light. However, I am assuming that 4.37 x 2 is measured here on Earth. How much time has elapsed for the pilot of the spaceship? In other words: How do we measure the distance to Alfa Centauri? Because of time dilation I am assuming it takes less time for the pilot to get there. I have heard of length reduction while moving, but i don't see how this applies to the distance to Alfa Centauri. So the question is: What is the real distance to Alfa Centauri? I am confused.