Main Question or Discussion Point
They say that the light that reaches us from Alpha Centauri left that star 4 years ago but this assumes that both alpha centauri and the earth are not moving relative to each other. In face Alpha Centauri s approaching us at about 10% of the speed of light. By the Lorenz equations for time T' = G * ( T - X*V/C^2) the X*V term become large so the assumption is not true. So how long ago did the light from Alpha Centauri leave.