This is a basic question regarding Lorentz transformations. Lets say we have two observers - S on Earth and S' which we put on a rocket headed for Alpha Centauri (A.C) =). If i choose 2 events like this: rocket leaves Earth rocket arrives on A.C These two events clearly do not happen on a same place from perspective of an observer S. But what about an observer S'? Would he say that they happen on a same place? I want to know this so i can use ##\Delta x' = 0## in Lorentz transformations.