Relativity, Twin Paradox, Time Dilation, Lenghts Contraction, Lorentz Transformation.
in motion with a rigid rod of length equal to the Earth- planet distance attached to its tail). In that case, of course, the spaceship with the tail of length d is the alter ego of a moving spaceship (tailless). In the frame of the Earth S, the tail end of the spaceship reaches the Earth at the