Suppose we have a spacetime diagram like this: Red lines indicating light travel from the moving object to the observer. Object is moving at the speed of 0.8c. At this speed we have: Lorentz factor 1/√(1 - v2/c2)=1/0.6=1.66(6) Relativistic Doppler effect √((1 + β) / (1 - β)) = 3 My question is what does the observer see? According to this diagram At time t=3 (let's say year) observer sees object 1 year old. At t=6, 2 years old. 6/2=3 and we get Doppler effect. As far as i know moving at 0.8c speed in no matter what direction relative to the observer results in time ticking at the speed 0.6 (or 1.66(6) slower). Suppose at t=6 (t'=2) object starts to move towards the observer (same speed). At t=6, object should arrive to the observer, and be 3.6 years old. But how's that possible? How could it be that observer sees the object at time t=6 at both places: arrived, and just starting to making a turn? I don't understand.