Just an easy question.. What does each observer see? The earth one obviously sees time running slower on the spaceship. When the spaceship observer heads out, I assume he sees time running slower on the earth frame? As he heads back, what does he see? I'm finding it hard to reconcile the fact that the spaceship observer sees time running slower on the earth with the fact that he should be able to see the (say) 2 years pass on earth during his 1 day in space. Time dilation depends on the direction of relative velocity?