The idea of the Earth moving away while you're time travelling is one that always let's otherwise thought-stimulating time-travel (*snort*) movies down. HOWEVER, if you COULD time-travel, then you could "jump" through time and measure the change in distance between things like the Earth, the Sun, the stars without having to worry about your own motion (because you cease to exist while time-travelling)! At last! An external frame of reference!
Wooo!