Sci-fi story help, how would you be able to look back in time?

Theoritically you could see anything that has ever happened on earth from space if you had a big enough telescope mounted to an engine that could move faster than light. You would need to know how far away to go from the earth before looking back, but if the telescope was strong enough you could focus it on the precise spot and see what happened. Stick an ultra-powerful computer to that and it would, theoritically, work.