Quoted from pin2d:If intelligent life on some inhabitable planet that is located 100 light years away from earth created a super powerful telescope and were watching us right now at this moment, they would be seeing what was going on May 13, 1920 (since they are 100 light years away).
(at least I think that is right)
And if you leave Earth now to visit the telescope traveling at the speed of light, in 100 years you can watch your ancestors.