Because light moves at finite speed, looking farther into the universe means looking back in time. (imagine.gsfc.nasa.gov)
Cosmology is similar: Because light travels at a finite speed, looking at distant light sources is literally looking back in time. (discovermagazine.com)
Light moves at a finite speed (299,792 kilometers per second, to be precise), so the journey from star to star is a very long one even... (discovermagazine.com)