How to find the source of the light?
The positions of many galaxies are recorded, so astronomers can point their telescopes to the exact point in the sky that they wish to observe. In addition,the relatively nearby galaxies can be recognised by their appearance,&amp; these are the galaxies most intensively studied. Professional astronomers have memorised most of the stars you will see in the night sky, and the constellations (Sagittarius, Ursa Major, Orion etc) guide them to their target. Those galaxies near the limit of observation are of lttle interest except when something unusual &amp; very luminous happens within them,such as a supernova or gamma ray burst.