Thanks to the universe's expansion it is generally true that galaxies with different redshifts will have different distances from us.
Thus when we see multiple galaxies or clusters of galaxies in the same area of the sky we can distinguish which ones are related by comparing their distances through their redshift.
Marko has worked in many fields of astronomy and physics including planetary astronomy, high energy astrophysics, quantum information theory, and supernova collapse simulations. Currently he studies the dark nebulae which form stars.
