Summary of Distance Scales

To summarize, the discussion in this chapter about structure in the Universe: we find that typical spacings between stars in galaxies are of order 1 pc, large galaxies have diameters of 100 kpc, and are separated in groups and clusters by distances of order 1 Mpc. Clusters have dimensions of order 1-10 Mpc, and are separated by similar distance scales, superclusters and voids occur on scales of 100 Mpc, and the largest structures yet observed extend over distances > 150 Mpc.

The following image illustrates the important large distance scales in the Universe.