It isn’t until you get to considerably larger scales that the universe can be
considered as isotropic. Consider a sphere 200 Mpc in diameter, centered on
your navel. Figure 2.2d shows a slice through such a sphere, with superclus-
ters of galaxies indicated as dark patches. The Perseus-Pisces supercluster is
on the right, the Hydra-Centaurus supercluster is on the left, and the edge of
the Coma supercluster is just visible at the top of Figure 2.2d. Superclusters
are typically ∼ 100 Mpc along their longest dimensions, and are separated
by voids (low density regions) which are typically ∼ 100 Mpc across. These
are the largest structures in the universe, it seems; surveys of the universe
on still larger scales don’t find “superduperclusters”.