  In a large scale view of the universe, galaxies are the basic unit of
structure. A typical bright galaxy may contain 100 billion stars and span tens
of thousands of light years, but the empty expanses between the galaxies are
much larger still. Galaxies are not randomly distributed in space, but instead
reside in groups and clusters, which are themselves arranged in an intricate
lattice of filaments and walls, threaded by tunnels and pocked with bubbles.
Two ambitious new surveys, the Two-Degree Field Galaxy Redshift Survey (2dFGRS)
and the Sloan Digital Sky Survey (SDSS), have mapped the three-dimensional
distribution of galaxies over an unprecedented range of scales. Astronomers are
using these maps to learn about conditions in the early universe, the matter
and energy contents of the cosmos, and the physics of galaxy formation.
