On still large scales, the universe is still anisotropic. Consider, for ex-
ample, a sphere 3 Mpc in diameter, centered on your navel (Figure 2.2c).
This sphere contains the Local Group of galaxies, a small cluster of some 40
galaxies. By far the most massive and most luminous galaxies in the Local
Group are our own Galaxy and M31, which together contribute about 86% of
the total luminosity within the 3 Mpc sphere. Thus, within this sphere, our
Galaxy and M31 define a preferred direction.